Weak at the knees

• Published in: Practical neurology Vol. 22; no. 3; pp. 253 - 255
• Main Authors: Kramarz, Caroline, Hayat, Tayyib, Gran, Bruno
• Format: Journal Article
• Language: English
• Published: England BMJ Publishing Group Ltd 01.06.2022; BMJ Publishing Group LTD
• Subjects: Antibodies; Blood pressure; Electrolytes; Guillain-Barre syndrome; Hypokalemia; Illnesses; Intensive care; Musculoskeletal system; myopathy; neuromuscular; Ostomy; Paralysis; Potassium; Rhabdomyolysis; Spinal cord; Test yourself; Thyroid gland; Tracheotomy; West Nile virus; myopathy; neuromuscular
• ISSN: 1474-7758; 1474-7766
• DOI: 10.1136/practneurol-2021-003190

Correspondence to Dr Caroline Kramarz, Neurology, Queen's Medical Centre Nottingham University Hospital NHS Trust, Nottingham NG7 2UH, UK; caroline.kramarz@nhs.net Clinical case A 24-year-old man of Nigerian heritage presented to the emergency department with a 1-day history of acute, ascending limb weakness. A clinical geneticist advised that genetic testing was unnecessary in view of the abnormal thyroid function, which was consistent with thyrotoxic periodic paralysis. The initial presentation may involve a progressive motor paralysis (box 1 gives further differentials).Box 1 Differential diagnosis of acute motor paralysis Acute inflammatory demyelinating polyneuropathy (Guillain-Barré syndrome) Infections, for example, Lyme disease, West Nile virus, Japanese encephalitis virus Toxins and drugs, for example, botulism, organophosphate poisoning, neuromuscular blocking agents, diuretics, laxatives Electrolyte derangement and skeletal muscle channelopathies including the periodic paralyses and non-dystrophic myotonia, for example, paramyotonia congenita Myasthenia gravis Myopathies and myositis Vasculitis Spinal cord injury including spinal shock The normal blood gas bicarbonate concentration helped us to diagnose the cause of hypokalaemia. Rhabdomyolysis would be in keeping with the acute nature of the presentation but the absence of myoglobinuria, persistently normal renal function and rapid normalisation of the serum creatine kinase concentration within 2 days after being checked serially (1744, 326 and 41 U/L (24–195)) makes this a less likely cause of prolonged weakness.