The filters were set at 2 Hz–10 kHz for the motor studies and 5 Hz–2 kHz for the sensory studies. The present study was conducted to assess the electrophysiological alterations in peripheral and CNS in newly diagnosed hypothyroid patients. It becomes important to know the abnormalities in VEP if electrodiagnostic techniques are to be used in the early detection of nerve involvement in hypothyroidism. It is a noninvasive and simple electrophysiological test to assess the effects of hypothyroidism on the central nervous system (CNS). VEPs are potential differences recorded from the scalp by electrodes in response to visual stimuli. Hypothyroidism has been reported to be associated with prolonged latency and decreased the amplitude of visual evoked potentials (VEPs). Some studies have reported prolongation of both central and peripheral conduction time even in subclinical hypothyroid conditions.
Brainstem auditory evoked potential (BAEP) is a method used to assess the functional integrity of the thalamocortical projections relaying to the primary auditory cortex and association cortex. About 37% of the patients of the patients with hypothyroidism were found to be suffering from hearing loss. Manifestations of cranial nerve involvement in thyroid dysfunction include sensory neural hearing loss and ophthalmopathy. Carpal tunnel syndrome is the main cause of peripheral nerve damage in hypothyroidism due to median nerve entrapment. The most commonly involved nerves are the sural and median nerves, as the distal and sensory nerves are affected earlier. The peripheral polyneuropathy may be due to the defect in nerve cell body, axons or myelin sheath and it results in decreased nerve conduction velocities and amplitudes in peripheral nerves. In many studies conducted in the past, polyneuropathy was observed to be associated with hypothyroidism. Patients develop the usual manifestations of peripheral neuropathy as loss of reflexes, proximal muscle weakness, numbness, paresthesia, decreased sensations, and slowed muscle contraction and relaxation with prolonged. Usually, hypothyroidism has both central and peripheral nerve involvement. The prevalence of neuromuscular dysfunctions in thyroid disorders was found to be 20%–80%. Some of the usual signs of hypothyroidism are muscle weakness, fatigue, muscular and mental sluggishness, weight gain, constipation and intolerance to cold. As a result, hypothyroidism may cause various neurological signs and symptoms.
Both these hormones exert a number of effects on the neuromuscular system and brain. The thyroid gland secretes triiodothyronine (T3) and thyroxine (T4) hormones which play an important role in tissue development and metabolism.
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