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A 25 year old male shopkeeper was brought to the emergency room with sudden onset flaccid quadriparesis of five hours' duration. The proximal muscle groups were weaker than the distal. He gave a history of similar episodes for the last four years. The episodes usually followed a period of rest after moderate to severe exertion. Each attack lasted three to 10 hours, and was followed by spontaneous complete recovery. The frequency varied from once per day to three times per week. There was no history of loss of consciousness, diplopia, drop attacks, dysarthria, dysphagia, alcohol, or drug intake. There was no history suggestive of hyperthyroidism. His parents and two sisters denied any history of similar neurological illness or hyperthyroidism. Clinically he had flaccid motor paralysis with absent deep tendon jerks. There was mild wasting of the thigh and arm muscles. Cranial nerves, fundi, higher mental functions, and sensations were normal. There was no goitre, tachycardia, tremor, or weight loss. Abnormal investigations at admission are listed in box 1.
Box 1: Investigation results (normal range)
Potassium: 2.1 mmol/l (3.5–5.5)
Free thyroxine 43 pmol/l (9–24), triiodothyronine 3.5 nmol/l (1.2–3.1), and thyroid stimulating hormone <0.01 mU/l (0.2–5 mU/l)
Electrocardiography: normal sinus rhythm, flattened ST segment, presence of U waves, and prolonged QU interval
Serum creatine kinase: 1190 U/l (10–190)
Electromyogram: myopathic pattern
Muscle biopsy: vacuolar myopathy
Blood counts, creatinine, serum sodium, chloride, bicarbonate, calcium, glucose, cortisol, and supine aldosterone concentrations were normal. Nerve conduction velocities were normal.
- What is the diagnosis?
- What is the basic pathophysiology of this disorder?
- How will you prevent further attacks?
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