Polymyositis with Scleroderma-like Features and an Anti–PM-Scl75 Antibody Detected by Line Blot but Not by Protein Array or Immunoprecipitation: A Case Report and Literature Review

Anti-PM-Scl antibodies are associated with systemic sclerosis-myositis overlap syndrome. However, anti-PM-Scl75/100 reactivity detected by line blot assays is frequently not confirmed by protein array or immunoprecipitation, indicating that such results should be interpreted with caution in Japan. A 72-year-old woman developed limb fatigue and Raynaud's phenomenon, followed by muscle weakness, elevated serum creatine kinase levels, and gangrenous changes in several fingers. Magnetic resonance imaging and muscle biopsy findings were consistent with myositis. She tested positive for antinuclear antibodies with a speckled pattern. Line blot testing showed strong anti-PM-Scl75 reactivity, and fingertip ulcers raised suspicion of systemic sclerosis-spectrum manifestations. Treatment with prednisolone (25 mg/day) and high-dose intravenous immunoglobulin improved the muscle enzyme elevation and digital lesions. However, anti-PM-Scl75 antibodies were not detected by either protein array or immunoprecipitation. The final clinical diagnosis was polymyositis with systemic sclerosis-spectrum features. We therefore reviewed previously reported cases in which anti-PM-Scl antibodies were detected by line blot but were not confirmed by other assays. This case demonstrates that myositis with systemic sclerosis-like clinical manifestations may occur even when anti-PM-Scl75 reactivity is detected only by line blot assay. Although autoantibody testing may aid in the diagnosis of myositis, the results should be interpreted in light of the analytical characteristics of each assay. In particular, anti-PM-Scl75/100 reactivity detected by line blot should be interpreted with caution when the antinuclear antibody staining pattern is not nucleolar.