Childhood-Onset Anti-Ku Antibody-Positive Generalized Morphea with Polymyositis: A Japanese Case Study.

We report a 16-year-old Japanese girl with anti-Ku antibody-positive generalized morphea and polymyositis who, at the age of 7 years, developed multiple brownish plaques on her left forearm that gradually extended to her upper arm, back, and left thigh, which a skin biopsy revealed as morphea. Laboratory testing was positive for antinuclear antibody and a high serum creatine kinase level. Although there were no clinical signs of muscular involvement, magnetic resonance imaging revealed findings consistent with myositis. The patient is one of the youngest reported cases positive for anti-Ku antibody. Anti-Ku positivity concomitant with generalized morphea is rare.