Primary Cutaneous Diffuse Large B-Cell Lymphoma With Initial Atypical Clinical Presentation as Annular and Arcuate Plaques, Histologically Mimicking Interstitial Granulomatous Dermatitis

Primary cutaneous B-cell lymphoma most commonly presents as solitary or multiple violaceous papules, nodules, or plaques depending on the specific subtype. It tends to have an aggressive clinical course. Secondary cutaneous involvement of systemic or nodal lymphoma also needs to be excluded. We describe a unique case of a 73-year-old man with presentation as striking annular and arcuate lesions clinically and histologically mimicking an interstitial granulomatous dermatitis, such as granuloma annulare. Close scrutiny of the interstitial infiltrate on histology and adjunctive immunostaining established the diagnosis as diffuse large B-cell lymphoma (DLBL). This is the first description of B-cell lymphoma mimicking interstitial granuloma annulare clinically and histologically. Cutaneous T-cell lymphoma, in particular the "interstitial" variant of mycosis fungoides, is reported to closely mimic interstitial granuloma annulare. Although the skin histology suggested high grade features,due to the unusual indolent clinical presentation, the patient was monitored clinically.Five years after initial presentation, the patient developed a large fungating skin tumor on the chest wall also confirmed as DLBL. Six cycles of R-CHOP chemotherapy led to complete resolution of the chest lesion and rash. Eighteen months after completion of chemotherapy, he presented to hospital with left-sided weakness. A CT scan revealed a right temporal lobe mass, radiologically most likely lymphoma. The patient declined further treatment and died shortly afterward. This case highlights the importance of long-term follow-up of patients with DLBL, even with a seemingly indolent initial clinical presentation.