Endocrine Abstracts

Background: One of the complications of hypothyroidism is the disorder of the neuromuscular system. Myopathic changes often accompany hypothyroidism and are observed in 30-80% of patients. A distinctive feature of hypothyroid myopathies is the reversibility of clinical manifestations and significant improvement of well-being after levothyroxine compensation of the disease. However, the absence of a vivid clinical picture of hypothyroidism, combined with its rare occurrence, complicates early diagnosis and often requires differential diagnosis with other types of myopathies.

Case presentation: Patient T. was complained on progressive pain and muscle weaknessin the lower limbs, impaired coordination. At the time of admission he moved only with support of relatives. From the anamnesis vitae it is known that the patient is the first of 4 children from a close cousin-sister marriage. Primary hypothyroidism was detected at the age of 17, but he did not receive therapy. Physical examination showed pseudohypertrophy of the upper and lower limb girdle muscles, muscle strength was diffusely reduced to 4 points, tone was symmetrically increased, tendon-periosteal reflexes were high, with expansion of reflexogenic zones. Movements in large joints are limited due to muscle contractures. Hormonal blood analysis revealed a significant increase in the level of TSH - more than 500 mIU/l (0.25-3.5), at dilution - 836 mIU/l, of which bioactive TSH - 174 mIU/l; free T4 - 5.15 pmol/l (9-19), free T3 - 2.3 pmol/l (2.6-5.7). Genetic study revealed homozygous mutations in MICU1 gene previously described in myopathy with extrapyramidal symptoms (OMIM: 615673) with autosomal recessive type of inheritance and in IGSF1 gene (NM 001555.5) in exon 8 a variant in hemizygous state leading to amino acid substitution of p.(Lys420Thr), not previously described in the literature. After 2 months from the beginning of therapy with levothyroxine - medically compensated primary hypothyroidism: TSH 1.134 mIU/l (0.4-4.0), T4 free 12.95 pmol/l (7.0-17.6). The patient noted improvement of general well-being, regression of hypothyroidism symptoms, but still had complaints of pain and weakness of lower limb muscles, difficulties with independent movement.

Conclusions: Hypothyroid myopathy usually manifest by nonspecific symptoms in the form of myalgia, muscle cramps, especially increasing with exercise. The severity of myopathy correlates with the duration and degree of thyroid hormone deficiency, which should be taken into account to determine the management of patients with this pathology. An atypical severe course or lack of correction during treatment with levothyroxine should initiate an additional diagnostic search to exclude other forms of myopathy.