Articles
Sensitivity and specificity of threshold tracking transcranial magnetic stimulation for diagnosis of amyotrophic lateral sclerosis: a prospective study Parvathi Menon, Nimeshan Geevasinga, Con Yiannikas, James Howells, Matthew C Kiernan, Steve Vucic
Summary Lancet Neurol 2015; 14: 478–84 Published Online April 3, 2015 http://dx.doi.org/10.1016/ S1474-4422(15)00014-9 This online publication has been corrected. The corrected version first appeared at thelancet.com/ neurology on April 14, 2015 See Comment page 457 Derek Craig Motor Neuron Disease Research Centre, Western Clinical School (P Menon PhD, N Geevasinga MBBS, Prof S Vucic PhD), and Department of Neurology (Prof S Vucic), Westmead Hospital, Westmead, Royal North Shore Hospital (C Yiannikas MBBS), and Brain and Mind Research Institute, Royal Prince Alfred Hospital (J Howells PhD, Prof M C Kiernan DSc), University of Sydney, NSW, Australia Correspondence to: Prof Steve Vucic, Department of Neurology, Westmead Hospital, Westmead, NSW 2145, Australia [email protected]
Background Diagnosis of amyotrophic lateral sclerosis (ALS) remains problematic, with substantial diagnostic delays. We assessed the sensitivity and specificity of a threshold tracking transcranial magnetic stimulation (TMS) technique, which might allow early detection of upper motor neuron dysfunction, for the diagnosis of the disorder. Methods We did a prospective study of patients referred to three neuromuscular centres in Sydney, Australia, in accordance with the Standards for Reporting of Diagnostic Accuracy. Participants had definite, probable, or possible ALS, as defined by the Awaji criteria; or pure motor disorder with clinical features of upper and lower motor neuron dysfunction in at least one body region, progressing over a 6 month follow-up period; or muscle wasting and weakness for at least 6 months. All patients underwent threshold tracking TMS at recruitment (index test), with application of the reference standard, the Awaji criteria, to differentiate patients with ALS from those with non-ALS disorders. The investigators who did the index test were masked to the results of the reference test and all other investigations. The primary outcome measures were the sensitivity and specificity of TMS in differentiating ALS from non-ALS disorders; these measures were derived from receiver operator curve analysis. Findings Between Jan 1, 2010, and March 1, 2014, we screened 333 patients; 281 met our inclusion criteria. We eventually diagnosed 209 patients with ALS and 68 with non-ALS disorders; the diagnosis of four patients was inconclusive. The threshold tracking TMS technique differentiated ALS from non-ALS disorders with a sensitivity of 73·21% (95% CI 66·66–79·08) and specificity of 80·88% (69·53–89·40) at an early stage in the disease. All patients tolerated the study well, and we did not record any adverse events from performance of the index test. Interpretation The threshold tracking TMS technique reliably distinguishes ALS from non-ALS disorders and, if these findings are replicated in larger studies, could represent a useful diagnostic investigation when combined with the Awaji criteria to prove upper motor neuron dysfunction at early stages of ALS. Funding Motor Neuron Disease Research Institute of Australia, National Health and Medical Research Council of Australia, and Pfizer.
Introduction Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and invariably fatal neurodegenerative disorder of the upper motor neurons (UMNs) and lower motor neurons (LMNs).1 Diagnosis of the disease relies on identification of concurrent UMN and LMN dysfunction, with the level of diagnostic certainty dependent on the extent of UMN and LMN dysfunction.1–3 The clinically based ALS El Escorial criteria are deemed to be insensitive, particularly in early stages of the disease or for atypical phenotypes, potentially resulting in substantial diagnostic delays.4 Consequently, creation of adequate management strategies, including commencement of treatments such as riluzole, and recruitment into therapeutic trials, might be delayed, perhaps beyond the therapeutic time window.5 Despite rapidly evolving interest in ALS clinical trial methodology, the process of diagnosis remains complex. The first international workshop that aimed to reach a consensus on the definition of ALS diagnosis was held in El Escorial (Madrid, Spain) in 1990.6 Since then, many revisions and new approaches have appeared,2 including
478
the most recent neurophysiologically based Awaji criteria.3 These criteria proposed that neurophysiological features of LMN dysfunction, as indicated by chronic neurogenic changes, fibrillation potentials or positive sharp waves, and fasciculations, were equivalent to clinical features of LMN dysfunction. Although the Awaji criteria had a higher sensitivity than the revised El Escorial criteria,7–14 the diagnostic benefit seemed most prominent in patients with bulbar-onset disease.7 Additionally, the clinically probable laboratory-supported diagnostic category was abolished in the Awaji criteria, thereby necessitating identification of signs of UMN dysfunction in two regions to establish a diagnosis of ALS. In view of the difficulties with identification of UMN signs in ALS,15 the sensitivity of the Awaji criteria might be lower than that of the revised El Escorial criteria.11 The functional integrity of the UMN system in ALS can be objectively assessed by transcranial magnetic stimulation (TMS) techniques.16 Evidence from animal and human studies has established that TMS assesses UMN function, with neuronal activation mediated by specific ion channels www.thelancet.com/neurology Vol 14 May 2015
Articles
and synaptic processes acting via different neurotransmitter systems.16,17 One threshold tracking TMS technique18 that overcomes the motor-evoked potential (MEP) amplitude variability that is evident with conventional TMS techniques has established cortical hyperexcitability as a specific and early feature of ALS, differentiating the disease from mimic neuromuscular disorders.19 Importantly, cortical hyperexcitability has been postulated to progress to normal excitability or hypoexcitability during the course of the disease.16 Although diagnostic value of threshold tracking TMS was reported in one study,19 the testing was not done in accordance with the Standards for Reporting of Diagnostic Accuracy (STARD) and was limited to one centre. As such, generalisability of the results could not be definitively assessed.20 The aim of the present study was to establish diagnostic accuracy of the threshold tracking TMS technique in differentiation of ALS from mimic neuromuscular disorders. To avoid potential bias and ensure wide applicability of the findings, we recruited patients across three neuromuscular clinics in accordance with STARD criteria.
Methods Study design and patients In this prospective study, we recruited patients from three neuromuscular centres in Sydney, Australia. All patients underwent detailed clinical assessment and grading before enrolment, including electrodiagnostic investigations. We recruited patients prospectively and consecutively in keeping with the inclusion criteria. The study population consisted of patients with suspected ALS, although none of the patients had been diagnosed with the disease before recruitment. Inclusion criteria were as follows: definite, probable, or possible ALS, as defined by the Awaji criteria;3 pure motor disorder with clinical features of UMN and LMN dysfunction in separate body regions, where LMN dysfunction developed caudal to UMN dysfunction, with evidence of disease progression during a follow-up period of 6 months from initial assessment; or a neuromuscular disorder mimicking ALS, defined as muscle weakness and wasting for at least 6 months. At the time of assessment, we did not know that these patients would be classified in the non-ALS group. Exclusion criteria were as follows: pure UMN syndrome for which laboratory and neuroimaging studies suggested a diagnosis other than possible ALS; history of acute migraine headaches in the 4 weeks preceding recruitment, because migraine can increase cortical excitability; use of drugs that could affect TMS variables; history of head trauma, movement disorder, epilepsy, stroke, or transient ischaemic attack; presence of a pacemaker or other cardiac devices, cochlear implants, or previous brain surgery, such as clipping of a cerebral aneurysm; and inability to tolerate TMS testing, or marked wasting of the thenar eminence precluding recording of motor responses. All patients provided written informed consent www.thelancet.com/neurology Vol 14 May 2015
for the procedures, which were approved by the Western Sydney Local Health District and South East Sydney Area Health Service Human Research Ethics Committees.
Masking All patients underwent threshold tracking TMS at recruitment, done by two examiners (PM and NG) who had neurology training and experience with neurophysiological techniques. At the time of the index test, these examiners were masked to the results of the reference test and all other investigations, and the clinical history of each patient. Data analysis was done by a separate rater (SV) with experience in the analysis of the results of the index test and reference standard.
Procedures We used the Awaji diagnostic criteria as the reference standard.3 We did the study in accordance with the STARD criteria and applied the index test and reference standard to all patients at the time of recruitment. We clinically staged patients with ALS using the Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R) score.21 We recorded disease duration (in months) from time of symptom onset, and site of disease onset. We assessed muscle strength using the Medical Research Council score, with the following muscle groups assessed: shoulder abduction, elbow flexion and extension, wrist dorsiflexion, finger abduction and thumb abduction, hip flexion, knee extension, and ankle dorsiflexion (all bilaterally), yielding a maximum score of 90. We assessed and graded UMN function with a dedicated UMN score.22 We did the TMS investigation according to a previously reported technique,18 using a 90 mm circular coil. Briefly, we fixed the MEP amplitude and measured changes in the test stimulus intensity needed to generate a target response of 0·2 mV (with a 20% allowance above and below) when preceded by a subthreshold conditioning stimulus. We recorded MEP response over the right abductor pollicis brevis muscle. We defined resting motor threshold as the stimulus intensity needed to maintain this target MEP response. We did paired-pulse threshold tracking to establish short-interval intracortical inhibition (SICI) and intracortical facilitation, whereas we used single-pulse TMS to establish the MEP amplitude (in mV), cortical silent period duration (in ms), and central motor conduction time, according to a previously reported technique.18 In patients with severe wasting of the thenar eminence, as assessed clinically or with nerveconduction studies disclosing a median nerve compound muscle section potential of less than 1 mV, we did not do cortical excitability testing.
Outcomes The primary outcome measures were the diagnostic sensitivity and specificity of TMS in differentiating 479
Articles
ALS from non-ALS mimic disorders. Secondary outcome measures were diagnostic accuracy of TMS in ALS subgroups defined by use of the Awaji criteria (definite, probable, or possible), site of disease onset (bulbar vs limb), phenotype (presence or absence of signs of UMN dysfunction), and treatment (riluzole vs non-riluzole).
333 consecutive patients assessed for eligibility
52 excluded 31 pure UMN syndrome with diagnosis other than possible ALS 21 marked muscle wasting precluding recording of motor responses
Statistical analysis We used receiver operator curve analysis to assess the diagnostic accuracy of the index test. We established the sensitivity, specificity, positive and negative likelihood ratios, and diagnostic odds ratio for threshold tracking TMS. Additionally, we calculated the number needed to test to be able to diagnose one extra case of ALS with TMS when applied to a group of patients with neuromuscular disorders, according to the formula reported by Bandolier.23 We used multiple regression analysis to assess whether the outcome variables (SICI reduction and motor cortex inexcitability) were affected by independent variables. We deemed a probability value of less than 0·05 to be significant. We used SPSS version 21 for all analyses.
Role of the funding source The funders of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report. All authors had full access to all the data in the study and the corresponding author had final responsibility for the decision to submit for publication.
281 enrolled
281 underwent reference test
281 underwent index test
Results 167 tested positive (hyperexcitable or inexcitable motor cortex)
114 tested negative (normal motor cortical excitability)
1 inconclusive (based on reference test)
153 ALS 13 non-ALS
3 inconclusive (based on reference test)
56 ALS 55 non-ALS
Figure 1: Flow diagram of study After the index test, results were sorted on the basis of the reference standard (the Awaji criteria). ALS=amyotrophic lateral sclerosis. TMS=transcranial magnetic stimulation. UMN=upper motor neuron. Amyotrophic lateral sclerosis (n=209) Mean age at assessment (years) Men (%)
59·9 (14·5) 125 (60%)
Women (%)
84 (40%)
Mean disease duration (months)
16·7 (15·9)
ALSFRS-R
41 (38–44)
Median total MRC score
82 (79–88)
Mimic neuromuscular disorders (n=68) 48·4 (15·7) 45 (66%) 23 (34%) 102·1 (13·6) ·· 87 (84–88)
Median upper limb MRC score
57 (51–60)
57 (56–60)
Median lower limb MRC score
30 (26–30)
30 (28–30)
Upper motor neuron score
12 (10–13)
0
Data are mean (SD), n (%), or median (IQR). MRC=Medical Research Council. ALSFRS-R=amyotrophic lateral sclerosis functional rating score-revised.
Table 1: Demographic features of patients with amyotrophic lateral sclerosis and neuromuscular disorders mimicking amyotrophic lateral sclerosis
480
Between Jan 1, 2010, and March 1, 2014, we screened 333 patients (206 men and 127 women; mean age 57·6 years [SD 14·6]), 281 (84%) of whom met the inclusion criteria and were therefore enrolled (figure 1). 209 patients were eventually diagnosed with ALS. Of these, we classified 109 (52%) as Awaji definite or probable and 46 (22%) as Awaji possible. 54 (26%) patients did not meet Awaji criteria at initial assessment, although most progressed during followup, leading to reclassification into the Awaji definite or probable group (201 [96%]). Two patients did not progress appreciably and remained Awaji negative, eventually being diagnosed with primary muscular atrophy. 21 (6%) of the 333 patients screened could not undergo TMS testing because of marked hand weakness. We diagnosed 68 patients with non-ALS mimic disorders (table 1, figure 1), who served as pathological controls. Muscle strength, as measured by the Medical Research Council score, was similar between groups. The ALSFRS-R scores indicated a mild level of dysfunction in the ALS cohort. Patients in the non-ALS cohort were younger than patients with ALS. Threshold tracking TMS reliably differentiated ALS from non-ALS disorders (figure 2). Reduction of averaged SICI (interstimulus interval 1–7 ms) seemed to be the most robust variable for differentiation of ALS from non-ALS, with an area under the curve of 0·80 (95% CI 0·75–0·85; figure 3), showing “very good” diagnostic utility. The remainder of the TMS variables had lower diagnostic utility than did averaged SICI, as shown by lower area under the curve, including reduced peak SICI at an interstimulus interval of 3 ms (0·78 [95% CI 0·72–0·84]), reduced cortical silent period duration (0·73 [0·64–0·79]), increased intracortical facilitation (0·62 www.thelancet.com/neurology Vol 14 May 2015
Articles
[0·54–0·68]), increased MEP amplitude (0·56 [0·50–0·65]), reduced resting motor threshold (0·51 [0·50–0·58]), and extended central motor conduction time (0·50 [0·50–0·54). Consequently, we defined a positive index test as either a reduction of averaged SICI (less than 5·5%, as previously reported)19 or inexcitable motor cortex (defined as a resting motor threshold of more than 95% of A 30
ALS Non-ALS
Threshold change (%)
20
10
0
–10
–20
B 30
Threshold change (%)
20
10
0
–10
–20 0
10
20
30
maximum stimulator output).24 With these diagnostic variables, the threshold tracking TMS technique had a sensitivity of 73·21% (95% CI 66·66–79·08) and a specificity of 80·88% (69·53–89·40; table 2). Of the 56 patients with ALS showing a negative index test, defined as short-interval intracortical inhibition of more than 5·5% and absence of motor cortex inexcitability, 25 (45%) were classified as Awaji possible or not meeting criteria (did not initially meet criteria but were later diagnosed with ALS), whereas 31 (55%) were classified as Awaji definite or probable ALS. All patients tolerated the study well; none stopped testing due to intolerance and there were no adverse events. We recorded no adverse events from performance of the index test. Subgroup analysis showed a similar area under the curve between patients with definite or probable ALS (0·79 [95% CI 0·72–0·86]) and those with possible ALS or not meeting criteria (0·83 [0·76–0·89]). Additionally, sensitivity and specificity of threshold tracking TMS was similar between groups (table 2). Mean time between TMS assessment and progression to ALS diagnosis, as defined by the Awaji definite or probable category, was 15·8 months (SD 2·0). An extra 34% of patients with ALS could be diagnosed at initial assessment with use of threshold tracking TMS abnormalities compared with use of the Awaji criteria alone. The sensitivity of the threshold tracking TMS technique was similar between patients with ALS classified as not meeting criteria (72·22% [95% CI 58·35–83·54]) and the Awaji possible group (77·08% [62·68–87·95]; p=0·42). We noted no significant difference in the sensitivity of the threshold tracking TMS technique between patients with signs of UMN dysfunction (UMN score of 3 or more; 74·0% [95% CI 66·28–80·56]) and those without UMN signs (UMN score of less than 3; 65·22% [42·47–83·58];
Insterstimulus interval (ms) 1·0
C 15
10
Sensitivity
Mean SICI, 1–7 ms (%)
0·8
0·6
0·4
Averaged SICI (ISI 1–7 ms) Peak SICI (ISI 3 ms) CSP duration ICF MEP amplitude RMT CMCT
5 0·2
0 ALS
Non-ALS
Figure 2: SICI in patients with ALS and mimic neuromuscular disorders SICI is shown in (A) one patient with ALS and one with a non-ALS mimic disorder (facial-onset sensory motor neuropathy), and (B, C) all patients. ALS=amyotrophic lateral sclerosis. SICI=short-interval intracortical inhibition. Error bars are SEs. p
Sensitivity and specificity of threshold tracking transcranial magnetic stimulation for diagnosis of amyotrophic lateral sclerosis: a prospective study Parvathi Menon, Nimeshan Geevasinga, Con Yiannikas, James Howells, Matthew C Kiernan, Steve Vucic
Summary Lancet Neurol 2015; 14: 478–84 Published Online April 3, 2015 http://dx.doi.org/10.1016/ S1474-4422(15)00014-9 This online publication has been corrected. The corrected version first appeared at thelancet.com/ neurology on April 14, 2015 See Comment page 457 Derek Craig Motor Neuron Disease Research Centre, Western Clinical School (P Menon PhD, N Geevasinga MBBS, Prof S Vucic PhD), and Department of Neurology (Prof S Vucic), Westmead Hospital, Westmead, Royal North Shore Hospital (C Yiannikas MBBS), and Brain and Mind Research Institute, Royal Prince Alfred Hospital (J Howells PhD, Prof M C Kiernan DSc), University of Sydney, NSW, Australia Correspondence to: Prof Steve Vucic, Department of Neurology, Westmead Hospital, Westmead, NSW 2145, Australia [email protected]
Background Diagnosis of amyotrophic lateral sclerosis (ALS) remains problematic, with substantial diagnostic delays. We assessed the sensitivity and specificity of a threshold tracking transcranial magnetic stimulation (TMS) technique, which might allow early detection of upper motor neuron dysfunction, for the diagnosis of the disorder. Methods We did a prospective study of patients referred to three neuromuscular centres in Sydney, Australia, in accordance with the Standards for Reporting of Diagnostic Accuracy. Participants had definite, probable, or possible ALS, as defined by the Awaji criteria; or pure motor disorder with clinical features of upper and lower motor neuron dysfunction in at least one body region, progressing over a 6 month follow-up period; or muscle wasting and weakness for at least 6 months. All patients underwent threshold tracking TMS at recruitment (index test), with application of the reference standard, the Awaji criteria, to differentiate patients with ALS from those with non-ALS disorders. The investigators who did the index test were masked to the results of the reference test and all other investigations. The primary outcome measures were the sensitivity and specificity of TMS in differentiating ALS from non-ALS disorders; these measures were derived from receiver operator curve analysis. Findings Between Jan 1, 2010, and March 1, 2014, we screened 333 patients; 281 met our inclusion criteria. We eventually diagnosed 209 patients with ALS and 68 with non-ALS disorders; the diagnosis of four patients was inconclusive. The threshold tracking TMS technique differentiated ALS from non-ALS disorders with a sensitivity of 73·21% (95% CI 66·66–79·08) and specificity of 80·88% (69·53–89·40) at an early stage in the disease. All patients tolerated the study well, and we did not record any adverse events from performance of the index test. Interpretation The threshold tracking TMS technique reliably distinguishes ALS from non-ALS disorders and, if these findings are replicated in larger studies, could represent a useful diagnostic investigation when combined with the Awaji criteria to prove upper motor neuron dysfunction at early stages of ALS. Funding Motor Neuron Disease Research Institute of Australia, National Health and Medical Research Council of Australia, and Pfizer.
Introduction Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and invariably fatal neurodegenerative disorder of the upper motor neurons (UMNs) and lower motor neurons (LMNs).1 Diagnosis of the disease relies on identification of concurrent UMN and LMN dysfunction, with the level of diagnostic certainty dependent on the extent of UMN and LMN dysfunction.1–3 The clinically based ALS El Escorial criteria are deemed to be insensitive, particularly in early stages of the disease or for atypical phenotypes, potentially resulting in substantial diagnostic delays.4 Consequently, creation of adequate management strategies, including commencement of treatments such as riluzole, and recruitment into therapeutic trials, might be delayed, perhaps beyond the therapeutic time window.5 Despite rapidly evolving interest in ALS clinical trial methodology, the process of diagnosis remains complex. The first international workshop that aimed to reach a consensus on the definition of ALS diagnosis was held in El Escorial (Madrid, Spain) in 1990.6 Since then, many revisions and new approaches have appeared,2 including
478
the most recent neurophysiologically based Awaji criteria.3 These criteria proposed that neurophysiological features of LMN dysfunction, as indicated by chronic neurogenic changes, fibrillation potentials or positive sharp waves, and fasciculations, were equivalent to clinical features of LMN dysfunction. Although the Awaji criteria had a higher sensitivity than the revised El Escorial criteria,7–14 the diagnostic benefit seemed most prominent in patients with bulbar-onset disease.7 Additionally, the clinically probable laboratory-supported diagnostic category was abolished in the Awaji criteria, thereby necessitating identification of signs of UMN dysfunction in two regions to establish a diagnosis of ALS. In view of the difficulties with identification of UMN signs in ALS,15 the sensitivity of the Awaji criteria might be lower than that of the revised El Escorial criteria.11 The functional integrity of the UMN system in ALS can be objectively assessed by transcranial magnetic stimulation (TMS) techniques.16 Evidence from animal and human studies has established that TMS assesses UMN function, with neuronal activation mediated by specific ion channels www.thelancet.com/neurology Vol 14 May 2015
Articles
and synaptic processes acting via different neurotransmitter systems.16,17 One threshold tracking TMS technique18 that overcomes the motor-evoked potential (MEP) amplitude variability that is evident with conventional TMS techniques has established cortical hyperexcitability as a specific and early feature of ALS, differentiating the disease from mimic neuromuscular disorders.19 Importantly, cortical hyperexcitability has been postulated to progress to normal excitability or hypoexcitability during the course of the disease.16 Although diagnostic value of threshold tracking TMS was reported in one study,19 the testing was not done in accordance with the Standards for Reporting of Diagnostic Accuracy (STARD) and was limited to one centre. As such, generalisability of the results could not be definitively assessed.20 The aim of the present study was to establish diagnostic accuracy of the threshold tracking TMS technique in differentiation of ALS from mimic neuromuscular disorders. To avoid potential bias and ensure wide applicability of the findings, we recruited patients across three neuromuscular clinics in accordance with STARD criteria.
Methods Study design and patients In this prospective study, we recruited patients from three neuromuscular centres in Sydney, Australia. All patients underwent detailed clinical assessment and grading before enrolment, including electrodiagnostic investigations. We recruited patients prospectively and consecutively in keeping with the inclusion criteria. The study population consisted of patients with suspected ALS, although none of the patients had been diagnosed with the disease before recruitment. Inclusion criteria were as follows: definite, probable, or possible ALS, as defined by the Awaji criteria;3 pure motor disorder with clinical features of UMN and LMN dysfunction in separate body regions, where LMN dysfunction developed caudal to UMN dysfunction, with evidence of disease progression during a follow-up period of 6 months from initial assessment; or a neuromuscular disorder mimicking ALS, defined as muscle weakness and wasting for at least 6 months. At the time of assessment, we did not know that these patients would be classified in the non-ALS group. Exclusion criteria were as follows: pure UMN syndrome for which laboratory and neuroimaging studies suggested a diagnosis other than possible ALS; history of acute migraine headaches in the 4 weeks preceding recruitment, because migraine can increase cortical excitability; use of drugs that could affect TMS variables; history of head trauma, movement disorder, epilepsy, stroke, or transient ischaemic attack; presence of a pacemaker or other cardiac devices, cochlear implants, or previous brain surgery, such as clipping of a cerebral aneurysm; and inability to tolerate TMS testing, or marked wasting of the thenar eminence precluding recording of motor responses. All patients provided written informed consent www.thelancet.com/neurology Vol 14 May 2015
for the procedures, which were approved by the Western Sydney Local Health District and South East Sydney Area Health Service Human Research Ethics Committees.
Masking All patients underwent threshold tracking TMS at recruitment, done by two examiners (PM and NG) who had neurology training and experience with neurophysiological techniques. At the time of the index test, these examiners were masked to the results of the reference test and all other investigations, and the clinical history of each patient. Data analysis was done by a separate rater (SV) with experience in the analysis of the results of the index test and reference standard.
Procedures We used the Awaji diagnostic criteria as the reference standard.3 We did the study in accordance with the STARD criteria and applied the index test and reference standard to all patients at the time of recruitment. We clinically staged patients with ALS using the Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R) score.21 We recorded disease duration (in months) from time of symptom onset, and site of disease onset. We assessed muscle strength using the Medical Research Council score, with the following muscle groups assessed: shoulder abduction, elbow flexion and extension, wrist dorsiflexion, finger abduction and thumb abduction, hip flexion, knee extension, and ankle dorsiflexion (all bilaterally), yielding a maximum score of 90. We assessed and graded UMN function with a dedicated UMN score.22 We did the TMS investigation according to a previously reported technique,18 using a 90 mm circular coil. Briefly, we fixed the MEP amplitude and measured changes in the test stimulus intensity needed to generate a target response of 0·2 mV (with a 20% allowance above and below) when preceded by a subthreshold conditioning stimulus. We recorded MEP response over the right abductor pollicis brevis muscle. We defined resting motor threshold as the stimulus intensity needed to maintain this target MEP response. We did paired-pulse threshold tracking to establish short-interval intracortical inhibition (SICI) and intracortical facilitation, whereas we used single-pulse TMS to establish the MEP amplitude (in mV), cortical silent period duration (in ms), and central motor conduction time, according to a previously reported technique.18 In patients with severe wasting of the thenar eminence, as assessed clinically or with nerveconduction studies disclosing a median nerve compound muscle section potential of less than 1 mV, we did not do cortical excitability testing.
Outcomes The primary outcome measures were the diagnostic sensitivity and specificity of TMS in differentiating 479
Articles
ALS from non-ALS mimic disorders. Secondary outcome measures were diagnostic accuracy of TMS in ALS subgroups defined by use of the Awaji criteria (definite, probable, or possible), site of disease onset (bulbar vs limb), phenotype (presence or absence of signs of UMN dysfunction), and treatment (riluzole vs non-riluzole).
333 consecutive patients assessed for eligibility
52 excluded 31 pure UMN syndrome with diagnosis other than possible ALS 21 marked muscle wasting precluding recording of motor responses
Statistical analysis We used receiver operator curve analysis to assess the diagnostic accuracy of the index test. We established the sensitivity, specificity, positive and negative likelihood ratios, and diagnostic odds ratio for threshold tracking TMS. Additionally, we calculated the number needed to test to be able to diagnose one extra case of ALS with TMS when applied to a group of patients with neuromuscular disorders, according to the formula reported by Bandolier.23 We used multiple regression analysis to assess whether the outcome variables (SICI reduction and motor cortex inexcitability) were affected by independent variables. We deemed a probability value of less than 0·05 to be significant. We used SPSS version 21 for all analyses.
Role of the funding source The funders of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report. All authors had full access to all the data in the study and the corresponding author had final responsibility for the decision to submit for publication.
281 enrolled
281 underwent reference test
281 underwent index test
Results 167 tested positive (hyperexcitable or inexcitable motor cortex)
114 tested negative (normal motor cortical excitability)
1 inconclusive (based on reference test)
153 ALS 13 non-ALS
3 inconclusive (based on reference test)
56 ALS 55 non-ALS
Figure 1: Flow diagram of study After the index test, results were sorted on the basis of the reference standard (the Awaji criteria). ALS=amyotrophic lateral sclerosis. TMS=transcranial magnetic stimulation. UMN=upper motor neuron. Amyotrophic lateral sclerosis (n=209) Mean age at assessment (years) Men (%)
59·9 (14·5) 125 (60%)
Women (%)
84 (40%)
Mean disease duration (months)
16·7 (15·9)
ALSFRS-R
41 (38–44)
Median total MRC score
82 (79–88)
Mimic neuromuscular disorders (n=68) 48·4 (15·7) 45 (66%) 23 (34%) 102·1 (13·6) ·· 87 (84–88)
Median upper limb MRC score
57 (51–60)
57 (56–60)
Median lower limb MRC score
30 (26–30)
30 (28–30)
Upper motor neuron score
12 (10–13)
0
Data are mean (SD), n (%), or median (IQR). MRC=Medical Research Council. ALSFRS-R=amyotrophic lateral sclerosis functional rating score-revised.
Table 1: Demographic features of patients with amyotrophic lateral sclerosis and neuromuscular disorders mimicking amyotrophic lateral sclerosis
480
Between Jan 1, 2010, and March 1, 2014, we screened 333 patients (206 men and 127 women; mean age 57·6 years [SD 14·6]), 281 (84%) of whom met the inclusion criteria and were therefore enrolled (figure 1). 209 patients were eventually diagnosed with ALS. Of these, we classified 109 (52%) as Awaji definite or probable and 46 (22%) as Awaji possible. 54 (26%) patients did not meet Awaji criteria at initial assessment, although most progressed during followup, leading to reclassification into the Awaji definite or probable group (201 [96%]). Two patients did not progress appreciably and remained Awaji negative, eventually being diagnosed with primary muscular atrophy. 21 (6%) of the 333 patients screened could not undergo TMS testing because of marked hand weakness. We diagnosed 68 patients with non-ALS mimic disorders (table 1, figure 1), who served as pathological controls. Muscle strength, as measured by the Medical Research Council score, was similar between groups. The ALSFRS-R scores indicated a mild level of dysfunction in the ALS cohort. Patients in the non-ALS cohort were younger than patients with ALS. Threshold tracking TMS reliably differentiated ALS from non-ALS disorders (figure 2). Reduction of averaged SICI (interstimulus interval 1–7 ms) seemed to be the most robust variable for differentiation of ALS from non-ALS, with an area under the curve of 0·80 (95% CI 0·75–0·85; figure 3), showing “very good” diagnostic utility. The remainder of the TMS variables had lower diagnostic utility than did averaged SICI, as shown by lower area under the curve, including reduced peak SICI at an interstimulus interval of 3 ms (0·78 [95% CI 0·72–0·84]), reduced cortical silent period duration (0·73 [0·64–0·79]), increased intracortical facilitation (0·62 www.thelancet.com/neurology Vol 14 May 2015
Articles
[0·54–0·68]), increased MEP amplitude (0·56 [0·50–0·65]), reduced resting motor threshold (0·51 [0·50–0·58]), and extended central motor conduction time (0·50 [0·50–0·54). Consequently, we defined a positive index test as either a reduction of averaged SICI (less than 5·5%, as previously reported)19 or inexcitable motor cortex (defined as a resting motor threshold of more than 95% of A 30
ALS Non-ALS
Threshold change (%)
20
10
0
–10
–20
B 30
Threshold change (%)
20
10
0
–10
–20 0
10
20
30
maximum stimulator output).24 With these diagnostic variables, the threshold tracking TMS technique had a sensitivity of 73·21% (95% CI 66·66–79·08) and a specificity of 80·88% (69·53–89·40; table 2). Of the 56 patients with ALS showing a negative index test, defined as short-interval intracortical inhibition of more than 5·5% and absence of motor cortex inexcitability, 25 (45%) were classified as Awaji possible or not meeting criteria (did not initially meet criteria but were later diagnosed with ALS), whereas 31 (55%) were classified as Awaji definite or probable ALS. All patients tolerated the study well; none stopped testing due to intolerance and there were no adverse events. We recorded no adverse events from performance of the index test. Subgroup analysis showed a similar area under the curve between patients with definite or probable ALS (0·79 [95% CI 0·72–0·86]) and those with possible ALS or not meeting criteria (0·83 [0·76–0·89]). Additionally, sensitivity and specificity of threshold tracking TMS was similar between groups (table 2). Mean time between TMS assessment and progression to ALS diagnosis, as defined by the Awaji definite or probable category, was 15·8 months (SD 2·0). An extra 34% of patients with ALS could be diagnosed at initial assessment with use of threshold tracking TMS abnormalities compared with use of the Awaji criteria alone. The sensitivity of the threshold tracking TMS technique was similar between patients with ALS classified as not meeting criteria (72·22% [95% CI 58·35–83·54]) and the Awaji possible group (77·08% [62·68–87·95]; p=0·42). We noted no significant difference in the sensitivity of the threshold tracking TMS technique between patients with signs of UMN dysfunction (UMN score of 3 or more; 74·0% [95% CI 66·28–80·56]) and those without UMN signs (UMN score of less than 3; 65·22% [42·47–83·58];
Insterstimulus interval (ms) 1·0
C 15
10
Sensitivity
Mean SICI, 1–7 ms (%)
0·8
0·6
0·4
Averaged SICI (ISI 1–7 ms) Peak SICI (ISI 3 ms) CSP duration ICF MEP amplitude RMT CMCT
5 0·2
0 ALS
Non-ALS
Figure 2: SICI in patients with ALS and mimic neuromuscular disorders SICI is shown in (A) one patient with ALS and one with a non-ALS mimic disorder (facial-onset sensory motor neuropathy), and (B, C) all patients. ALS=amyotrophic lateral sclerosis. SICI=short-interval intracortical inhibition. Error bars are SEs. p
