Polymyositis usually presents with progressive proximal muscle weakness, increased serum levels of muscle enzymes, inflammatory changes on muscle biopsy, and characteristic electromyographic (EMG) abnormalities. Motor unit action potential (MUAP) changes of configuration, duration, and amplitude are the most frequently observed EMG abnormality. Fibrillation potentials are commonly seen and tend to reflect active disease, diminishing after successful medical management or disease regression. Other muscle diseases can present with similar electromyographic abnormalities, thereby necessitating muscle biopsy for definitive diagnosis. Key words: polymyositis electrodiagnosis EMG fibrillation potentials MUSCLE & NERVE 14~310-315 1991

AAEM CASE REPORT #22:

POLYMYOSITIS LAWRENCE R. ROBINSON, MD

Polymyositis is a disease with an incidence approximating 5 per million."3 Patients usually present with progressive proximal limb and neck weakness, sometimes associated with muscle pain. Associated laboratory findings include elevated serum muscle enzymes, inflammatory changes on muscle biopsy, and characteristic abnormalities on needle electromyography. The electrodiagnostic examination is an integral component of the complete evaluation of such patients.

consistent with Raynaud's phenomenon. She denied dysphagia or dyspnea. On physical examination, she was markedly weak proximally in a symmetrical distribution: neck flexors 215, shoulder abductors 2+15, elbow flexors 4-15, wrist extensors 3+/5, hip flexors 4-/5, knee extensors 515, and ankle dorsiflexors 515. Muscles were tender to palpation in the proximal arm. Sensation and muscle stretch reflexes were normal. Her fingers were puffy, suggestive of early scleroderma skin changes.

CASEREPORT

A 33-year-old woman presented with a one-month history of fatigue, proximal upper extremity myalgias, difficulty raising her arms above the horizontal, and a weight loss of 12 pounds. These complaints developed after a 4-day history of flu-like symptoms consisting of rhinorrhea and diarrhea. Physical examination at the time of her initial presentation was remarkable for proximal upper extremity muscle weakness, in the 3/5 range. Two months after onset of symptoms, she was referred to a tertiary care facility for further evaluation. Additional questioning revealed a history

From the Department of Rehabilitation Medicine, University of Washington School of Medicine, Seattle, Washington. Address reprints requests to AAEM, 21 Second Street S W , Suite 306, Rochester, MN 55902 Accepted for publication April 26, 1990.

CCC 0148-639X1911040310-06 $04 00 0 1991 Lawrence R. Robinson, MD Published by John Wiley & Sons, Inc

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AAEM Case Report #22:Polyrnyositis

Laboratory Studies. Initial laboratory evaluation by her local physician included: erythrocyte sedimentation rate (ESR) 35 mm/h, creatine kinase (CK) 1320 IU/L (nl 25 to 225), SGPT 72 IU/L (nl < 45), SGOT 99 IU/L (nl < 41), and LDH 392 IU/L (nl < 210). The CBC, platelet count, thyroid function tests, alkaline phosphatase, bilirubin, and RPR were all normal. Upon referral to the tertiary care center, CK was still elevated at 510 IU/L (nl < SO), other laboratory values included: SGOT 79 IUIL (nl < 34), SGPT 47 IU/L (nl < 37), alkaline phosphatase 71 IU/L (nl < loo), and aldolase 20.6 IU/g Hb (nl 1.2 - 7.6). Because of mild intermittent substernal pressure, an upper GI with barium swallow was performed; this revealed mildly decreased peristalsis of the esophagus.

Electrodiagnostic Examination. The electrodiagnostic examination was performed about 2 months after onset of symptoms.

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Table 1. Results of nerve conduction studies in the right lower extremity. Nerve

Stim.

Rec.

Lat. (rns)

Ampl. (pV)

Dist.

C.V.

Peroneal (m)

Ankle Knee Leg

EDB EDB Ankle

4.6 10.4 3.6 (Pk)

5200 5200 14

8.0 29.5 14.0

51

Sural (s)

METHODS

Motor conduction studies of the peroneal nerve and sensory studies of the sural nerve were performed using standard techniques.*' The peroneal F wave was recorded as the shortest onset latency of 10 responses. A monopolar electrode was used for the needle examination. Commonly described methods were used for grading of spontaneous activity and description of recruitment abnormalities.*' In addition to the routine needle examination, for more careful analysis, motor unit action potentials (MUAPs) were isolated by means of a trigger and delay line. MUAP parameters were compared to those reported in a normal population using monopolar electrodes lo; normal values are different for concentric Only right-sided muscles were examined to allow for muscle biopsy on the left.

F Latency 41.2

Needle examination was performed on the right deltoid, biceps, triceps, first dorsal interosseous, gluteus medius, adductor longus, vastus medialis, tibialis anterior, and medial gastrocnemius (Table 2). Increased insertional activity was noted in most upper and lower extremity muscles. Sustained fibrillation potentials (both spike form and positive sharp wave form) were most marked in proximal upper extremity muscles (biceps and triceps) though they were present in most muscles tested. N o complex repetitive discharges or myotonic discharges were observed. Motor unit action potentials (MUAPs) were of low amplitude and short duration in proximal upper extremity muscles. Duration was slightly reduced in other muscles as well, though amplitudes were normal. Polyphasia was not seen. Recruitment of MUAP firing was felt to be early in proximal upper extremity muscles and in two proximal lower extremity muscles.

RESULTS

Conduction studies of the peroneal and sural nerves were normal (Table 1).

Table 2. Results of needle examination of the right upper and lower extremities

Muscle

Insertional activity

Spontaneous activity

Deltoid

Increased

1 + Fibs.

Biceps

Increased

2+ Fibs.

Triceps

Increased

I + Fibs.

FDI Gluteus medius Adductor longus

Increased Increased Increased

1 + Fibs. Occ. Fibs. 1+ Fibs.

Vastus medialis

Normal

None

Tibialis anterior

Increased

Occ. Fibs.

Medial gastroc.

Normal

None

Motor unit potentials Amplitude (mV)

Duration (ms)

Polyphasia

Recruitment

0.1-0.2 (0.2- 2.4) 0.3 (0.2- 1.5) 0.4-0.6 (0.3- 3.8) 0.4- 1 .O 1.o-2.0 1.o-2.0 (0.2- 1.9) 1 (0.3- 2.6) 0.5- 1.O (0.3- 2.5) 1.o-2.0 (0.3-3.1)

3 (5.6- 18.1) 3-5 (5.6-23.6) 4-6 (6.0- 17.4) 5-8 5-10 3-5 (3.8-31 -4) 5-8 (6.2-21.8) 3-5 (7.2-26.2) 3-4 (4.0- 15.9)

nl

Early

nl

Early

nl

Early

nl nl nl

Early Early Early

nl

Normal

nl

Normal

nl

Normal

Normal values for MUAP amplitude and duratfon are given /n parentheses (when available) below the observed values. nl = normal.

AAEM Case Report #22. Polymyositis

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311

CLINICAL COURSE

Biopsy of the left biceps revealed multiple large foci of interstitial lymphocytic infiltrates. There was associated degeneration and regeneration of myofibers with considerable variation in fiber size. Fiber necrosis was observed on muscle cross section, and on longitudinal section, segmental necrosis was noted in several areas. Endothelial hypertrophy was also seen in some areas. Fibrosis was minimal. She was then given the clinical diagnosis of overlap syndrome of systemic sclerosis with diffuse scleroderma and polyniyositis, since she had features of both diseases. Treatment was initiated with prednisone 40 mg/day and u-penicillamine 250 mg/day. u-Penicillamine was not tolerated due to rash, methotrexate was substituted. Within 4 months, the CK had dropped to 62 IU/L (nl < 80); SGOT, SGPT, and LDH all returned to normal. Strength increased slightly in the upper extremities and was essentially unchanged in the lower extremities. DISCUSSION

Polymyositis (PM) is characterized clinically by progressive muscle weakness, usually beginning in proximal muscles. Patients complain of difficulty arising from a chair, climbing stairs, and raising their arms above their head. Involvement of the pharyngeal striated musculature may lead to dysphagia. If untreated, respiratory muscles may also become involved. Cardiac involvement may be manifested by dysrhythmias, congestive heart failure, or pericarditis. Physical examination typically demonstrates proximal, more than distal, extremity weakness and occasional muscle tenderness. Muscle stretch reflexes and muscle bulk, however, are often maintained until late in the disease.” Creatine kinase (CK) is increased in the serum of 90% to 95% of patients with PM.97 Elevation of CK often precedes a clinical exacerbation of muscle weakness, and becomes normal before muscle strength improves ~linically.“~ Other muscle enzymes, including aldolase, SGOT, SGP‘I‘, and LDH may also be increased. Occasionally, patients with PM will present with an asymptomatic increase in CK.24 Bohan and Peter2 proposed five major criteria for the diagnosis of polymyositis-dermatomyositis (PM-DM) which are now commonly accepted. These include: (1) symmetrical proximal muscle weakness progressing over weeks to months; (2) muscle biopsy findings of degeneration, regeneration, necrosis, and interstitial mononuclear infil-

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AAEM Case Report #22: Polymyositis

tration; (3) elevation of serum skeletal muscle enzymes; (4)classic triad of EMG findings; and (5) typical skin rash of DM. The diagnosis of PM is felt to be definite if the first four criteria are met, probable if three are met, and possible if two are met. DM must also meet the fifth criterion. Polymyositis can be associated with dysimmune states, such as neoplasia, vasculitis, and other collagen vascular diseases (eg, systemic lupus erythematosus, scleroderma, rheumatoid arthritis, polyarteritis, and Sjogrens syndrome). It can be classified into subtypes accordingly.‘ Polymyositis has also been reported in association with human immunodeficiency virus (HIV) i n f e ~ t i 0 n . l ~ T h e earliest reports of electromyographic abnormalities in PM come from Buchthal and Pinelli5 Electromyographic examination of 1 1 patients with a histologically established diagnosis of PM revealed a significant decrease in the mean duration of MUAPs and an increase in the percentage of polyphasic MUAPs. In 1954, Lambert and colleagues” described electromyographic findings in 80 patients with PM. They reported a classic triad of findings including: (1) increased insertional activity with complex repetitive discharges, (2) fibrillations and positive sharp waves, and ( 3 ) small, polyphasic, short duration MUAPs recruited rapidly in relation to the strength of contraction. Myotonia has also been reported to occur in PM,14 but this is not a common finding. Motor and sensory nerve conduction studies are usually normal unless there is marked muscle atrophy, which can be associated with reduced M wave amplitudes. DeVere and Bradley” reported an 89% incidence of EMG abnormalities in a group of 98 patients with diagnoses ranging from possible to definite PM. Of the total, 45% had both abnormal spontaneous activity (fibrillations and positive sharp waves) and “myopathic” MUAP changes, while 44% had “myopathic” MUAP changes alone. The EMG was normal in 11% of patients. Bohan and colleagues4 studied the EMG in 122 patients with definite or probable PM or DM. Low amplitude, short duration, polyphasic MUAPs were seen in all 109 patients (89%) who had electromyographic abnormalities. Increased insertional activity, fibrillation potentials and positive sharp waves were described in 90 patients (74%), and complex repetitive discharges were found in 44 patients (36%).A completely normal EMG was described in 13 patients ( 1 1%). The yield of the electromyographic examina-

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'"

tion may be related to the number of muscles extronuclear) myopathy," Pompe's disease, and amined. Streib and colleague^^^) studied 40 pasome mitochondria1 myopathies.' tients with definite PM or DM examining at least 8 The electrical picture of PM changes as a result muscles in each patient. The incidence of EMG of treatment. The incidence of fibrillation potenabnormalities was reported as 100%; fibrillation tials, positive sharp waves, and complex repetitive potentials and "myopathic" MUAPs were reported discharges has been reported to decline after in at least one muscle in every patient. treatment with cortic~steroids,~ likely over several Polymyositis and DM appear to have a prediweeks." Bohan and Peter" reported that the earlilection for involvement of the paraspinal muscles; est electromyographic sign of improvement is the sometimes these are the only muscles involved disappearance of fibrillation potentials. In more both on EMG and biopsy. In the study by Streib chronic stages of the disease, MUAP changes and colleague^,^^) the incidence of fibrillation poevolve. Mechler"' studied 10 patients with PM, 9 tentials was highest in the paraspinal muscles proven by biopsy, 8 treated with steroids. In the (93%) followed by proximal extremity muscles acute phase, small, short-duration, polyphasic (64% to 76%). Bohan and colleagues4 reported MUAPs were observed. Chronically, up to 6 years 2/122 patients (1.6%) with electrophysiologic abafter diagnosis, large polyphasic MUAPs with innormalities limited to the paraspinal muscles. creased durations appeared in half the cases. The Mitz and colleague^'^ found that fibrillations most prominent changes were seen in those with were most prominent in the paraspinal muscles in the longest interval between initial diagnosis and 12 patients with biopsy-proven, definite PM. In EMG. Nakashima and colleagues35 found highone of these patients, EMG abnormalities as well amplitude, long-duration, MUAPs in 15 of 44 as changes on biopsy were limited to the paraspimuscles from patients with PM. These findings nal muscles. were most prominent in those patients with biopA number of other diseases may present with sies demonstrating interstitial myositis affecting connective tissue and vessels (7111 cases) and those electromyographic abnormalities similar to those with chronic parenchymatous lesions resulting in seen in PM and DM. Although a careful history primary degeneration of muscle fibers (8/24 and physical examination will often exclude a cases). number of these other entities, muscle biopsy is In 1975, Desmedt and Borenstein16 proposed often necessary to make a definitive diagnosis. Inthat fibrillation potentials could result from segclusion body myositis may have an identical EMG mental necrosis of muscle fibers "so that a distal picture, although some cases demonstrate a mixed population of large and small polyphasic units and fibre segment is separated from the part carrying the motor endplate." They performed myotomies some cases demonstrate striking distal involvein the biceps muscles of 7 baboons distal to the ment.g"L5 Acute toxic myopathies due to such zone of innervation and region of intramuscular causes as alcohol," c h l o r o q ~ i n e , 'hydroxychol~~~~ nerves. After 5 to 6 days, abundant fibrillations oroquine,20 p e n t a ~ o c i n eclofibrate,' ,~~ and epsilon were observed distal to the myotomy site. Kereshi amino-caproic may have an EMG picture and colleague^,^' however, found that 6 to 7 days similar to PM. Adult acid maltase deficiency may after crush injury or ligation of the semitendinosis appear similar to PM on EMG, but myotonic dismuscle in rats, no fibrillations were found. They charges are prominent in paraspinal muscles and also performed a myotomy on the brachiomdialis other proximal muscles. I 9 Chronic muscular dysmuscle of one of the authors: no fibrillations were trophies'" often demonstrate MUAP changes simobserved distally at 6 or 21 days. These authors ilar to those seen in myositis, although spontaneous activity is much less. The EMG in t r i c h i n o s i ~ ~ ~ suggested that the findings of Desmedt and Borenstein could have been due to partial denervareveals fibrillations and short duration, polyphasic tion of distal muscle fibers. MUAPs, but abnormalities may be scattered and T h e reduced average duration of MUAPs seen more prominent distally. Almost any myopathy, in acute PM has been attributed to loss of muscle except possibly thyroid toxic myopathy and stefibers in the periphery of the motor unit.* Slow roid myopathy may be associated with some deinitial and terminal components of the MUAP, gree of spontaneous activity. The appearance of which are normally recorded from peripheral fibotulism by EMG examination may demonstrate bers more than 0.5 mm from the electrode, are reextremely small, polyphasic MUAPs, associated duced in amplitude or absent, making the MUAP with fibrillations.21 In children, the EMG appearappear shorter in duration. This notion has been ance of PM may also be seen in myotubular (cen-

AAEM Case Report #22: Polymyositis

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313

countered by reports that the motor unit territory can actually be increased in PM.'333' The amplitude of MUAPs may also not be uniformly reduced in PM as shown by the work of Trojaborg4' and M e ~ h l e r . ~ * The increased polyphasia has been attributed to not only muscle fiber loss, but also to the consequences of reinnervation of denervated muscle fib e r ~ The . ~ ~lack of polyphasicity in this case may be related to the recent onset of symptoms. The EMG was performed only 2 months after the onset of symptoms, likely too soon for the effects of muscle fiber reinnervation to be seen. Electrodiagnostic studies are, therefore, a key

component in the evaluation of the patient with suspected myositis. Electrodiagnostic studies are useful in excluding neurogenic disorders, as well as other myopathies that may look like myositis clinically. Since needle electromyography can result in artifacts on muscle biopsy, studies should generally be limited to one side. The electromyographer can help in directing the biopsy by suggesting a muscle with moderate active findings contralateral to the side studied. As previously mentioned, spontaneous activity is reduced with appropriate treatment. Therefore, follow-up electrodiagnostic studies may be used to help assess the adequacy of treatment.

REFERENCES 1. Abourizk N, Abu Khalil B, Bahuth N, Afifi AK: Clofibrateinduced muscular syndrome: Report of a case with clinical, electromyographic, and pathologic observations. J Neurol Sci 1979; 42:l. 2. Bohan A, Peter JB: Polymyositis and dermatomyositis. N Engl J Med 1975; 292:344-347. 3. Bohan A, Peter JB: Polymyositis and dermatomyositis. N Engl J Med 1975; 292:403-407. 4. Bohan A, Peter JB, Bowman RL, Pearson CM: A computer assisted analysis of 153 patients with polymyositis and dermatomyositis. Medicine 1977; 56:255-286. 5. Buchthal F, Pinelli P: Muscle action potentials in polymyositis. Neurology 1953; 3:424-436. 6. Buchthal F, Rosenfalk P: Action potential parameters in different human muscles. Acta Psychiatr Scand 1955; 30: 125. 7. Buchthal F: Electrophysiological signs of myopathy as related to muscle biopsy. Acta Neurol 1977; 32:l-29. 8. Buchthal F: Electromyography in the evaluation of muscle diseases. Neurol Clin 1985; 3:573-598. 9. Carpenter S, Karpati G, Heller I, Eisen A: Inclusion body myositis: A distinct variety of idiopathic inflammatory myopathy. Neurology 1978; 28:8- 17. 10. Chu-Andrews J, Johnson RJ: Ebctrodiagnosis, a n Anatomical and Clinical Approach. Philadelphia, J.B. Lippincott Co., 1986, p p 230-235. 11. Cornelio F, Di Donato S, Peluchetti D, et al: Fatal cases of lipid storage myopathy with carnitine deficiency. J Neurol Neurosurg Psychiatry 1977; 40: 170. 12. Cronin ME, Miller FW, Plotz PH: Polymyositis and dermatomyositis, in Schumacher HR (ed): Primer on the Rheumatic Disease. Atlanta, Arthritis Foundation, 1988, p p 120123. 13. Daube JR: Electrodiagnosis of muscle disorders, in Engel AG, Banker BQ (eds): Myology. New York, McGraw-Hill, 1986, p p 1081-1121. 14. Daube JR: AAEE minimonograph #11: Needle Examination in Electromyography. Rochester, MN, American Association of Electromyography and Electrodiagnosis, 1979. 15. Dalakas MC, Pezeshkpour GH: Neuromuscular diseases associated with human immunodeficiency virus infection. A n n Neurol 1988; 23:S38-S48. 16. Desmedt JE, Borenstein S: Relationship of spontaneous fibrillation potentials to muscle fibre segmentation in human muscular dystrophy. Nature 1975; 258:531-534. 17. DeVere R, Bradley WG: Polymyositis: Its presentation, morbidity and mortality. Brain 1975; 98:637-666. 18. DiMauro S, Hartwig GB, Hays A, et al: Debrancher defi-

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ciency: Neuromuscular disorder in 5 adults. A n n Neurol 1979; 5:422. 19. Engel AG, Gomez MR, Seybold ME, Lambert EH: The spectrum and diagnosis of acid maltase deficiency. Neurology (Minneap) 1975; 23:95. 20. Estes ML, Ewing-Wilson D, Chou SM, Mitsumoto H, Hanson M, Shirey E, Ratliff NB: Chloroquine neuromyotoxicity. Clinical and pathological perspective. Am J Med 1987; 82:447-455. 21. Gutmann L, Pratt L: Pathophysiologic aspects of human botulism. Arch Neurol 1976; 33: 175. 22. Hawkes CH, Absolon MJ: Myotubular myopathy associated with cataract and electrical myotonia. J Neurol Neurosurg Psychiatry 1975; 41:761. 23. Henriksson J , Stalberg E: The terminal innervation pattern in polymyositis: A histochemical and SFEMG study. Muscle Nerve 1978; 1:3- 13. 24. Joy JL, Oh SJ: Asymptomatic hyper-CK-emia: An electrophysiologic and histopathologic study. Muscle Nerve 1989; 12x206- 209. 25. Julien J , Vital CL, Vallat JM, Lagueny A, Sapina D: Inclusion body myositis: Clinical, biological, and ultrastructural study. J Neurol Sci 1982; 55:15-24. 26. Kane MJ, Silverman LR, Rand J H , Paciucci PA, Holland JF: Myonecrosis as a complication of the use of epsilon amino-caproic acid: A case report and review of the literature. A m J Med 1988; 85:861-863. 27. Kereshi S, McComas A, Kowalchuk N, Stuart A: Absence of fibrillation after muscle injury. Exp Neurol 1983; 80:645-651. 28. Kimura J: Electrodiagnosis in Diseases of Nerve and Muscle: Principles and Practice. Philadelphia, F.A. Davis, 1983, pp 128- 133, 267-285, 540. 29. Lambert EH, Sayre GP, Eaton LM: Electrical activity of muscle in polymyositis. Trans Am Neurol Assoc 1954; 79:6469. 30. Layzer RE, Lovelace RE, Rowland LP: Hyperkalemic periodic paralysis. Arch Neurol 1967; 16:455. 31. MacKay AR, Sang UH, Weinstein PR: Myopathy associated with epsilon amino-caproic acid (EACA) therapy. Report of two cases. J Neurosurg 1978; 49:597-601. 32. Mechler F: Changing electromyographic findings during the chronic course of polymyositis. J Neurol Sci 1974; 231237-242. 33. Medsger TA, Dawson WN, Masi AT: T h e epidemiology of polymyositis. Am J Med 1970; 48:715-723. 34. Mitz M, Chang GJ, Albers JW, Sulaiman AR: Electromyographic and histologic paraspinal abnormalities in polyniy-

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ositddermatomyositis. Arch Phys Med Rehabil 1981; 62: 118- 121. Nakashima K, Tabuchi Y, Takahashi K: T h e diagnostic significance of large action potentials in myopathy. J Neurol Sci 1983; 61:161-170. Oh SJ, Rollins JL, Lewis I: Pentazocine-induced fibrous myopathy. J A M A 1975; 231:271. Pearson CM, Bohan A: T h e spectrum of polymyositis and derrnatomyositis. Med Clin North Am 1977; 61 :439-457. Perkoff GT, Dioso MM, Bleisch V, Klinkerfuss F: A spectrum of myopathy associated with alcoholism. I. Clinical and laboratory features. Ann Intern Med 1967; 67:48 1,

AAEM Case Report #22: Polymyositis

39. Sacco G, Buchthal F, Rosenfalk P: Motor unit potentials at different ages. Arch Neurol 1962; 6:366-373. 40. Streib EW, Wilbourn A J , Mitsumoto H: Spontaneous electrical muscle fiber activity in polymyositis and derniatomyositis. Muscle Nenie 1979; 2: 14- 18. C h i Nuu4 1. Trojaborg W: EMG in myositis. Elrctrocncc~i/ialo~rophysiol 1987; 665105-S 106. 42. Waylonis GW, Johnson EW: T h e electromyogram in acute trichinosis: Report of four cases. Arch Phys Med Krhubil 1964; 45:177. 43. Whisnant J P , Espinosa RE, Kierland RR, Lambert EH: Chloroquine neuromyopathy. Muyo Clzn Proc 1963; 38:501.

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AAEM case report #22: polymyositis.

Polymyositis usually presents with progressive proximal muscle weakness, increased serum levels of muscle enzymes, inflammatory changes on muscle biop...
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