ABSTRACT
Macrophagic myofasciitis (MMF) is a rare disease, often associated with the pathological persistence of aluminum hydroxide used in some vaccines, and is characterized by macrophage infiltration of the muscle. We report a case of MMF, initially thought to be a metastatic infection. A 38-year-old woman presented with fever, as well as pain and weakness in both thighs. On physical examination both thighs were swollen and lower-extremity motor-power was decreased to grade III. Laboratory tests showed leukocytosis and elevation of acute phase reactants, but all muscle enzymes except lactate dehydrogenase (LDH) were within normal range. Initially metastatic infection was suspected but she was diagnosed with MMF by muscle biopsy showing heavy CD68 positive macrophage infiltration. Her myalgia and muscle weakness improved after systemic steroid treatment. This case suggests that MMF might be considered for a patient with unexplained inflammatory myopathy with or without a history of vaccination.