Case report: Monoclonal gammopathy of undetermined significance is associated with Loa loa infection

A 63-year-old woman who migrated from Nigeria to the United States was found to have an elevated total serum protein, anemia, and eosinophilia. Serum protein electrophoresis (SPEP) and serum protein immunofixation electrophoresis (SPIFE) demonstrated monoclonal immunoglobulin G (IgG) κ restricted bands (IgG 3,820 mg/dL; κ/λ ratio 4.47), indicative of monoclonal gammopathy of unknown significance (MGUS). A rapid diagnostic test (RDT) for malaria was positive for Plasmodium falciparum (BinaxNOW®; Alere Scarborough Inc., Scarborough, ME). Giemsa-stained blood smears were negative for malarial parasites, however, Loa loa microfilariae were identified. Reverse transcription polymerase chain reaction for P. falciparum, Plasmodium ovale, Plasmodium malariae, and Plasmodium vivax yielded a negative result. She was treated for loiasis with diethylcarbamazine and received no malaria medication. Treatment resulted in a resolution of the microfilaremia and eosinophilia, a negative RDT for malaria, and marked reduction in the monoclonal gammopathy. This is the first reported human case of MGUS associated with loiasis and its resolution after antiparasitic treatment.