Here, we report a case of systemic lupus erythematosus in a 13-year-old girl who developed the disease 3 years after thymectomy performed for the treatment of myasthenia gravis. The presenting symptoms were fever, generalized fatigability, bilateral loin pain, weight loss, arthralgia, hair loss, and recurrent painless mouth ulcers. Laboratory findings revealed proteinuria, hematuria, anemia, leucopenia, a high titer of antinuclear antibodies (ANA), anti-dsDNA, and decreased complement (C3 and C4) levels. There was minimal ascitis and pericardial effusion. Renal biopsy showed lupus nephritis class IV. The diagnosis of systemic lupus erythematosus was established based on the clinical and laboratory findings. The activity of systemic lupus erythematosus was controlled by pulsed treatment with methyl prednisolone followed by long-term oral glucocorticoid and immunosuppressive therapy. This study highlights the immune system derangement following thymectomy. It also examines the relevant literature.

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