Unusual presentation of PYGM gene mutation as late-onset McArdle disease with camptocormia: a case report.

Background: Glycogen storage disease type 5 (McArdle disease) leads to a deficiency in the activity of myophosphorylase resulting in an impaired glucose utilization. The disease can be caused by a variety of mutations in the PYGM gene, and its typical clinical manifestation is muscles weakness within the first three decades of life.

Case presentation: In this case report we present the diagnostic work-up of a physically active 78-year-old Caucasian patient suffering from a 2-year history of progressive camptocormia including clinical, radiologic, histological, and genetic tests. There was no history of neuro-muscular diseases in the family. Serum CK levels were moderately increased while other blood/urine parameters were normal. Magnetic resonance imaging showed fatty remodeling of the muscles of the back. Histochemical examination of a muscle biopsy revealed the absence of myophosphorylase activity, while gene analysis identified a known early-onset McArdle mutation in the PYGM gene.

Conclusion: This case highlights that the clinical spectrum of PYGM gene mutation typically manifest during adolescence, but it is also a differential diagnosis in late onset muscle disorders and emphases the investigation of the role of ACE inhibitors in this disease.