151
Case Report
Femoral nerve entrapment in a dog with diffuse idiopathic skeletal hyperostosis A. Lai1; J. Culvenor1; C. Bailey1; S. Davies2 1Department
of Small Animal Surgery, North Shore Veterinary Specialist Centre, Sydney, Australia; 2Veterinary Imaging Associates, Sydney, Australia
Keywords Femoral nerve, diffuse idiopathic skeletal hyperostosis, DISH, entrapment, compression
Summary Objective: To report femoral neuropathy caused by nerve entrapment associated with diffuse idiopathic skeletal hyperostosis (DISH). Study Design: Case report. Animal: Seven-year-old female spayed Boxer dog. Results: Entrapment of the right femoral nerve due to DISH caused a femoral nerve deficit and atrophy of muscle groups associated with the affected nerve. A combination Correspondence to: Alen Lai North Shore Veterinary Specialist Centre Small Animal Surgery Department 64 Atchision St. Crows Nest, NSW 2065 Australia E-mail: [email protected]
of computed tomography and magnetic resonance imaging was performed to provide a diagnosis. Amputation of the right transverse process of the sixth lumbar vertebra at the level of nerve entrapment relieved the neurological abnormality. Conclusions: Nerve entrapment leading to neurapraxia may occur concurrently with DISH and surgery in this case was successful in restoring function. Clinical relevance: Peripheral neuropathy from nerve entrapment should be considered in patients with DISH. Surgical amputation of impinging osseous structures may be indicated for relief of femoral neuropathy.
Vet Comp Orthop Traumatol 2015; 28: 151–154 http://dx.doi.org/10.3415/VCOT-14-09-0139 Received: September 9, 2014 Accepted: December 16, 2014 Epub ahead of print: February 4, 2015
Introduction Diffuse idiopathic skeletal hyperostosis is usually an incidental finding. In most dogs it is either subclinical or associated with only mild clinical signs of spinal pain and dysfunction (1, 2). Diffuse idiopathic skeletal hyperostosis is characterized by excessive ossification of ligaments and entheses, along the ventral and lateral aspects of the vertebral column (2, 3). The aetiologic factors are not yet clear (4). Langeland and colleagues suggested a hereditary basis in Boxers whereas Morgan and Stavenborn hypothesized that canine DISH may be secondary to other disease processes such
as hypoparathyroidism and hypercalcitonism (5, 6). Diffuse idiopathic skeletal hyperostosis differs from spondylosis deformans because spondylosis deformans originates from the endplates of vertebral bodies (7). Canine DISH has been sparsely defined in the current literature. In retrospect, it may have been more appropriate to use the term DISH in some of the earlier reported cases of severe bridging spondylosis deformans in dogs (1). Reports correlating DISH with clinical signs in dogs are limited to two cases with extreme stiffness and axial and appendicular skeletal pain; the severity of abnormalities resulted in euthanasia in both of these cases (6, 8). The
aim of this report is to describe the clinical features, diagnostic methods and management of a case with femoral nerve entrapment associated with DISH.
Case report A seven-year-old, 22 kg, female spayed, Boxer dog was initially presented to a primary accession practice with a two week history of right hindlimb lameness and dragging of the right hindlimb. The cause of the lameness was assessed to be related to hip pain and the dog was subsequently treated with pentosan polysulphatea (3 mg/ kg SC), acetyl glucosaminea (4.8 mg/kg SC), and carprofenb (2.2 mg/kg PO SID). Lameness and limb function were reported to worsen after one week of treatment. Radiographs of the lumbar spine, pelvis and hindlimbs revealed extensive bone formation on the ventral aspect of the vertebral column and resulting fusion of vertebral segments, consistent with a diagnosis of DISH. The dog was subsequently referred for further investigation. Physical examination showed a moderate degree of lameness of the right hindlimb. Proprioception and withdrawal reflexes were considered normal bilaterally. There was marked atrophy of the right quadriceps muscle group with an absent patellar reflex. The contralateral patellar reflex was considered normal. Gentle palpation of the proximal region of the right quadriceps muscle group elicited
a
Synovan: Ceva Aniaml Health Pty Ltd. Glenorie, NSW, Australia b Rimadyl: Pfizer Australia, West Ryde, NSW, Australia
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Figure 1 a) T2-weighted fat suppressed dorsal planar image including the coxofemoral joints and proximal thigh. There is increased T2 signal in the quadriceps musculature of the right hindlimb. b) T1-weighted post-contrast fat suppressed transverse planar image at the level of the ischiatic tuberosities (x). There is increased signal in the quadriceps musculature in the right hindlimb representing increased contrast-enhancement. White arrows outline the margins of right quadriceps musculature with increased T2 signal and increased contrast-enhancement.
a severe pain response; the dog withdrew the limb and vocalized concurrently. A similar reaction was not elicited in the contralateral limb. The neurological localization was a right femoral neuropathy. Magnetic resonance imagingc of the spine and proximal part of the pelvic limbs was performed. Examination revealed mild to moderate intervertebral disc protrusion at the levels of the sixth to seventh lumbar (L) vertebrae and from L7 to first sacral (S) vertebrae and right quadriceps atrophy with slight T1 and T2-hyperintensity and increased contrast-enhancement when compared to surrounding musculature (▶ Figure 1). Signs of extensive bridging bone were present ventral and lateral to the lumbar spine consistent with DISH. The right iliopsoas muscle belly contained a wider linear focus of hyperintensity in pre and post-contrast T1-weighted studies and subtle STIR hyperintensity ventral to the L6 transverse process when compared with the left psoas muscle. In T2-weighted axial images there was a larger area of T2-hyperintensity within the right psoas muscle in the region of formation of the femoral nerve (▶ Figure 2). Unfortunately, interpretation of signal change in the region of the right femoral nerve was complicated by absence of acquisition of any fat saturated post-contrast T1-weighted images.
c
Philips Achieva 1.5T A-series: Philips Healthcare, Best, The Netherlands
Computed tomographyd of the lumbosacral spine was performed before and after intravenous administration of iodinated contrast mediume (2 ml/kg, iodine 240 mg/ ml). Reformatted images were examined using diagnostic image viewing softwaref. Examination showed impingement of the path of the L5 nerve root on the right at the L5-L6 level between a large spondylotic element associated with DISH and the transverse process of L6 vertebra (▶ Figure 3). A d GE LightSpeed Series 4.X: General Electric Company, Silverwater, NSW, Australia e Omnipaque: GE Healthcare Australia, Rydalmere, NSW, Australia f e-film: Merge Healthcare, Chicago, USA
Figure 2 T2-weighted transverse planar image showing a focus of increased T2-hyperintensity (white arrows) within the right psoas muscle (compare with the left psoas muscle) where the femoral nerve is forming.
similar spondylotic body was present on the contralateral side. No enlargement or abnormal contrast enhancement of the right femoral nerve could be identified within the spinal canal on CT. Imaging findings were most consistent with femoral nerve compression (▶ Figure 4). Surgical exploration of the right femoral nerve was performed via a lateral approach. The dorsal attachment of the internal and external oblique muscles were transected and retracted ventrally. The iliocostalis lumborum muscle and the longissimus lumborum muscle were elevated from the dorsal aspect of the transverse process of L5-L7 and retracted dorsally. The iliopsoas muscle was elevated from the ventral aspect of the transverse process of L5-L7 and retracted ventrally. The fifth lumbar nerve supplying the right femoral nerve was identified and was entrapped between the osseous spondylotic elements located on the ventrolateral aspect of L5 and the transverse process of L6. The intertransversarii lumborum muscles were elevated from the transverse process of L6 and the transverse process was amputated proximal to the level of nerve compression using bone rongeurs. The surgical approach to this region of the spine proved to be challenging due to the depth of dissection required to expose the region of interest. A biopsy sample of the right femoral nerve was collected and sent for histopathology. A Jackson-Pratt drainage device was placed prior to closure of the surgical wound. Postoperatively, analgesia was provided by a methadoneg constant rate infusion at 0.1 mg/kg/hr for the first 24 hours and was reduced to 0.05 mg/kg/hr for a further 24 hours. The methadone constant rate infusion was stopped 48 hours after surgery, and was followed by buprenorphineh subcutaneous injections (0.01 mg/kg) every eight hours for a further 24 hours. The nerve biopsy sample was fixed in 10% neutral buffered formalin. The entire piece of tissue was routinely processed, embedded in paraffin, longitudinally sectioned at 4 microns, and stained with haeg Methadone Hydrochloride: Troy Lab Pty Ltd, Glendenning, NSW, Australia h Temgesic: Reckitt Benckiser, West Ryde, NSW, Australia
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A. Lai et al.: Femoral nerve entrapment in a dog with DISH
matoxylin and eosin. Histological examination of the tissue revealed mild axonal swelling of the nerve tissue and patchy infiltration of the nerve sheath by adipose tissue consistent with nerve compression. No evidence of active inflammation or neoplasia was noted in the examination. The dog recovered uneventfully and was subsequently discharged from hospital four days postoperatively. Postoperative medication dispensed at discharge was carprofenb (2.2 mg PO SID) for a period of two weeks. Re-evaluation at two weeks postoperatively showed return of the right patellar reflex and a significant improvement in the lameness. Two months postoperatively, the lameness was completely resolved with return to a normal level of activity. The muscle atrophy noted prior to surgery was found to have mostly resolved. At telephone follow-up six months after surgery, the dog was reported by the owner to have remained free of lameness.
Discussion To our knowledge, this is the first reported case of femoral nerve compression caused by DISH. Neurological examination of this dog localized the anatomical lesion to the right femoral nerve, its constituent nerve roots of L4-L6 or unilateral grey matter from L4-L6. Atrophy of the right quadriceps muscle group was consistent with femoral denervation and suggested that the lesion was located proximal to the division of the femoral nerve into individual nerves supplying each head of the quadriceps. Initial physical findings revealed severe signs of pain on palpation of the proximal region of the quadriceps muscle group (mechanoallodynia). This display of allodynia was consistent with neuropathic pain. Neuropathic pain is defined as pain initiated or caused by a primary lesion or dysfunction in the nervous system and is typically attributable to injury or disease that damages the axon or soma of sensory neurons or disrupts the myelin sheath (9, 10). A key clinical feature of neuropathic pain is the development of abnormal sensation, which is often characterized by allodynia (painful sensation caused by a normally innocuous stimuli – demon-
Figure 3 Dashed black line indicates site of entrapment of the right L5 nerve root between the large spondylotic element and the L6 transverse process. The shaded area shows the extent of the large area of bone production or spondylotic element extending laterally from the body of L6. A similar spondylotic element is present on the left side of the L6 vertebral body.
strated in this case), hyperalgesia (exaggerated response to a normally painful stimuli), paraesthesia (tingling, prickling, burning sensation), and dysaesthesia (spontaneous or unprovoked unpleasant abnormal sensation) (9–11). The pathophysiology of neuropathic pain differs from normal nociception. Neuropathic pain is thought to occur because of a reorganisation of sensory transmission within the nervous system that occurs after nerve injury (10). Injury to the
nerves causes disruption of the glial ensheathment and subsequently allows adjacent denuded axons to make contact, facilitating electrical and chemical cross-excitation. It has also been described that nerve injury may disrupt the inhibition of pain transmission neurons in the dorsal horn (12, 13). This mechanism leading to loss of inhibitory process is also thought to contribute to spontaneous pain, hyperalgesia, or allodynia after nerve injury.
Figure 4 Three-dimensional rendered image made in Osirix showing the L6 transverse process outlined in white. The dark blue line represents the path of the L5 nerve as it descends to form part of the femoral nerve. The L5 nerve passes ventral to the L6 spinous process (light blue segment), and in this patient, it is entrapped between the L6 spinous process and the large spondylotic element extending lateral to the L6 vertebra.
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The overall prevalence of DISH in the general dog population was reported to be 3.8%, compared to the significantly greater prevalence of 40.6% in the Boxer breed (7). Dog breeds represent close gene pools with a high degree of familiar relationship, thus the high prevalence in the Boxer dog may be suggestive of a genetic origin of DISH (7). Magnetic resonance imaging of the hindlimbs in this case revealed right quadriceps atrophy that was homogeneously hyperintense to the surrounding muscle on the T1- and T2-weighted images. This finding is consistent with denervation of the muscles. The right iliopsoas muscle belly contained an area of hyperintensity which followed the anatomical course of the femoral nerve. Differential diagnoses for this region of increased signal included inflammatory infiltrate, oedema or neoplasia. Computed tomography was performed prior to surgery to better categorize the lesion of the femoral nerve and its association with the concurrent DISH detected in this case. The purpose of the CT examination in this case was to provide additional information defining the osseous structure in relation to the femoral nerve anatomy. The CT findings were highly suggestive of femoral nerve entrapment characterized by the impingement on the path of the nerve root on the right at L5-L6 between perispinal osseous formation associated with DISH and the transverse process of L6 vertebra. These findings were consistent with right femoral nerve compression, leading us to surgically explore the region to relieve the femoral nerve compression. However, no clinical signs were noted relating to a femoral neuropathy on the contralateral side. This may be explained by the poor sensitivity of CT to assess the presence of peripheral nerve compression. This illustrates the importance of interpreting CT findings alongside physical examination findings as well as using other imaging modalities such as MRI, as performed in this case. Publications describing the surgical approach to this specific location of the spine are lacking to our knowledge. Three approaches to the femoral nerve have been
described previously, however these pertained to the portion of the femoral nerve that is distal to the region of pathology of our case. A ventral abdominal approach provided good exposure to the iliopsoas muscle and the femoral nerve in experimental dogs, however it did not allow examination of the constituent roots of the femoral nerve (13). In one other case of femoral neuropathy secondary to a traumatic iliopsoas muscle injury, the femoral nerve was approached laterally by dissecting between the gluteus medius muscle dorsally and the iliacus ventrally (14). Other authors described a similar modified approach, but in addition they performed a ventral iliac osteotomy to allow the sartorius and tensor fascia lata muscles to be reflected ventrally. The latter approach permitted the cranial two-thirds of the iliopsoas musculature containing the femoral nerve to be examined (15). These three previously described approaches allowed examination of the femoral nerve distal to its constituent roots (L4-L6). In our case, we reported a novel surgical approach to the L4-L6 nerve roots at the level of the transverse process. The described approach allowed good exposure of the nerve and the transverse processes for amputation. In this report, we describe an unusual case of DISH found to be associated with femoral nerve compression. To our knowledge, there have been no previous reports documenting the successful treatment of the nerve compression by surgical amputation of the affecting vertebral transverse process. In conclusion, compression neuropathy must be considered in a dog with radiographic evidence of DISH, especially if mechanoallodynia and nerve deficits are concurrently detected. Our experience with this case suggests that surgical decompression of the affected nerve is an appropriate therapy for DISH related neuropathy. Acknowledgements
The authors wish to acknowledge Kate Patterson (MediPics and Prose) for providing assistance in the illustrations of the figures included in this report.
Conflict of interest
None of the authors of this paper has a financial or personal relationship with other persons or organisations that could inappropriately influence or bias the content of this paper
References 1. Kranenburg HC, Voorhout G, Grinwis GC, et al. Diffuse idiopathic skeletal hyperostosis (DISH) and spondylosis deformans in purebred dogs: a retrospective radiographic study. Vet J 2011; 190: 84–90. 2. Ortega M, Gonclaves R, Haley A. Spondylosis deformans and diffuse idiopathic skeletal hyperostosis (DISH) resulting in adjacent segment disease. Vet Radio Ultrasound 2012; 53: 128–134. 3. Togni A, Kranenburg HJ, Morgan JP, et al. Radiographic and MRI characteristics of lumbar disseminated idiopathic spinal hyperostosis and spondylosis deformans in dogs. J Small Anim Pract 2014; 55: 343–349. 4. Li H, Jiang LS, Dai LY. Hormones and growth factors in the pathogenesis of spinal ligament ossification. Eur Spine J 2007; 16: 1075–1084. 5. Langeland M, Lingaas F. Spondylosis deformans in the boxer: estimates of heritability. J Small Anim Pract 1995; 36: 166–169. 6. Morgan JP, Stavenborn M. Disseminated idiopathic skeletal hyperostosis (DISH) in a dog. Vet Radiol Ultrasound 1991; 31: 65–70. 7. Krannenburg H, Westerveld L, Verlaan J. The dog as an animal model for DISH? Eur Spine J 2010; 19: 1325–1329. 8. Woolf CJ. Dissecting out mechanisms responsible for peripheral neuropathic pain: implication for diagnosis and therapy. Life Sci 2004; 74: 2605–2610. 9. Bridges D, Thompson SW, Rice AS. Mechanism of neuropathc pain. Br J Anaesth 2001; 87: 12–26. 10. Mathews KA. Neuropathic pain in dogs and cats: If only they could tell us if they hurt. Vet Clin North Am Small Anim Pract 2008; 38: 1365–1414. 11. Cashmore RG, Harcourt-Brown TR, Freeman PM, et al. Clinical diagnosis and treatment of suspected neuropathic pain in three dogs. Aust Vet J 2009, 87: 45–50. 12. Taylor BK. Pathophysiologic mechanisms of neuropathic pain. Curr Pain Headache Rep 2001: 5: 151–161. 13. Wilson JW. Ventroabdominal approach to the lumbosacral plexus of the dog. Am J Vet Res 1978; 39: 691–693. 14. Stepnik MW, Olby N, Thomson RR, et al. Femoral neuropathy in a dog with iliopsoas muscle injury. Vet Surg 2006; 35: 186–190. 15. Harcourt-Brown TR, Granger N, Smith PM, et al. Use of a lateral surgical approach to the femoral nerve in the management of two primary femoral nerve sheath tumours. Vet Comp Orthop Traumatol 2009; 22: 229–232.
Vet Comp Orthop Traumatol 2/2015
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Case Report
Femoral nerve entrapment in a dog with diffuse idiopathic skeletal hyperostosis A. Lai1; J. Culvenor1; C. Bailey1; S. Davies2 1Department
of Small Animal Surgery, North Shore Veterinary Specialist Centre, Sydney, Australia; 2Veterinary Imaging Associates, Sydney, Australia
Keywords Femoral nerve, diffuse idiopathic skeletal hyperostosis, DISH, entrapment, compression
Summary Objective: To report femoral neuropathy caused by nerve entrapment associated with diffuse idiopathic skeletal hyperostosis (DISH). Study Design: Case report. Animal: Seven-year-old female spayed Boxer dog. Results: Entrapment of the right femoral nerve due to DISH caused a femoral nerve deficit and atrophy of muscle groups associated with the affected nerve. A combination Correspondence to: Alen Lai North Shore Veterinary Specialist Centre Small Animal Surgery Department 64 Atchision St. Crows Nest, NSW 2065 Australia E-mail: [email protected]
of computed tomography and magnetic resonance imaging was performed to provide a diagnosis. Amputation of the right transverse process of the sixth lumbar vertebra at the level of nerve entrapment relieved the neurological abnormality. Conclusions: Nerve entrapment leading to neurapraxia may occur concurrently with DISH and surgery in this case was successful in restoring function. Clinical relevance: Peripheral neuropathy from nerve entrapment should be considered in patients with DISH. Surgical amputation of impinging osseous structures may be indicated for relief of femoral neuropathy.
Vet Comp Orthop Traumatol 2015; 28: 151–154 http://dx.doi.org/10.3415/VCOT-14-09-0139 Received: September 9, 2014 Accepted: December 16, 2014 Epub ahead of print: February 4, 2015
Introduction Diffuse idiopathic skeletal hyperostosis is usually an incidental finding. In most dogs it is either subclinical or associated with only mild clinical signs of spinal pain and dysfunction (1, 2). Diffuse idiopathic skeletal hyperostosis is characterized by excessive ossification of ligaments and entheses, along the ventral and lateral aspects of the vertebral column (2, 3). The aetiologic factors are not yet clear (4). Langeland and colleagues suggested a hereditary basis in Boxers whereas Morgan and Stavenborn hypothesized that canine DISH may be secondary to other disease processes such
as hypoparathyroidism and hypercalcitonism (5, 6). Diffuse idiopathic skeletal hyperostosis differs from spondylosis deformans because spondylosis deformans originates from the endplates of vertebral bodies (7). Canine DISH has been sparsely defined in the current literature. In retrospect, it may have been more appropriate to use the term DISH in some of the earlier reported cases of severe bridging spondylosis deformans in dogs (1). Reports correlating DISH with clinical signs in dogs are limited to two cases with extreme stiffness and axial and appendicular skeletal pain; the severity of abnormalities resulted in euthanasia in both of these cases (6, 8). The
aim of this report is to describe the clinical features, diagnostic methods and management of a case with femoral nerve entrapment associated with DISH.
Case report A seven-year-old, 22 kg, female spayed, Boxer dog was initially presented to a primary accession practice with a two week history of right hindlimb lameness and dragging of the right hindlimb. The cause of the lameness was assessed to be related to hip pain and the dog was subsequently treated with pentosan polysulphatea (3 mg/ kg SC), acetyl glucosaminea (4.8 mg/kg SC), and carprofenb (2.2 mg/kg PO SID). Lameness and limb function were reported to worsen after one week of treatment. Radiographs of the lumbar spine, pelvis and hindlimbs revealed extensive bone formation on the ventral aspect of the vertebral column and resulting fusion of vertebral segments, consistent with a diagnosis of DISH. The dog was subsequently referred for further investigation. Physical examination showed a moderate degree of lameness of the right hindlimb. Proprioception and withdrawal reflexes were considered normal bilaterally. There was marked atrophy of the right quadriceps muscle group with an absent patellar reflex. The contralateral patellar reflex was considered normal. Gentle palpation of the proximal region of the right quadriceps muscle group elicited
a
Synovan: Ceva Aniaml Health Pty Ltd. Glenorie, NSW, Australia b Rimadyl: Pfizer Australia, West Ryde, NSW, Australia
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Figure 1 a) T2-weighted fat suppressed dorsal planar image including the coxofemoral joints and proximal thigh. There is increased T2 signal in the quadriceps musculature of the right hindlimb. b) T1-weighted post-contrast fat suppressed transverse planar image at the level of the ischiatic tuberosities (x). There is increased signal in the quadriceps musculature in the right hindlimb representing increased contrast-enhancement. White arrows outline the margins of right quadriceps musculature with increased T2 signal and increased contrast-enhancement.
a severe pain response; the dog withdrew the limb and vocalized concurrently. A similar reaction was not elicited in the contralateral limb. The neurological localization was a right femoral neuropathy. Magnetic resonance imagingc of the spine and proximal part of the pelvic limbs was performed. Examination revealed mild to moderate intervertebral disc protrusion at the levels of the sixth to seventh lumbar (L) vertebrae and from L7 to first sacral (S) vertebrae and right quadriceps atrophy with slight T1 and T2-hyperintensity and increased contrast-enhancement when compared to surrounding musculature (▶ Figure 1). Signs of extensive bridging bone were present ventral and lateral to the lumbar spine consistent with DISH. The right iliopsoas muscle belly contained a wider linear focus of hyperintensity in pre and post-contrast T1-weighted studies and subtle STIR hyperintensity ventral to the L6 transverse process when compared with the left psoas muscle. In T2-weighted axial images there was a larger area of T2-hyperintensity within the right psoas muscle in the region of formation of the femoral nerve (▶ Figure 2). Unfortunately, interpretation of signal change in the region of the right femoral nerve was complicated by absence of acquisition of any fat saturated post-contrast T1-weighted images.
c
Philips Achieva 1.5T A-series: Philips Healthcare, Best, The Netherlands
Computed tomographyd of the lumbosacral spine was performed before and after intravenous administration of iodinated contrast mediume (2 ml/kg, iodine 240 mg/ ml). Reformatted images were examined using diagnostic image viewing softwaref. Examination showed impingement of the path of the L5 nerve root on the right at the L5-L6 level between a large spondylotic element associated with DISH and the transverse process of L6 vertebra (▶ Figure 3). A d GE LightSpeed Series 4.X: General Electric Company, Silverwater, NSW, Australia e Omnipaque: GE Healthcare Australia, Rydalmere, NSW, Australia f e-film: Merge Healthcare, Chicago, USA
Figure 2 T2-weighted transverse planar image showing a focus of increased T2-hyperintensity (white arrows) within the right psoas muscle (compare with the left psoas muscle) where the femoral nerve is forming.
similar spondylotic body was present on the contralateral side. No enlargement or abnormal contrast enhancement of the right femoral nerve could be identified within the spinal canal on CT. Imaging findings were most consistent with femoral nerve compression (▶ Figure 4). Surgical exploration of the right femoral nerve was performed via a lateral approach. The dorsal attachment of the internal and external oblique muscles were transected and retracted ventrally. The iliocostalis lumborum muscle and the longissimus lumborum muscle were elevated from the dorsal aspect of the transverse process of L5-L7 and retracted dorsally. The iliopsoas muscle was elevated from the ventral aspect of the transverse process of L5-L7 and retracted ventrally. The fifth lumbar nerve supplying the right femoral nerve was identified and was entrapped between the osseous spondylotic elements located on the ventrolateral aspect of L5 and the transverse process of L6. The intertransversarii lumborum muscles were elevated from the transverse process of L6 and the transverse process was amputated proximal to the level of nerve compression using bone rongeurs. The surgical approach to this region of the spine proved to be challenging due to the depth of dissection required to expose the region of interest. A biopsy sample of the right femoral nerve was collected and sent for histopathology. A Jackson-Pratt drainage device was placed prior to closure of the surgical wound. Postoperatively, analgesia was provided by a methadoneg constant rate infusion at 0.1 mg/kg/hr for the first 24 hours and was reduced to 0.05 mg/kg/hr for a further 24 hours. The methadone constant rate infusion was stopped 48 hours after surgery, and was followed by buprenorphineh subcutaneous injections (0.01 mg/kg) every eight hours for a further 24 hours. The nerve biopsy sample was fixed in 10% neutral buffered formalin. The entire piece of tissue was routinely processed, embedded in paraffin, longitudinally sectioned at 4 microns, and stained with haeg Methadone Hydrochloride: Troy Lab Pty Ltd, Glendenning, NSW, Australia h Temgesic: Reckitt Benckiser, West Ryde, NSW, Australia
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A. Lai et al.: Femoral nerve entrapment in a dog with DISH
matoxylin and eosin. Histological examination of the tissue revealed mild axonal swelling of the nerve tissue and patchy infiltration of the nerve sheath by adipose tissue consistent with nerve compression. No evidence of active inflammation or neoplasia was noted in the examination. The dog recovered uneventfully and was subsequently discharged from hospital four days postoperatively. Postoperative medication dispensed at discharge was carprofenb (2.2 mg PO SID) for a period of two weeks. Re-evaluation at two weeks postoperatively showed return of the right patellar reflex and a significant improvement in the lameness. Two months postoperatively, the lameness was completely resolved with return to a normal level of activity. The muscle atrophy noted prior to surgery was found to have mostly resolved. At telephone follow-up six months after surgery, the dog was reported by the owner to have remained free of lameness.
Discussion To our knowledge, this is the first reported case of femoral nerve compression caused by DISH. Neurological examination of this dog localized the anatomical lesion to the right femoral nerve, its constituent nerve roots of L4-L6 or unilateral grey matter from L4-L6. Atrophy of the right quadriceps muscle group was consistent with femoral denervation and suggested that the lesion was located proximal to the division of the femoral nerve into individual nerves supplying each head of the quadriceps. Initial physical findings revealed severe signs of pain on palpation of the proximal region of the quadriceps muscle group (mechanoallodynia). This display of allodynia was consistent with neuropathic pain. Neuropathic pain is defined as pain initiated or caused by a primary lesion or dysfunction in the nervous system and is typically attributable to injury or disease that damages the axon or soma of sensory neurons or disrupts the myelin sheath (9, 10). A key clinical feature of neuropathic pain is the development of abnormal sensation, which is often characterized by allodynia (painful sensation caused by a normally innocuous stimuli – demon-
Figure 3 Dashed black line indicates site of entrapment of the right L5 nerve root between the large spondylotic element and the L6 transverse process. The shaded area shows the extent of the large area of bone production or spondylotic element extending laterally from the body of L6. A similar spondylotic element is present on the left side of the L6 vertebral body.
strated in this case), hyperalgesia (exaggerated response to a normally painful stimuli), paraesthesia (tingling, prickling, burning sensation), and dysaesthesia (spontaneous or unprovoked unpleasant abnormal sensation) (9–11). The pathophysiology of neuropathic pain differs from normal nociception. Neuropathic pain is thought to occur because of a reorganisation of sensory transmission within the nervous system that occurs after nerve injury (10). Injury to the
nerves causes disruption of the glial ensheathment and subsequently allows adjacent denuded axons to make contact, facilitating electrical and chemical cross-excitation. It has also been described that nerve injury may disrupt the inhibition of pain transmission neurons in the dorsal horn (12, 13). This mechanism leading to loss of inhibitory process is also thought to contribute to spontaneous pain, hyperalgesia, or allodynia after nerve injury.
Figure 4 Three-dimensional rendered image made in Osirix showing the L6 transverse process outlined in white. The dark blue line represents the path of the L5 nerve as it descends to form part of the femoral nerve. The L5 nerve passes ventral to the L6 spinous process (light blue segment), and in this patient, it is entrapped between the L6 spinous process and the large spondylotic element extending lateral to the L6 vertebra.
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A. Lai et al.: Femoral nerve entrapment in a dog with DISH
The overall prevalence of DISH in the general dog population was reported to be 3.8%, compared to the significantly greater prevalence of 40.6% in the Boxer breed (7). Dog breeds represent close gene pools with a high degree of familiar relationship, thus the high prevalence in the Boxer dog may be suggestive of a genetic origin of DISH (7). Magnetic resonance imaging of the hindlimbs in this case revealed right quadriceps atrophy that was homogeneously hyperintense to the surrounding muscle on the T1- and T2-weighted images. This finding is consistent with denervation of the muscles. The right iliopsoas muscle belly contained an area of hyperintensity which followed the anatomical course of the femoral nerve. Differential diagnoses for this region of increased signal included inflammatory infiltrate, oedema or neoplasia. Computed tomography was performed prior to surgery to better categorize the lesion of the femoral nerve and its association with the concurrent DISH detected in this case. The purpose of the CT examination in this case was to provide additional information defining the osseous structure in relation to the femoral nerve anatomy. The CT findings were highly suggestive of femoral nerve entrapment characterized by the impingement on the path of the nerve root on the right at L5-L6 between perispinal osseous formation associated with DISH and the transverse process of L6 vertebra. These findings were consistent with right femoral nerve compression, leading us to surgically explore the region to relieve the femoral nerve compression. However, no clinical signs were noted relating to a femoral neuropathy on the contralateral side. This may be explained by the poor sensitivity of CT to assess the presence of peripheral nerve compression. This illustrates the importance of interpreting CT findings alongside physical examination findings as well as using other imaging modalities such as MRI, as performed in this case. Publications describing the surgical approach to this specific location of the spine are lacking to our knowledge. Three approaches to the femoral nerve have been
described previously, however these pertained to the portion of the femoral nerve that is distal to the region of pathology of our case. A ventral abdominal approach provided good exposure to the iliopsoas muscle and the femoral nerve in experimental dogs, however it did not allow examination of the constituent roots of the femoral nerve (13). In one other case of femoral neuropathy secondary to a traumatic iliopsoas muscle injury, the femoral nerve was approached laterally by dissecting between the gluteus medius muscle dorsally and the iliacus ventrally (14). Other authors described a similar modified approach, but in addition they performed a ventral iliac osteotomy to allow the sartorius and tensor fascia lata muscles to be reflected ventrally. The latter approach permitted the cranial two-thirds of the iliopsoas musculature containing the femoral nerve to be examined (15). These three previously described approaches allowed examination of the femoral nerve distal to its constituent roots (L4-L6). In our case, we reported a novel surgical approach to the L4-L6 nerve roots at the level of the transverse process. The described approach allowed good exposure of the nerve and the transverse processes for amputation. In this report, we describe an unusual case of DISH found to be associated with femoral nerve compression. To our knowledge, there have been no previous reports documenting the successful treatment of the nerve compression by surgical amputation of the affecting vertebral transverse process. In conclusion, compression neuropathy must be considered in a dog with radiographic evidence of DISH, especially if mechanoallodynia and nerve deficits are concurrently detected. Our experience with this case suggests that surgical decompression of the affected nerve is an appropriate therapy for DISH related neuropathy. Acknowledgements
The authors wish to acknowledge Kate Patterson (MediPics and Prose) for providing assistance in the illustrations of the figures included in this report.
Conflict of interest
None of the authors of this paper has a financial or personal relationship with other persons or organisations that could inappropriately influence or bias the content of this paper
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