Neuromuscular complications of thyrotoxicosis

Abstract

Thyroid hormones exert multiple effects on the neuromuscular system and the brain, with the most important being their role in stimulating the development and differentiation of the neuromuscular system and brain in foetal and neonatal life. In the presence of hyperthyroidism, muscular and neurological symptoms may be the presenting clinical features of the disease. The frequency and severity of neuromuscular complications vary considerably and are probably related to the degree of hyperthyroidism, although in some patients the neuromuscular dysfunction is caused by associated disorders rather than by hyperthyroidism per se. This update focuses on the most common neurological and muscular disorders that occur in patients with thyrotoxicosis. It is beyond the scope of this paper to discuss thyroid eye disease and cardiac complications, in themselves separate complications of specific myocytes.

When to consider thyroid dysfunction in the neurology clinic

“…Thyrotoxicosis can cause weakness and wasting with a predilection for pelvic and shoulder girdle musculature, typically without myalgia 14. It probably only occurs in the context of obvious thyrotoxicosis with significant weight loss (our colleague Dr David Hilton-Jones recalls only one patient in 30 years of muscle specialisation who presented with weakness manifest by inability to perform a 180° turn of her double-decker London bus at Crystal Palace!).…”

Meige's syndrome and hemichorea associated with hyperthyroidism

“…It has been noted that the development of involuntary movement disorders is associated with complex dysfunction within the basal ganglia system [2,3]. Hyperthyroidism is known to affect basal ganglia function through neurotransmitter alteration and/or gene dysregulation, and thyroid hormones could functionally affect the dopaminergic system within the basal ganglia, possibly through an increased sensitivity of the dopaminergic receptors [21][22][23].…”

“…Tremor, muscle weakness, and cognitive dysfunction are common neurologic manifestations of hyperthyroidism [1][2][3]. Movement disorders rarely occur in patients with hyperthyroidism, but have been reported in cases of chorea [4][5][6][7][8], choreoathetosis [9,10], ballism [7], truncal flexion [11], myoclonus [12,13], ataxia [14,15], and stiff-person syndrome [15].…”

Neuropathies in metabolic diseases other than diabetes mellitus

“…Electrophysiological studies reveal a mixed axonal and demyelinating sensorimotor neuropathy. Although rare, this peripheral neuropathy may be an initial clinical feature of hyperthyroidism [13]. Symptoms and signs in such acute cases usually resolve with restoration to a euthyroid state.…”