Isolated skeletal muscle recurrence of an originally nodal diffuse large B cell lymphoma: A case report and review of the literature.

Rationale: Diffuse large B cell lymphoma (DLBCL) is a malignancy of the B cells with extranodal primary involvement being estimated at 30% to 40% of cases. Primary skeletal muscle presentation of DLBCL is extremely rare, with an estimated incidence of about 0.5% of extranodal lymphomas, presenting mostly in the lower extremities. The possible mechanisms of muscle involvement of DLBCL include primary extranodal disease, extension from adjacent organs (such as lymph nodes) or disseminated disease. Patient concerns: We report a case of a 70-year-old woman with an advanced initially nodal DLBCL, treated with R-CHOP, that presented with an enlargement of her left thigh and restricted mobility 3 months after completion of chemotherapy. Imaging studies were performed, which showed possible infiltration of the muscles of the left thigh, without any nodal disease present. Diagnoses: Muscle biopsy documented the recurrence of the lymphoma at the left thigh. Interventions: The patient started second-line treatment with gemcitabine and vinorelbine. Outcomes: A partial response was achieved after the first cycle. Lessons: The remarkable element lies in the reappearance of the lymphoma at the left thigh muscles, with no radiographic or clinical evidence of involvement of lymph nodes, despite the extensive lymph node disease at initial presentation. The further management of such recurrences remains to be clarified, as the odd biological behavior of the malignant cells dictates a special handling of the disease.