A BIOPSY-VERIFIED CASE OF CENTRAL NERVOUS SYSTEM INVOLVEMENT OF MYCOSIS FUNGOIDES WITH POSITIVE RT-QUIC ASSAY

Abstract

Introduction: We report a rare case of positive RT-QuIC assay in CNS involvement of mycosis fungoides.

Case presentation: A 73-year-old man presented with decreased consciousness and generalized convulsions. He had been formerly diagnosed with mycosis fungoides, by that time in full remission. Clinical examination revealed profound cognitive deficits with fluctuating level of alertness during admission. An MRI of the brain showed multiple contrast-enhancing lesions in both hemispheres, while lumbar puncture indicated lymphocytic pleocytosis with elevated CSF protein. The rapidly progressive cognitive decline prompted investigations for Creutzfeldt-Jakob disease (CJD) with 14-3-3 and RT-QuIC assay, both of which came back positive. Meanwhile, flow cytometry analysis reported increased T-cell population, suggestive of CNS lymphoma. Despite the high specificity of the RT- QuIC assay for CJD, the diagnosis was not further supported by imaging or EEG findings. A brain biopsy was performed, reporting brain infiltration by a highly malignant T-cell lymphoma, believed to represent large cell transformation of mycosis fungoides with CD30 expression. Treatment with pulsed steroids had some effect on the level of consciousness, although a degree of memory impairment remained.

Conclusion: Positive RT-QuIC assay has been strongly linked to CJD, with specificity reaching 99%. This case highlights the possibility of positive RT-QuIC results associated with CNS lymphoma.