Clinico-sero-pathological Characteristics of Anti-Ha Antisynthetase Syndrome.

To define the clinical, serological, and muscle histopathological characteristics, as well as treatment outcomes, of patients with anti-Ha antibody. We performed a retrospective analysis of clinical, serological, and pathological data and long-term treatment outcomes of anti-Ha patients between January 2005 and July 2023 at our center. Anti-Ha antibody was identified by immunoblot and reconfirmed by immunoprecipitation. Of the 570 patients with idiopathic inflammatory myopathies, 17 (3.0%) were found to be anti-Ha positive, of whom 5 (29.4%) were also positive for another myositis-specific antibody (MSA). All patients with anti-Ha antibody as the single MSA (12/17, 70.6%) had clinical and histopathological evidence of muscle damage. Skin lesions were identified in nine of them (75%), while both interstitial lung disease and Raynaud's phenomenon were only seen in four patients. A necrotizing myopathy without a perifascicular pattern was the most common pathological manifestation (50%). Perifascicular necrosis (PFN) and myofiber major histocompatibility complex class-II expression were observed only in one and four patients, respectively. Muscle weakness relapse was reported in five patients, and skin rashes worsening were observed in one patient. Most of the anti-Ha patients (66.7%) finally achieved a favorable outcome at last follow-up. Anti-Ha antibody might not be as rare as previously thought and may coexist with other MSAs. Muscle damage is the most common manifestation in anti-Ha patients, while extra-muscular symptoms except for the cutaneous manifestations are unusual. The histopathological features varied with a predominance of necrotizing myopathy without PFN. These patients often finally had favorable outcomes, although relapses often occur.