# Low-grade B-cell non-Hodgkin lymphoma in the sternocleidomastoid muscle: a case report and review of literature

## TL;DR

A rare case of low-grade B-cell lymphoma in a neck muscle is reported, highlighting the need for detailed testing for accurate diagnosis.

## Contribution

This is the first reported case of low-grade B-cell NHL in the sternocleidomastoid muscle.

## Key findings

- A 67-year-old male had a slowly growing neck mass diagnosed as low-grade B-cell NHL.
- Immunohistochemistry and molecular testing confirmed extranodal marginal zone lymphoma.
- The patient was managed with active surveillance due to the indolent nature of the disease.

## Abstract

Primary non-Hodgkin lymphoma (NHL) arising in skeletal muscle is exceedingly rare. We present a case of low-grade B-cell NHL involving the sternocleidomastoid muscle. A 67-year-old male presented with an asymptomatic, slowly growing left neck mass. Imaging revealed a 17 mm × 11 mm intramuscular nodule, initially suggestive of a benign lesion. Excisional biopsy demonstrated lymphoid proliferation with muscle infiltration. Immunohistochemistry revealed CD20(+), PAX5(+), BCL2(+), and monoclonal IgH rearrangement, consistent with low-grade B-cell NHL, most likely extranodal marginal zone lymphoma (ENMZL), non-gastric/non-cutaneous type. Staging confirmed Lugano stage I disease. Given the indolent nature, the patient was managed with active surveillance. This case highlights an unusual intramuscular presentation of NHL, emphasizing the importance of histopathological and molecular evaluation for accurate diagnosis and tailored management.