Full Recovery Over One Year of the Overlap Syndrome Scleromyositis to Maintenance Therapy with Mycophenolate Mofetil and Rituximab, which Relapsed within 8 Months of Discontinuation.

Scleromyositis (SM) is an emerging, distinct entity within the spectrum of diffuse systemic sclerosis (SSc) and autoimmune inflammatory myopathies. It can carry a poorer prognosis due to multisystem involvement and extramuscular complications, with no consensus on treatment strategies currently available. We report on a 20-year-old woman with a history of recurrent infections over the past year, who presented with persistent myalgias for four months. On examination, she exhibited muscle weakness in the scapular and pelvic girdles, along with sclerodactyly. Laboratory results showed elevated creatine kinase (13,000 U/l), aldolase (15.6 U/l), lactate dehydrogenase (1,481 U/l) and myoglobin (4,400 ng/ml). Autoimmune screening was positive for antinuclear antibodies, anti-PM-scleroderma (anti-PM-Scl) 75 and 100, and anti-CENP-B antibodies. An MRI of the pelvic girdle indicated acute/subacute myositis, and electromyography revealed both distal and proximal myopathy. Muscle biopsy showed extensive necrosis with minimal inflammatory infiltration. Nailfold capillaroscopy demonstrated an early scleroderma pattern, while CT and spirometry revealed mild interstitial restrictive lung disease. Initial treatment involved intravenous immunoglobulin (IVIG), mycophenolate mofetil (MMF) and prednisolone. This was followed by maintenance therapy with MMF and rituximab (RTX) every six months for the first year. Over six months, the patient showed progressive improvement in muscle strength and normalisation of muscle enzyme levels. In conclusion, SM presents with variable phenotypes, ranging from mild to extensive systemic involvement. This case underscores the importance of individualised patient stratification and highlights the need for structured induction and maintenance therapy due to the disease's extensive activity. LEARNING POINTS: Scleromyositis (SM) is a rare and poorly understood condition that combines features of systemic sclerosis and immune-mediated myositis, often linked to anti-PM-scleroderma antibodies.Despite efforts to classify SM, it demonstrates unique clinical patterns that distinguish it from other myositis subtypes.The management of SM remains challenging, as there are no established guidelines or standardised treatment protocols.