Parameters of stimulation electroneuromyography in patients with primary hypothyroidism
Background. The purpose of the work is to identify the parameters of stimulation electroneuromyography (ENMG) in patients with primary hypothyroidism against the background of autoimmune thyroiditis and postoperative hypothyroidism. Materials and methods. The study involved 56 patients with hypothyroidism as a result of autoimmune thyroiditis and 19 patients with postoperative hypothyroidism. The control group consisted of 20 apparently healthy persons. Fifty seven (76 %) patients received substitution therapy using synthetic derivatives of L-thyroxine, and 18 (24 %) patients had subclinical hypothyroidism. Patients were examined using clinical-neurological and electrophysiological methods. The electroneuromyography was carried out on the computerized software complex M-TEST (DX-systems, Kharkiv, Ukraine). Integrated ENMG examination was conducted using standard program package in a specially equipped laboratory. ENMG helped evaluate the parameters of the maximum amplitude of the motor M-response of the limb muscles, the reduction of which is a diagnostic criterion for axon injury, and determine the nerve conduction velocity by the motor fibers of the distal parts of the limb nerves. Reduction of nerve conduction velocity is observed with demyelination of nerve fibers. Results. In case of autoimmune thyroiditis, the sensory nerves of the lower extremities (superficial peroneal and sural ones) were damaged by the mixed type. Signs of axonopathy manifested by a decrease in the action potential amplitude of the superficial peroneal nerve by 32.7 % (p < 0.05) and the sural one by 27.5 % (p < 0.05) compared with the control group, and there was a reduction of nerve conduction velocity of peroneal nerves by 21.9 % (p < 0.05) indicating a damage to the myelin sheath. Patients with postoperative hypothyroidism had mostly signs of axonopathy as evidenced by a decrease in the action potential amplitude of the superficial peroneal nerve by 27.9 % (p < 0.05). While studying the function of the motor fibers of the peripheral nerves (median, peroneal and tibial), we found that the injury to motor fibers was demyelinating in 78.8 % of cases, in the remaining patients (22.2 %) polyneuropathy was mixed (with signs of injury to the myelin sheath and axons). Damage to the ulnar and tibial nerves was obligate, whereas the signs of median nerve injury were observed in 72.8 % of cases. The demyelination of the fast conducting fibers of the peroneal and tibial nerves manifested as prolongation of residual latency by 31.7 % (p < 0.05) and 31.6 %, respectively (p < 0.05), a decrease in nerve conduction velocity during peroneal nerve test by 21.5 % (p < 0.05) and by 19.4 % at the examination of the tibial nerves. 22.2 % of patients with autoimmune thyroiditis had signs of combined myelin lesion and axonal injury, when, in addition to reducing the nerve conduction velocity by the motor fibers of the tibial and peroneal nerves and some prolongation of the residual latency, there was a reliable decrease in the M-response amplitude by 15.6 and 14.8 %, respectively. The patients with postoperative hypothyroidism had the signs of myelinopathy only. Conclusions. ENMG allowed revealing the demyelinating and mixed nature of motor fiber injury and the axonal nature of the peripheral nerve injury, with more pronounced changes observed in autoimmune thyroiditis than in polyneuropathy against the background of postoperative hypothyroidism.
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