[Seronegativity and anti-CD20: When a treatment compromises the diagnosis].

INTRODUCTION

Lyme borreliosis is suspected when there are compatible symptoms associated with tick exposure. The diagnosis, except for erythema migrans, is based on serology. However, in some cases, serology may be erroneous.

CASE REPORT: A 50-year-old woman treated with obinutuzumab for a lymphoma presented with diffuse erythematous lesions, arthralgias and meningoradiculitis. Initial investigations, including multiple Lyme serologies, were inconclusive. After several hospitalizations, a next-generation sequencing analysis for infectious agents on cerebrospinal fluid was finally positive for Borrelia afzelii. Treatment with ceftriaxone resulted in complete resolution of symptoms.

CONCLUSION

As anti-CD20 treatments are increasingly used in our internal medicine practices, it is important to keep a critical eye on the results of negative serologies in these situations. Direct tests (PCR, cultures, NGS, etc.) should therefore be preferred for diagnosing infections in patients on anti-CD20 therapy in case of a negative indirect test (serology). Furthermore, the absence of seroconversion seems to favor a more severe clinical picture in case of Lyme borreliosis (neurological symptoms), associated with rather rare manifestations (hepatitis, multiple erythema migrans).