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 (Abs) are associated with systemic sclerosis (SSc)-myositis overlap syndrome. However, anti-PM-Scl75/100 reactivity detected by line blot (LB) 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 Abs with a speckled pattern. LB testing showed strong anti-PM-Scl75 reactivity, and fingertip ulcers raised suspicion of SSc-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 Abs were not detected by either protein array or immunoprecipitation. The final clinical diagnosis was polymyositis with SSc-spectrum features. We therefore reviewed previously reported cases in which anti-PM-Scl Abs were detected by LB but were not confirmed by other assays. This case demonstrates that myositis with SSc-like clinical manifestations may occur even when anti-PM-Scl75 reactivity is detected only by LB 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 LB should be interpreted with caution when the antinuclear antibody staining pattern is not nucleolar.