Case Presentation: A 35-year-old Caucasian male patient presented to our clinic complaining of fatigue, proximal muscle weakness, and pain. Twelve years ago, he was diagnosed with acute myeloid leukaemia, and due to poor prognostic factors, he underwent allogeneic HSCT from his sister, an HLA full-matched sibling donor. His past medical history is significant for chronic skin GVHD findings and avascular necrosis of the femur head due to steroid usage. Initial vital signs were within normal limits. Physical examination detected abduction limitations at the left shoulder and left hip due to old aseptic necrosis. Motor strength was 3/5 in both upper and lower proximal muscles. The sensation was intact. The rest of the physical examination was within normal limits. Laboratory tests revealed hypercalcemia with a calcium level of 13 mg/dL, elevated creatine phosphokinase (CPK) level of 2826 u/L, erythrocyte sedimentation rate (ESR) of 30 mm/hr. Further test results showed parathormone (PTH) and 1,25 (OH)2 vitamin D levels were suppressed. 18F-FDG PET scan ruled out secondary malignancy and showed extensive generalized proximal muscle involvement. The patient refused to undergo a muscle biopsy, but an electromyogram (EMG) confirmed a polymyositis pattern. The patient was diagnosed with polymyositis as a component of chronic GVHD. Treatment with cyclosporine and steroid resulted in complete remission. He is still under immunosuppressive therapy on routine follow-up.

Discussion: Graft versus host disease (GVHD) is an immune-mediated disease resulting from a complex interaction between donor and recipient adaptive immunity. Chronic GVHD describes more diverse syndrome developing after day 100 of allogeneic hematopoietic stem cell transplantation (HSCT). It occurs in up to 60% of patients with allogeneic HSCT and is frequently seen in patients with older age and a history of acute GVHD. Ocular, oral, gastrointestinal, pulmonary, and neuromuscular manifestations are mostly seen. Musculoskeletal manifestations of chronic GVHD are infrequent, and when present, do not usually manifest as polymyositis. Polymyositis typically presents as diffuse, generalized myopathy with preserved sensation and elevated CPK and aldolase. Although chronic GVHD induced polymyositis is rare and there is no well-established treatment experience, several studies reported to respond to corticosteroids alone or in combination with cyclosporine.

Conclusions: It is important for clinicians to be familiar with this polymyositis phenomenon as a manifestation of chronic GVHD, especially since myopathy etiology in these patients may easily be mistaken.