Primary cutaneous anaplastic large cell lymphoma arising from a long-standing erythema nodosum: A case report.

Rationale: Primary cutaneous anaplastic large cell lymphoma (pcALCL) is a rare subtype of non-Hodgkin lymphoma, which is rarely associated with erythema nodosum (EN).
Patient Concerns: A 57-year-old woman complained of recurrent rashes involving her abdomen, back, upper and lower limbs for over 20 years, with severity in symptoms for 2 weeks.
Diagnoses: The first skin biopsy was performed in 2011 in another hospital and she was diagnosed idiopathic EN. The second skin biopsy was performed in 2014 and she was diagnosed as pcALCL with stage IA.
Interventions: She was treated with oral prednisone, cyclosporine, and thalidomide.
Outcomes: One month later, the ulcerative lesion was decreased in size and became smooth and the patient achieved partial remission. She is still under treatment and has been monitored closely for 4 years.
Lessons: The case suggested that stimulation of inflammation in the skin lesions for a long period might be related to clonal transformation into pcALCL and hence should be closely monitored. Immunosuppressive treatment may be effective and safe for patients with pcALCL at early stages.