[Sequential autoimmunity? The rare case of MDA5 dermatomyositis and sarcoidosis].

Background: Anti-MDA5 positive dermatomyositis is a rare subtype of idiopathic inflammatory myopathies often accompanied by rapidly progressive interstitial lung disease and severe cutaneous ulcerations. It is associated with a high mortality. The simultaneous occurrence of sarcoidosis with multisystemic involvement of myositis has only been described very rarely in the literature to date.

Case report: We report the case of a 39-year-old man with a 3-year history of anti-MDA‑5 positive dermatomyositis who developed a worsening of dyspnea and hypercalcemia with acute kidney injury and a marked deterioration in his general condition after successive reductions in immunosuppressive therapy. A bronchoscopy and lymph node biopsy ultimately confirmed the diagnosis of sarcoidosis.

Conclusion: This case report illustrates the importance of continuously re-evaluating the diagnosis when new symptoms occur during the course of a rare disease. In the presence of pronounced lymphadenopathy, new hypercalcemia and lung parenchymal changes atypical for dermatomyositis, the differential diagnosis of sarcoidosis should also be considered.