Abstract
Background: Deficiency of thyroid hormone has been associated with mononeuropathy, myopathy, sensory neuropathies, and sensorimotor polyneuropathy. Nerve conduction studies (NCSs) are useful to evaluate the electric conduction in motor and sensory nerves and differentiate between axonal neuropathy or demyelination as well as localization of disorder. Hormone replacement therapy (HRT) might restore the nerve function by reversing the biochemical abnormalities.

Aims and Objectives: This study was conducted to observe the effects of hypothyroidism on peripheral nerves by NCS in newly diagnosed patients and effect of short-term (3 months) treatment with hormonal replacement therapy (thyroxine [T4]) on clinical features of peripheral nerve dysfunction and NCS.

Materials and Methods: In this study, 40 patients with newly diagnosed hypothyroidism underwent complete neurological and nerve electrodiagnostic examination. After examination, the patients were provided HRT (T4) for 3 months. Then, neurological and nerve electrodiagnostic examinations were repeated in all the patients.

Results: After 3 months of treatment, free triiodothyronine (FT3) and free T4 (FT4) were increased while thyroid-stimulating hormone was decreased and the results obtained were statistically significant. On diagnosis, carpal tunnel syndrome (CTS) was found in 42.5% of patients and neuropathy in 25% of subjects. After treatment, improvement was seen in 77% of patients with CTS and 70% of patients with neuropathy. Latency of median, tibial, and peroneal motor nerve as well as latency of median and sural sensory nerve were decreased on treatment. Again, amplitude of curve and nerve conduction velocity (NCV) increased in median, tibial, and peroneal nerve on treatment. No significant effects were seen in latency, amplitude of curve, or NCV in ulnar motor and sensory nerve.

Conclusion: The study suggests that abnormalities such as polyneuropathy and entrapment mononeuropathies can be reversed with appropriate treatment in many newly diagnosed hypothyroidism patients.

Key words: Hormone Replacement Therapy; Nerve Conduction Studies; Hypothyroidism; Carpal Tunnel Syndrome; Polyneuropathy