Dermatomyositis masking late onset Pompe disease in a patient with proximal muscle weakness

Slowly progressive proximal muscle weakness in an otherwise healthy male posed particular challenges for the treating physicians, considering the wide range of possible differentials. Here we present a case of a 52-year-old male with paraparesis, elevated creatine kinase-levels, antibodies against the Mi-2 antigen and subtle skin lesions, leading to subsequent treatment for dermatomyositis. Beyond that, exome sequencing revealed biallelic variants in the gene encoding acid alpha-glucosidase with concordant reduced enzymatic activity in fibroblasts, indicating late onset Pompe disease. Subsequently performed magnetic resonance imaging revealed a pattern of involvement typical for LOPD, but histological workup from the vastus lateralis muscle was more indicative of an immune-mediated myopathy. After treatment for dermatomyositis and Pompe disease the patient showed an improvement in skin changes and a halt in muscular weakness. In conclusion, both entities could be seen in the patient. However, early and prolonged subclinical hyper-CK-emia hinted at Pompe disease as the primary entity.