J. Clarke Stevens

AAEM minimonograph #26 : The electrodiagnosis of carpal tunnel syndrome

The electrodiagnosis of carpal tunnel syndrome is reviewed, including discussions of old and new techniques of motor and sensory nerve conduction, anomalous innervation, needle electrode examination, and one method of examining a patient with suspected carpal tunnel syndrome. The results of electromyographic testing of 505 patients with carpal tunnel synddrome in Rochester, Minnesota, from 1961 to 1980 are compared with result from previous studies. In the appendixes, a method of performing median motor and sensory nerve conduction studies and Mayo Clinic normal values are provided.The electrodiagnosis of carpal tunnel syndrome (CTS) is reviewed, including discussions of old and new techniques of motor and sensory nerve conduction, anomalous innervation, and needle electrode examination. A variety of sensitive nerve conduction studies (NCSs) are available for the evaluation of a patient with suspected CTS. For any particular patient, the NCS method chosen by the clinical neurophysiologist may vary for a number of reasons, including the severity of the deficit and the presence of superimposed conditions.

Symptoms of 100 patients with electromyographically verified carpal tunnel syndrome

To determine the symptoms of carpal tunnel syndrome (CTS), screening evaluations were performed in 244 consecutive patients with sensory symptoms in the hand and unequivocal slowing of median nerve conduction at the wrist. This yielded 100 patients thought to have no explanation other than CTS for their upper limb complaints. These patients completed a hand symptom diagram (HSD) and questionnaire (HSQ) about their symptoms. CTS symptoms were most commonly reported in median and ulnar digits, followed by median digits only and a glove distribution. Unusual sensory patterns were reported by some patients. Based on the HSQ, paresthesias or pain proximal to the wrist occurred in 36.5% of hands. The usefulness of the HSD and HSQ for diagnosis was determined by asking three physicians, blinded to the diagnosis, to rate the likelihood of CTS in the patients with CTS and in 50 patients with other causes of upper extremity paresthesia. The sensitivities of the instruments ranged from 54.1% to 85.5%. Combining the HSD and HSQ ratings increased the range of sensitivities to 79.3% to 93.7%.

Carpal tunnel syndrome with normal nerve conduction studies

The utility of electrodiagnostic testing in the evaluation of carpal tunnel syndrome (CTS) has been questioned. We studied patients who met the clinical criteria for CTS and compared patients who had normal nerve conduction studies (NCS) with patients who had abnormal NCS. We found that 25% of the CTS patients without confounding neurologic disorders had normal NCS with median palmar nerve stimulation. Patients with abnormal NCS were older and heavier and had more clinical features of CTS. NCS results could not be predicted accurately from clinical features by use of logistic regression models. This was especially true in clinically borderline cases. NCS did not predict the outcome of conservative management. We concluded that NCS provide independent information in the evaluation of suspected CTS, especially when fewer clinical criteria are present, but that NCS are not helpful in predicting the outcome of nonsurgical management. Muscle Nerve 29: 515–522, 2004

The frequency of carpal tunnel syndrome in computer users at a medical facility.

A survey was done of employees who were identified as frequent computer users. Although 29.6% of the employees reported hand paresthesias, only 27 employees (10.5%) met clinical criteria for carpal tunnel syndrome, and in 9 (3.5%) the syndrome was confirmed by nerve conduction studies. Affected and unaffected employees had similar occupations, years using a computer, and time using the computer during the day. The frequency of carpal tunnel syndrome in computer users is similar to that in the general population.

Computed Tomography and Radionuclide Imaging in the Evaluation of Ischemic Stroke

One hundred forty-one patients with cerebral or cerebellar infarction were examined by computed tomography (CT) as soon after the ictus as possible. The examination was repeated in 7 days, and a radionuclide brain scan was performed. The overall detection rate for ischemic infarction was approximately equal for both techniques, ranging from 58% for radionuclide scanning to 66% for the delayed CT. Almost half of the supratentorial infarcts examined by CT on the day of the ictus were demonstrated. Mass effect was observed as early as the first day and as late as the 25th day.

EFFECT OF REFERRAL BIAS ON ASSESSING SURVIVAL IN ALS

We assessed the effect of referral bias on patients with ALS treated at our medical center. A total of 132 subjects were treated by our center over the past 3 years. The referral population had a median survival of 29 months compared to 18 months for the local population (p = 0.007). Referral bias should be addressed when assessing the efficacy of self-selected therapies in the setting of a tertiary ALS clinic.

Neurologic Disorders Masquerading as Carpal Tunnel Syndrome: 12 Cases of Failed Carpal Tunnel Release

We describe 12 patients with a diagnosis of carpal tunnel syndrome in whom carpal tunnel release was unsuccessful and another neurologic disorder was diagnosed subsequently. Final diagnoses included polyneuropathy, radiculopathy, motor neuron disease, spondylotic myelopathy, syringomyelia, and multiple sclerosis. Sources of error by the electromyographer and treating physician were identified. Care must be taken to avoid an inappropriate carpal tunnel operation when clinical or electrodiagnostic features are atypical.

Mitochondrial myopathy and complex III deficiency in a patient with a new stop-codon mutation (G339X) in the cytochrome b gene

A 19-year-old woman complained of life-long exercise intolerance and had chronic lactic acidosis. Neurological examination was normal, but muscle biopsy showed cytochrome c oxidase-positive fibers and marked complex III deficiency. Sequence analysis showed a novel stop-codon mutation (G15761A) in the mitochondrial DNA (mtDNA)-encoded cytochrome b gene, resulting in loss of the last 41 amino acids of the protein. By PCR/restriction fragment-length polymorphism (RFLP) analysis, the G15761A mutation was very abundant (73%) in the patients muscle, barely detectable (less than 1%) in her urine, and absent in her blood; it was also absent in muscle, urine and blood from the patients mother. This mutation fulfills all accepted criteria for pathogenicity.

Incidence of aspiration pneumonia in ALS in Olmsted County, MN

Aspiration pneumonia is believed to be an uncommon complication of amyotrophic lateral sclerosis (ALS). However, the incidence of aspiration pneumonia and its contribution to morbidity and mortality are unknown in ALS. All cases of ALS from Olmsted County, Minnesota from 1990 to 2005 were reviewed. Baseline demographics were noted for all cases. Dates of diagnosis, PEG tube placement, death and survival status were also noted. All cases of aspiration pneumonia were identified. Forty cases of ALS were identified over the 15‐year period. The incidence rate was 1.7 cases per 100,000 person years. There was an overall mean survival of 26 months from diagnosis. Aspiration pneumonia occurred in five (13%) cases. There was a mean survival of two months following aspiration pneumonia. The strongest risk factor for aspiration pneumonia was nursing home residence with a relative risk of 7.1 (p = 0.02) We conclude that the incidence rates and demographics of our ALS population have remained stable over time. Aspiration pneumonia occurs in a minority but is associated with a high mortality. ALS subjects residing in nursing homes are at the greatest risk.

Motor unit number estimates in idiopathic Parkinson's disease.

We previously reported changes in motor unit morphology in patients with Parkinsons disease (PD) using subjective and computerized quantitative electromyography. Now, we present data on motor unit number estimates (MUNE) to address the hypothesis of motor neuron dropout in PD. Twenty patients with PD and 20 age-matched control subjects were screened by clinical criteria and nerve conduction studies to exclude those with neuropathy. Motor unit number estimates in the extensor digitorum brevis and hypothenar group were assessed by three different MUNE techniques. The MUNE technique types included (1) the statistical method developed by Daube, (2) a threshold method, and (3) an F-wave method. The overall multivariate comparison for the six MUNE measurements was significantly lower for the patients than the controls (P=0.02). The only significant difference in the individual measures was found in the threshold MUNE method of the hypothenar group (P<0.05). These results are consistent with those of our previous work, and both support the hypothesis that mild motor neuron dropout occurs in idiopathic PD. However, MUNE methods characteristically have large standard deviations which make it difficult to detect small changes. Progress in decreasing the variance of MUNEs will facilitate their use in detecting small motor unit number changes in neurodegenerative disease.