Both sensorimotor and autonomic neuropathy may be common in hypothyroidism, despite treatment

What is it about?

A new study may provide a previously unknown reason for reduced quality of life in treated hypothyroidism (syndrome T). Systematic investigations of persons with treated hypothyroidism revealed unique signs of sensorimotor dysfunction in quantitative sensory testing (QST). Being marked by thermal and mechanical hypersensitivity, the pattern differs from the constellation seen in diabetes and other conditions leading to polyneuropathy. This may explain some of the sensory symptoms of syndrome T. Additionally, the study found reduced heart rate variability (HRV), depending on the titres of thyroid autoantibodies. This observation, indicating possible autonomic neuropathy, could explain the components of syndrome T that affect the circulatory system. Other results of the study included that both anxiety and depression were significantly more expressed in subjects with autoimmune thyroiditis and that they were also associated with antibody titres. The autonomic function significantly correlated with anxiety and depression, too. Additionally, the depression percentiles in the hospital anxiety and depression scale (HADS) were negatively associated with step-up deiodinase activity (SPINA-GD). In a control group with normal thyroid function, both autonomic and sensorimotor function correlated with the thyroid’s secretory capacity (SPINA-GT).

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Photo by Zohre Nemati on Unsplash

Photo by Zohre Nemati on Unsplash

Why is it important?

About 10% of all patients with treated hypothyroidism report ongoing health issues, including fatigue, impaired memory (“brain fog”), depression, hair loss, palpitations, propensity to fainting, weight gain, both cold and heat intolerance, and fibromyalgia-like musculoskeletal pain. The reasons for this condition, which is referred to as “syndrome T” or “syndrome of residual symptoms of hypothyroidism on T4” (SORSHOT), are unknown. Potential mechanisms include psychological issues, autoimmunity of the thyroid, comorbid autoimmunity affecting other organs, inappropriate dosage of thyroid hormone and wrong modality of treatment (i.e. therapy with levothyroxine only, omitting substitution with liothyronine). However, the evidence is still low, and important questions remain unanswered. The results of the new study may reveal some missing pieces of the jigsaw.

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