Nerve Conduction and Heart Rate variability in Patients with Hypothyroidism at a Tertiary Care Centre in Eastern Nepal

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Thyroid hormone effects on many organs including central and peripheral nervous systems. However, these hormones do not affect all systems/organs to a similar extent. Thus, we conducted this study to explore the effect of thyroid hormones on somatic nervous system assessed by Nerve conduction study and cardiac autonomic activity assessed by heart rate variability. The study included newly diagnosed hypothyroid patients and healthy controls. In all subjects NCS were performed in median, ulnar, tibial and sural nerves using Nihonkohden machine Cardiac autonomic control was assessed using Short-term Heart Rate Variability and parameters were analyzed by Time Domain and Frequency Domain methods. Both the groups were comparable in term of age, Body Mass Index, Pulse Rate, Systolic Blood Pressure and Diastolic Blood Pressure. Sensory parameters of NCS showed significant decrease in left median nerve SNAP amplitude (38.24±10.23 Vs 31.59±14.06, P=0.048) and nerve conduction velocity of bilateral median nerve in hypothyroid patients. In motor parameters of NCS, onset latencies of bilateral median nerves and right ulnar nerve were significantly increased in hypothyroid patients. All Time Domain measures of HRV and Frequency Domain measures; LF Power, HF Power and Total Power were significantly decreased (P<0.05) in hypothyroid patients. These HRV parameters are indicators of parasympathetic activity. In newly diagnosed hypothyroid patients, especially median nerve functions (both sensory and motor) and parasympathetic activity were decreased. It reflects that in hypothyroidism both autonomic nervous system and other somatic nerves are not affected in a similar extent.