Make the Diagnosis

A 50-year-old White male presented with a 4- to 5-year history of progressively growing violaceous lesions on his left lower extremity

Publish date: April 12, 2023

A 50-year-old White male presented for evaluation of a 4- to 5-year history of progressively growing violaceous lesions on his left lower extremity, unresponsive to over-the-counter treatments.

He denied fever, chills, night sweats, easy bruising, or skin cancer history but noted a 35-pound weight loss over the past 2 years. Physical exam demonstrated multiple clustered erythematous and violaceous patches and nodules on the medial, anterior, and lateral aspects of the left lower extremity.

There was no cervical, axillary, or inguinal lymphadenopathy.

Primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL-LT) is a specific categorization of cutaneous B-cell lymphoma (CBCL) demonstrating a predominance of immunoblasts and centroblasts with scarce T-cells, classically presenting as rapidly progressive, plum-colored lesions on the lower extremities.^1,2 CBCLs, with PCDLBCL-LT accounting for 4%, make up the minority of cutaneous lymphomas in the Western world.^1-3 The leg type variant, typically demonstrating a female predominance and median age of onset in the 70s, is clinically aggressive and associated with a poorer prognosis, increased recurrence rate, and 40%-60% 5-year survival rate.^1-5

Histologically, this variant demonstrates a diffuse sheet-like growth of enlarged atypical B-cells distinctively separated from the epidermis by a prominent grenz zone. Classic PCDLBCL-LT immunophenotype includes B-cell markers CD20 and IgM; triple expressor phenotype indicating c-MYC, BCL-2, and BCL-6 positivity; as well as CD10 negativity, lack of BCL-2 rearrangement, and presence of a positive MYD-88 molecular result.

^{Marlee Hill, University of Oklahoma}

Other characteristic histopathological findings include positivity for post-germinal markers IRF4/MUM-1 and FOXP-1, positivity for additional B-cell markers, including CD79 and PAX5, and negativity of t(14;18) (q32;21).^1,3-5

This case is of significant interest as it falls within the approximately 10% of PCDLBCL-LT cases demonstrating weak to negative MUM-1 staining, in addition to its presentation in a younger male individual.

^{Marlee Hill, University of Oklahoma}

While MUM-1 positivity is common in this subtype, its presence, or lack thereof, should not be looked at in isolation when evaluating diagnostic criteria, nor has it been shown to have a statistically significant effect on survival rate – in contrast to factors like lesion location on the leg versus non-leg lesions, multiple lesions at diagnosis, and dissemination to other sites.2,6

PCDLBCL-LT can uncommonly present in non-leg locations and only 10% depict associated B-symptoms, such as fatigue, night sweats, weight loss, or lymphadenopathy.^2,6 First-line treatment is with the R-CHOP chemotherapy regimen – consisting of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone – although radiotherapy is sometimes considered in patients with a single small lesion.^1,2

Dr. Donna Bilu Martin

Because of possible cutaneous involvement beyond the legs, common lack of systemic symptoms, and variable immunophenotypes, this case of MUM-1 negative PCDLBCL-LT highlights the importance of a clinicopathological approach to differentiate the subtypes of CBCLs, allowing for proper and individualized stratification of risk, prognosis, and treatment.

This case was submitted and written by Marlee Hill, BS, Michael Franzetti, MD, Jeffrey McBride, MD, and Allison Hood, MD, of the University of Oklahoma, Oklahoma City. They also provided the photos. Donna Bilu Martin, MD, edited the column.

Dr. Bilu Martin is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at mdedge.com/dermatology. To submit a case for possible publication, send an email to dermnews@mdedge.com.