The effects of hypothyroidism and thyroid replacement on the development of carpal tunnel syndrome.

Hypothyroidism is commonly included as an important risk factor for carpal tunnel syndrome (CTS), yet no study clearly defines the nature of this association. The purpose of this study was to evaluate the relationship between hypothyroidism and CTS in a controlled study. Twenty-six hypothyroid patients (45 hands) meeting our inclusion criteria with a diagnosis of primary hypothyroidism were questioned regarding date of diagnosis of hypothyroidism, duration and dose of thyroid replacement, and the presence, character, and duration of CTS symptoms. Twenty-four healthy volunteers (47 hands) were used as controls. Clinical examination included sensibility testing with Semmes-Weinstein monofilaments, Weber 2-point discrimination testing, examining for thenar muscle atrophy and weakness, Phalen's test, Tinel's sign at the wrist, and the manual compression test. Electrodiagnostic testing including distal motor latency and distal sensory latency was performed on the median nerve at the wrist on all subjects. Nineteen patients (73%; 31 hands [68%]) displayed symptoms of CTS; of these, 16 patients (25 hands) had clinical examinations consistent with CTS. Only 6 of the 16 patients with clinical CTS (7 of 25 hands) had electrical studies that supported a diagnosis of CTS. All these symptomatic patients were biochemically euthyroid. All control subjects had normal electrical study results and normal sensibility testing. Two subjects had positive clinical examinations, giving a false-positive rate of 4%. Carpal tunnel syndrome symptoms are common in hypothyroid patients even when they are euthyroid. In this group of patients, normal median nerve latencies at the wrist in the presence of CTS symptoms and a positive physical examination are more prevalent than expected by the reported sensitivities of electrodiagnostic testing. Standards for assessing normal median nerve latencies may be significantly different in hypothyroid patients.