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.


Parameters of stimulation electroneuromyography in patients with primary hypothyroidism
For cite: Mìžnarodnij endokrinologìčnij žurnal.2018;14(3): 224-228. doi: 10.22141/2224-0721.14.3.2018.136416Abstract.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.

Introduction
Neurological disorders in patients with pathology of the internal secretion glands are not rare, and problems with the management of such patients often occur [1,2].Significant prevalence of combined neuroendocrine pathology in the structure of general morbidity led to the emergence of a new field of modern medicine -neuroendocrinology, which studies clinical and pathogenetic aspects of neurological complications in endocrine pathology and improvement of treatment methods.Among the pathological states of the nervous system that arise from the imbalance and diseases of the endocrine glands, neurological disorders with hypothyroid conditions of different origin have a special place [3,4].This is due to the severity and the incidence of such disorders.In Ukraine and in other countries, there is a significant increase in the incidence of primary hypothyroidism, which brought it to the fore in the structure of endocrine diseases [5].The increase in the incidence of thyroid pathology is determined by the influence of unfavorable environmental factors, the deterioration of the socio-economic situation in the country, the consequences of the Chornobyl disaster, classifying some regions of Ukraine as those with iodine deficiency.
The most informative method for diagnosing lesions of the peripheral nervous system is electroneuromyography (ENMG) -the recording of electrical potential oscillations in the skeletal muscles, which allows examining objectively the state of damage to the peripheral neuromotor apparatus.For instance, when using this method, the frequency of detecting peripheral nerves lesions increases to 70-90 % [6-10].
The purpose of the study: to identify the parameters of stimulation electroneuromyography 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 (AIT) and 19 patients with postoperative hypothyroidism.The control group consisted of 20 apparently healthy persons.58 (76 %) patients received substitution therapy using synthetic derivatives of L-thyroxin, and 18 (24 %) persons had subclinical hypothyroidism.We used clinical-neurological and electrophysiological methods to examine patients.The electroneuromyography was carried out on the computerized software complex M-TEST (DX-systems, Ukraine).Integrated ENMG examination was conducted on electromyograph with 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 the axon injury, and determine the nerve conduction velocity (NCV) by the motor fibers of the distal parts of the limb nerves.Reduction of NCV is observed with demyelination of nerve fibers.

Results
Using ENMG methods in the diagnostic complex is quite promising for the earliest possible diagnosis of functional changes in the fibers of the peripheral nervous system and for the development of adequate treatment methods that would provide sustainable, long-term results in preventing the damage to peripheral nerves.In this regard, early detection of lesions of the peripheral nervous system in primary hypothyroidism is relevant for the treatment and prevention of their further progression.
It is known that the pathogenesis of polyneuropathy is based on the progressive loss of myelin fibers that is on segmental demyelinization and axonal degeneration, which results in impaired nerve fiber conduction.Due to demyelinization, the myelin sheath, which has a small capacity and high resistance, is injured or lost.Thus, when the potential of demyelinated zone decreases, the current density per unit area of the membrane reduces along with the decrease in resistance.According to the ENMG data, already in case of subclinical hypothyroidism, a part of the patients has dysfunction of peripheral nerves, which is observed in more than 80 % of cases in clinical hypothyroidism.
There are data on the type of nerve fiber lesions in hypothyroidism: some authors adheres to the version of axonopathy (degeneration of the main cylinder with abnormalities of essential element transport from the axon to the plasma, which leads to irreversible degradation of the distal neuronal region) and myelinopathy (focal changes of myelin sheath without damaging the axon with a decrease in the nerve conduction velocity or a mixed type injury).
We have conducted ENMG to study the function of sensory and motor fibers of the limb nerves in order to identify features of ENMG changes in case of primary hypothyroidism.
All patients underwent ENMG of motor (peroneal, tibial, median) and sensory (peroneal, sural) nerves.The following parameters were evaluated while studying the motor nerves: the amplitude (mV) and the duration of the M-response (ms), the area of the M-response to nerve stimulation at the distal and proximal points, the terminal latency (ms), residual latency (m/s), NCV (m/s).While studying the sensor nerves, we checked the action potential amplitude (μV) and NCV (m/s).To evaluate the parameters of the F-wave of the tibial nerves, the minimum latency (m/s), the mean amplitude (μV), the mean NCV and the chronodispersion (ms) were determined.
The analysis of the ENMG parameters of sensory nerves is shown in Table 1.These findings are indicative of the fact that in case of AIT, the sensory nerves of the lower extremities (superficial peroneal and sural ones) were damaged by the mixed type.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 NCV 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 action potential amplitude of the superficial peroneal nerve by 27.9 % (p < 0.05).NCV of the sensory fibers did not differ reliably from that of the control group.

Discussion
Vol.14, No 3, 2018 Mìžnarodnij endokrinologìčnij žurnal, ISSN 2224-0721 (print), ISSN 2307-1427 (online) Оригінальні дослідження /Original Researches/ Thus, in patients with AIT, there was a more significant affection of the sensory nerves of the lower extremities, which combined signs of axonopathy and myelinopathy.In postoperative hypothyroidism, only signs of axonal injury of the superficial peroneal nerve were detected.
While studying the function of 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 (Table 2).
The demyelination of the fast conducting fibers of the peroneal and tibial nerves manifested as prolongation of the residual latency by 31.7 % (p < 0.05) and 31.6 %, respectively (p < 0.05), as a decrease in NCV by 21.5 % (p < 0.05) when testing peroneal nerves and by 19.4 % at the examination of the tibial nerves.
As to the median nerves, there was a slight decrease in the amplitude of the distal M-response, an injury of the myelin sheath was evidenced by a statistically false prolongation of the residual latency and a slight decrease in the NCV.22.2 % of patients with AIT had signs of combined myelin lesion and axonal injury, when, in addition to reduced NCV 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 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 AIT than in polyneuropathy against the background of postoperative hypothyroidism.