We describe a patient with primary hypothyroidism due to autoimmune thyroiditis, presenting with acute myoedema and spontaneous rhabdomyolysis. During his hospital stay, he developed altered sensorium due to hypo-osmolal hyponatraemia and later developed bilateral foot drop that responded to appropriate treatment.
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Muscle weakness, aches and cramps, stiffness and delayed tendon jerk relaxation are usual features of hypothyroid myopathy (30–80%), while muscle hypertrophy, myoedema and wasting are occasionally seen.1 2 They evolve gradually over a long period of time. We report a patient with primary hypothyroidism, who presented with acute generalised myoedema, stiffness and spontaneous rhabdomyolysis.
A 41-year-old man presented with generalised body swelling and increasing stiffness for 2 weeks. He had experienced severe aches and pains, lower limb weakness and oliguria, for 3 days prior to his admission. He denied any form of strenuous muscle exercise. He had been a diagnosed hypertensive for 8 years with poor drug compliance. He was diagnosed to have autoimmune thyroiditis with primary hypothyroidism 6 years ago, requiring thyroxine for 6 months only. He remained euthyroid (serum thyroid-stimulating hormone (TSH) 2.5 μIU/ml) thereafter until about a month prior to admission.
On examination, he was pale, afebrile but tachypnoeic, had peri-orbital puffiness and no goitre. His pulse was 78 beats/min regular, blood pressure 170/110 mmHg and voice was hoarse. All his limb muscles were swollen, firm, nonpitting, severely stiff and hypertonic but distinctly nontender, characteristically described as myoedema. He had proximal muscle weakness in both shoulder (4/5) and pelvic girdles (3/5) and had pseudomyotonia. Relaxation of deep tendon reflexes was grossly delayed. He had a few coarse crepitations in the left infrascapular region. Other systemic examinations were normal.
Investigations revealed: haemoglobin 10.7 g/dl, total leucocyte count 10 × 109/l with 90% polymorphs, serum Na+125 mEq/l, K+ 3.6 mEq/l, urea 14.2 mmol/l, creatinine 133 μmol/l, random blood glucose 6 mmol/l , serum aspartate transaminase 19 IU/l, alanine transaminase 77 IU/l, creatine kinase-MM (CK-MM) 80 730 IU/l (normal up to 20 IU/l) and aldolase 35 IU/l (1–7.6 at 37° C) and serum myoglobin > 85 ng/ml. The centrifuged plasma was normal in colour. Arterial blood gas analysis showed PaO2 83, PaCO2 30, pH 7.5, HCO3 23.9. His serum T3 was 0.2 ng/ml (0.6–1.2), T4 9 ng/ml (60–130), TSH 58.9 μIU/ml (0.3–5), cortisol at 08.00 h 500 nmol/l (400–600) and at 16.00 420 nmol/l (200–400). Antimicrosomal antibody titre was abnormally elevated. Electromyogram (EMG) revealed polyphasic action potentials consistent with myopathy.
He received intravenous dextrose-saline, rapidly increasing doses of L-thyroxine from a starting dose of 25 μg to 150 μg in one week, cefotaxime and amikacin. On day 3 of admission, he became drowsy and disoriented, when his serum Na+ was 110 mEq/l, serum osmolality 232 mOsmol/kg and urine osmolality 345 mOsmol/kg, indicating hypo-osmolal hyponatraemia. In addition to intravenous saline, he received oral salt supplementation and intravenous hydrocortisone. His sensorium gradually improved over the following 10–12 h with an increase in serum Na+ to 124 mEq/l and serum osmolality to 258 mOsmol/kg. Urine spot Na+ dropped from 61 mEq/l to 30 mEq/l. On day 5, he developed bilateral foot drop with sensory loss in L4–5/S1 dermatomes. Nerve conduction velocity showed impaired conduction through the common peroneal nerve. After 3 months of thyroxine replacement, his muscle rigidity and stiffness were markedly reduced and power in foot dorsiflexors improved to 3/5. At 6 months of follow-up serum CK-MM had decreased to 432 IU/l and serum myoglobin was undetectable.
The clinical spectrum of hypothyroid myopathy is varied. Delayed relaxation of tendon jerks and proximal muscle weakness correlate with biochemical severity of hypothyroidism (serum T4 <20 ng/ml).3 Acute myoedema and rhabdomyolysis are, however, distinctly rare.2 4 Raised serum CK-MM and myoglobin, typical myopathic EMG, low T4 and high TSH, and their reversibility with L-thyroxine treatment supported the diagnosis of hypothyroid myopathy with rhabdomyolysis.
Transient hypothyroidism many years earlier followed by complete clinical and biochemical recovery suggested autoimmune thyroiditis, which eventually led to atrophy of the thyroid and hypothyroidism. The muscle involvement in hypothyroidism is caused by changes in muscle fibres from fast twitching type II to slow twitching type I fibres, deposition of glycosaminoglycans, poor contractility of actin–myosin units, low myosin ATPase activity and low ATP turnover in skeletal muscle.5
Hypo-osmolal hyponatraemia is occasionally encountered in primary hypothyroidism. It is accompanied by a decrease in glomerular filtration rate, inappropriately elevated circulating antidiuretic hormone, because of its slow catabolism, and concomitant cortisol deficiency.6 Bilateral symmetrical foot drop in this patient was possibly caused by peroneal neuropathy due to decubitus pressure or glycosaminoglycans deposition in the perineural sheath.7
myoedema, muscle hypertrophy, and wasting are uncommon features of hypothyroid myopathy
CK-MM can be used as a marker of hypothyroid myopathy
hypothyroid myopathy responds to L-thyroxine therapy
hypo-osmolal hyponatraemia can be an important cause of altered sensorium in long-standing untreated hypothyroidism