# An atypical finding on serum immunofixation: a case report

## TL;DR

A 55-year-old man with unusual serum immunofixation results was diagnosed with oligosecretory multiple myeloma despite typical markers being absent.

## Contribution

Highlights an atypical case of multiple myeloma with unusual serum immunofixation findings and oligosecretory characteristics.

## Key findings

- Serum immunofixation showed unusual unrestricted κ staining in the α-2 region.
- Bone marrow examination revealed approximately 90% plasmacytosis.
- Matrix-assisted laser desorption/ionization mass spectrometry identified only polyclonal κ SFLC.

## Abstract

Multiple myeloma (MM) is characterized by the abnormal proliferation of plasma cells, resulting in the overproduction of distinctive monoclonal proteins (M-protein). Suspected MM necessitates screening for M-protein through a combination of serum protein electrophoresis, serum immunofixation (SIFE), and serum free light chain (SFLC) determination. An M-protein appears as a relatively restricted band on agarose gel, where migration in ɑ-2 is rare.

A 55-year-old man with pulmonary tuberculosis presented with severe lower back pain. On examination, he appeared chronically ill, with conjunctival pallor. X-rays revealed vertebral compression fractures. The full blood count confirmed anemia; however, serum calcium and creatinine levels did not meet myeloma-defining event criteria.

The serum protein electrophoresis revealed hypogammaglobulinemia, with the SIFE demonstrating unusual unrestricted κ staining in the ɑ-2 region. A markedly elevated κ SFLC and κ:λ ratio were found. Bone marrow examination demonstrated approximately 90% plasmacytosis. Urine immunofixation revealed a small, restricted κ band disproportionate to the κ SFLC. Notably, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry identified only polyclonal κ SFLC.

Given the absence of a discernible M-protein on SIFE, a small κ restriction on urine immunofixation, and a polyclonal increase in κ SFLCs, the patient’s condition is being managed as an oligosecretory MM.