Myositis: A Rare First Presentation of Systemic Lupus Erythematosus.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that affects multiple systems with a variety of clinical manifestations and serological abnormalities. Overt myositis is a rare and not well-studied manifestation of SLE, which is associated with a more severe disease course and may be overlooked by clinicians. This case report describes a rare first presentation of SLE with myositis. An 18-year-old female patient presented with a three-month history of generalized muscle weakness, polyarthralgia, and rashes. Physical examination revealed malar rash, a dry scaly pigmented rash affecting the flanks, and a non-blanching purpuric rash with mottled discoloration and a well-defined ulceration, affecting both hands, suggestive of vasculitis. A pigmented atrophic patch on the right upper chest was also suggestive of discoid lupus. Further examination findings included bilateral upper and lower limb weakness affecting proximal muscles (Medical Research Council (MRC) grade 3/5) more than the distal muscles (MRC grade 4/5). The patient's investigation panel revealed leukopenia, anemia, elevated liver enzymes, and elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) as well as significant elevation in creatinine kinase. Further antibody testing revealed positive antinuclear antibodies (ANA), anti-double-stranded DNA (anti-dsDNA), anti-Smith, and anti-U1-ribonucleoprotein (U1RNP), along with electrodiagnostic study supporting the diagnosis of SLE complicated by myositis and vasculitis. Treatment was initiated with prednisolone, hydroxychloroquine, methotrexate, folic acid, and omeprazole with sunscreen. Over the next several months, the patient demonstrated significant clinical and laboratory improvement, regaining full muscle power, with her vasculitis rash also improving and steroid tapering initiated to avoid side effects. This case highlights the importance of recognizing myositis as a rare potential first presentation of SLE and the need for heightened clinical awareness as early diagnosis and treatment is vital for improving long-term outcomes. This case adds to the existing literature and provides a reference for future clinical encounters with such complex cases.