Unilateral violaceous/dusky erythematous patches progressing to nodules

Patient description

49 year old man. 

Relevant medical background: Hodgkins lymphoma-first occurrence 2014 axilla. ABVD chemo 4 cycles plus radiotherapy. 

2023- Late recurrence right groin, platinum chemo. August 2023 autologous stem cell transplant

CT scan August 2025 clear. Diabetes with high HBA1C.

Case description

This man developed violaceous/erythematous patches on volar right arm with progression to nodules in some areas more recently. (See pictures). They are asymptomatic. They appeared in April 2025 and have gradually progressed. Clinical differentials when I first saw him included: Paraneoplastic figurate erythema, early cutaneous lymphoproliferative disorder or an inflammatory hypersensitivity reaction. 

Punch biopsy shows: Epidermal involvement with keratinocyte necrosis, interface inflammation and Tcell infiltrate superficial, deep, subcutaneous and periadnexal. Eccrine accentuation resulting in eccrine squamous syringometaplasia. CD30 and CD 15 negative. No T cell lymphoma. Tissue TCR negative. Differentials histologically included hypersensitivity reaction to drug (all his drugs are very long term and unlikely causative (pantoprazole, Sitagliptin, metformin, gliclazide, fenofibrate, lisinopril, bisoprolol, olmesartan.) Last chemo was three years ago. ?Connective tissue /subacute lupus(full screen negative).

Note his recent clear CT scan as well. 

 His protein electrophoresis- shows hypogamaglobulinaemia 5.90 (8-13.50). ESR/CRP normal. LDH normal. 

The interface dermatitis with eccrine-directed toxicity and lobular panniculitis would fit with recent chemo but he hasnt had chemo for 3 years. His autoimmune is negative. I cannot really explain the significant inflammation clinically and histologically. In view of his background it would be difficult to consider immunosupression without a clear diagnosis. 

Your ideas and thoughts are welcome. 

Pics attached of initial presentation and now more recently progression to nodules in the last two pictures.