Recurrent severe rhabdomyolysis in a pregnancy affected by myotonic dystrophy type 1

Abstract

An 18-year-old female G1P0 at 17+5 weeks pregnant with history of myotonic dystrophy type 1 (DM1) presented with bilateral leg ache, intermittent abdominal pain, and dark urine. Blood tests confirmed severe unprovoked rhabdomyolysis with CK 72546 U/L. CK remained higher than baseline throughout pregnancy and she had two further episodes of severe rhabdomyolysis requiring admission. Nonischaemic forearm exercise testing demonstrated normal response to exercise with no evidence of metabolic myopathy; having normal pre-exercise and post-exercise acylcarnitine profile and amino acid profile, appropriately rising lactate (1.0 mmol/L to 2.4 mmol/L), no significant increase in ammonia (29 μmol/L to 31 μmol/L), and appropriate deoxygenation (PvO2 36 mmHg to 32 mmHg). Three separate urine metabolic screens demonstrated normal glycosaminoglycans (6.0 mg/mmol; 8.6 mg/mmol; 6.3 mg/mmol creatinine; reference range <15.4) and no evidence of fatty acid oxidation defect. A rhabdomyolysis gene test panel involving over 50 genes revealed no underlying cause for rhabdomyolysis. At 33+4 weeks, our patient delivered a stillborn baby strongly affected by DM1 due to anticipation and unable to perform spontaneous respiration. Our patient’s CK fell to 936 U/L one day after birth, lower than all levels during pregnancy, confirming pregnancy as the cause of rhabdomyolysis. We believe this is the first case of spontaneous recurrent severe rhabdomyolysis during pregnancy with DM1.