The article is devoted to the clinical case of the development of toxic polyneuropathy in patients receiving thiamazole 25 mg per day in a 43-year-old patient with manifest thyrotoxicosis, which is clinically manifested by severe pain in the muscles of the upper and lower extremities; muscle weakness in the upper limbs. The patient, prescribed by a neurologist, was treated with carbamazepine-retard 400 mg per day for 1 month, and the attending physician decided to replace tiamazole with

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... iouracil 300 mg per day, followed by dose adjustment. The patient categorically refuses surgical treatment or treatment with radioactive iodine. The diagnosis of toxic polyneuropathy was confirmed during the differential diagnosis with inflammatory diseases of the joints and muscles, polyneuropathy on the background of thyrotoxicosis. In the outcome of the treatment, all neurological symptoms were stopped. The observation time on the occasion of polyneuropathy was 1 month, the total time of observation of the patient at the time of publication was 5 years. This clinical case demonstrates the possibility of the development of toxic polyneuropathy in patients receiving thiamazole in the treatment of thyrotoxicosis. Given the low frequency of this complication in clinical practice, it is necessary to draw additional attention of clinicians to this case and recommend including this condition in the differential diagnosis of polyneuropathy.