Case Presentation: An 83-year-old man visiting from rural Mexico, presented with one-month-old diffuse, painful, multinodular subcutaneous lesions with a pruritic rash on the left leg. A week prior to admission, the patient reported new inguinal and upper extremity lesions and a violaceous, pruritic, non-painful, maculopapular rash at the waistband with progression to the upper arms. The patient reported a penetrating injury to the sole of the left foot prior to the signs and symptoms seen on admission.
Exam demonstrated multiple firm, nodular and tender lesions of the lower extremities, inguinal region, and torso with shoulder, arm, and right eyebrow involvement, without induration, fluctuance, erythema or skin breakdown. A diffuse maculopapular pruritic rash was also noted on the abdomen and flexor surfaces of the elbows.

Initial differential diagnoses included infectious disease, lymphocutaneous disease, disseminated granulomatous infection, and underlying malignancy. Labs revealed an elevated c-reactive protein of 47.8 mg/L and the CBC with differential demonstrated monocytosis, eosinophilia and an erythrocyte sedimentation rate of 33 mm/hr.

The patient had a CT without contrast from a surrounding hospital that revealed soft tissue and subcutaneous nodules on the lower extremities, inguinal region, and periumbilical region. Point-of-care ultrasound was also used to identify the location and size of the nodules. The surgical team was consulted for nodule and skin excisional biopsy, with results sent for a histopathological report that revealed tissue expression of the distinguishing cell markers: CD20, BCL-2, BCL-6, and MUM-1 with a markedly elevated Ki-67 index.

Based on the clinical presentation and pathology report, the patient was diagnosed with primary cutaneous diffuse large B-cell lymphoma (PCDLBCL), leg type (LT) and referred to the hematology and oncology service for aggressive treatment.

Discussion: This patient’s history of a penetrating foot injury, and the location of nodules that extended beyond his legs, in the setting of eosinophilia, initially suggested an infectious disease etiology. Negative blood serologies, microscopy, and cultures directed the diagnosis towards a malignant process.

PCDLBCL, LT is an aggressive form of primary cutaneous B-cell lymphoma (CBCL) distinguished by red-brown to bluish lesions observed primarily on the legs, while 10% to 15% of patients have lesions in other locations. It makes up about 10% to 20% of all primary CBCL diagnoses and 1% to 3% of all cutaneous lymphomas, while presenting in patients at a mean age of 70 years old, and a male to female ratio of 1:3-4.

PCDLBCL, LT is diagnosed clinically with confirmation by histopathology and immunohistochemical staining that reveals a dense and diffuse infiltrate through the dermis and subcutis that can extend to the dermoepidermal junction. This infiltrate is made up of confluent sheets of large B-cells with round nuclei and prominent nucleoli and include centroblasts and immunoblasts.

Due to the aggressive nature of this illness, systemic chemotherapy with possible radiation therapy, depending on the staging, location, and number of lesions present, is the preferred approach of treatment. Prognosis for PCDLBCL, LT has an estimated 5-year survival rate of approximately 50%.

Conclusions: PCDLBCL, LT is a rare and aggressive form of CBCL that can lead to death if undiagnosed. To ensure prompt treatment, a physician should not hesitate to order a biopsy to support the clinical clues needed for this diagnoses.