A 49-year-old man with contractures, weakness, and cardiac arrhythmia

The patient first noticed elbow contractures in childhood, and had always had small biceps muscles. He was never able to run as fast as his peers, and described a sensation of muscle tightening if he tried to run or move quickly, but was unaware of other weakness or functional limitation. At age 44 years, during preoperative assessment for an inguinal hernia repair, he was found to be in asymptomatic atrial flutter and was placed on warfarin. He underwent successful cardioversion, but was again in atrial flutter 2 months later. He was referred to Mayo Clinic, where atrial fibrillation with right bundle branch block and left anterior fascicular block was diagnosed. Transesophageal echocardiogram at that time was normal apart from a patent foramen ovale with bidirectional shunting. He was cardioverted successfully to normal sinus rhythm with first-degree atrioventricular block, right bundle branch block, and left anterior fascicular block. Five years later, routine serologic evaluation revealed mildly elevated aspartate aminotransferase (AST) and alanine aminotransferase (ALT), which remained elevated for 1 year, suspected to be related to his liver, so he returned to Mayo Clinic for gastroenterologic evaluation. During this evaluation, serum creatine kinase (CK) was found to be elevated at 1,146 U/L (normal 52–336 U/L), which prompted neurologic referral. The patient was an active hog farmer. He routinely rode a stationary exercise bike for 35 minutes each night at a rate of 30–32 miles per hour without difficulty. He had recently noticed problems carrying heavy bales or feed sacks, and had difficulty lifting up to 50 pounds past the level of his chest. He developed tightness in his leg muscles if he carried 30–40 pounds up stairs. He denied muscle pain, new muscle atrophy, or episodes of dark urine. He had no difficulty squatting or rising from chairs, speaking, chewing, or swallowing …