[Macrophagic myofasciitis: inflammatory, vaccination-associated muscular disease]

A 67-year-old man presented with a 6-week history of slowly progressive muscle pain and generalized muscular weakness. Neurological examination showed symmetrical proximal weakness (MRC grade 4/5).

Laboratory tests revealed an elevated CK level of 124 U/l (normal < 80). Needle EMG showed pathological spontaneous activity in proximal muscle groups. A diagnostic muscle biopsy taken from the left deltoid muscle revealed a characteristic infiltrate of PAS-positive and acid phosphatase-positive macrophages. Electron microscopic analysis of muscle tissue failed to demonstrate aluminium hydroxide inclusion. Serological analysis excluded antibodies against HAV and HBV but was compatible with a previous tetanus vaccination (antibody titre of 2.3 IE/ml).

A 2-year treatment with steroids and azathioprine led to complete recovery of muscle strength without relapse after discontinuing the immunosuppression.

Macrophagic myofasciitis (MMF) is a rare inflammatory muscle disorder characterized by a characteristic infiltration of muscle tissue by PAS-positive macrophages, which is caused by pathological persistence of vaccine-derived aluminium hydroxide. The diagnosis can only be established by an open muscle biopsy from the muscle that was used for intramuscular vaccination.