Giant cell arteritis with myeloperoxidase anti-neutrophil cytoplasmic antibody seropositivity in a patient with systemic sclerosis.

To the best of our knowledge, systemic sclerosis with overlapping characteristics of both microscopic polyangiitis and giant cell arteritis (i.e. microscopic polyangiitis involving the superficial temporal artery or giant cell arteritis with myeloperoxidase anti-neutrophil cytoplasmic antibody seropositivity) has not been reported previously. An 82-year-old woman with diffuse cutaneous systemic sclerosis experienced dyspnoea on exertion and fever. No signs of infection were observed on computed tomography. Her fever persisted despite antibiotic treatment for occult bacterial infection and secondary Clostridioides difficile-associated diarrhoea. Microscopic polyangiitis was suspected because of myeloperoxidase anti-neutrophil cytoplasmic antibody seropositivity, and giant cell arteritis was suspected as a differential diagnosis due to swelling of the superficial temporal artery. Arterial biopsy revealed inflammatory cell infiltration with granuloma formation. Based on the presence of granulomatous inflammation in the superficial temporal artery, we concluded that giant cell arteritis with myeloperoxidase anti-neutrophil cytoplasmic antibody seropositivity occurred as a complication. After glucocorticoid therapy, her fever and dyspnoea on exertion improved with a gradual decline in the serum myeloperoxidase anti-neutrophil cytoplasmic antibody levels. It is possible that vasculitis occurs as a complication in patients with systemic sclerosis in cases where the fever persists and cannot be explained by systemic sclerosis itself, infectious disease, or malignancy. Clinicians must be careful not to prematurely diagnose microscopic polyangiitis based on myeloperoxidase anti-neutrophil cytoplasmic antibody seropositivity or giant cell arteritis based on the swelling of the superficial temporal artery. Careful evaluation of the presence of granulomatous inflammation in an arterial biopsy specimen is essential to differentiate between microscopic polyangiitis and giant cell arteritis.