Retiform purpura and blue toe: an unusual presentation of systemic lupus erythematosus.

Retiform purpura (RP) is a morphological pattern of cutaneous ischemia resulting from vascular compromise. Its clinical relevance lies in its orientation toward vasculitis or thrombotic vasculopathy. We report the case of a woman with painful violaceous retiform lesions on the distal lower extremities, Raynaud's phenomenon with a "blue toe" on the hand, and polyarthralgias. Laboratory workup revealed antinuclear antibodies (ANA) 1:2560 (AC-5 pattern), anti-RNP > 240 U/mL, anti-Sm > 320 U/mL, low C4, and negative antineutrophil antibodies (ANCA) and rheumatoid factor. Magnetic resonance imaging showed diffuse muscular edema and bilateral fascial thickening; computed tomography reported reactive adenopathies. Skin biopsy demonstrated ischemic changes consistent with small vessel involvement in a mixed vasculitic/vasculopathic pattern, with epidermal necrosis and intraluminal fibrin. Systemic lupus erythematosus (SLE) with features of small vessel vasculitis was diagnosed. Treatment included methylprednisolone and prednisone pulses, cyclophosphamide, rituximab, and alprostadil for digital ischemia, with clinical improvement. RP may reflect a mixed inflammatory/thrombotic process in the context of overlapping autoimmunity. Deep biopsy, autoimmune profiling, and assessment of prothrombotic state are key axes for decisions regarding immunosuppression and/or antithrombotic strategies. Key Points • Retiform purpura is a high-risk cutaneous pattern that requires early differentiation between vasculitis and thrombotic vasculopathy, as each condition demands divergent therapeutic strategies (immunosuppression versus antithrombotic therapy). • In patients with SLE, cutaneous vasculitis - though uncommon - may present with a dominant ischemic phenotype (retiform purpura, digital ischemia) that initially mimics medium-vessel vasculitis such as polyarteritis nodosa or systemic sclerosis; accurate diagnosis requires integration of clinical, histological, and immunological data. • Management of severe ischemic SLE with a mixed inflammatory/occlusive mechanism may require a parallel approach: intensive immunosuppression to control vascular inflammation, combined with vasoactive and anticoagulant measures to preserve distal perfusion and tissue viability.