A failure to relax

Mr ST, a caucasian man aged 31 years, presented to hospital with weakness of his arms and legs. He felt unable to cope at home. Six weeks earlier, he sustained burns to his right hand, which occurred while trying to remove the radiator cap from his car. A review of hospital records revealed a history of hypertrophic cardiomyopathy, androgenic alopecia and abdominal pain, for which he had visited the cardiology, dermatology and gastroenterology departments respectively. Examination disclosed a slim male with frontal alopecia and wasted facial and proximal limb muscles. Reflexes were preserved, sensation intact. Notably, hand grip relaxation was delayed (myotonia). Haematological and biochemistry tests were unremarkable. Left ventricular hypertrophy and lateral T wave inversion were present on the electrocardiogram.