Eosinophilic granulomatosis with polyangiitis (EGPA) on remission with a new neuropathy: a rare case of mycophenolate induced primary CNS lymphoproliferative disease.

Introduction Mycophenolate Mofetil (MMF), although a widely used immunosuppressant; an increasing concern of MMF induced Primary Central Nervous System Lymphoma (PCNSL) are being reported. Timely diagnosis and management of MMF induced PCNSL can play a vital role in improved outcomes. Case Presentation Eighty-one-year-old female with history of Eosinophilic Granulomatosis with Polyangiitis (EGPA) presented with word finding difficulty, right-hand weakness and right foot clumsiness. EGPA had been stable with MMF for 6 years. Physical examination revealed weakened right-hand grip, positive right-sided dysdiadokokinesia and right foot drop. MRI-brain identified three enhancing solid lesions - in right parietal, left insular and left mid brain extending into the left thalamus. Brain biopsy revealed a focally dense lymphoid infiltrate with CD20 positive B cells, with large atypical cells resembling Hodgkin Reed-Sternberg cells. With concern for immunosuppression related PCNSL, MMF was stopped. Patient was treated with 8 weeks of rituximab therapy for its least toxic profile and concomitant benefit in EGPA. On a 2 month follow up MRI-brain, near total resolution of the intracranial lesion was observed. Patient still had some residual right lower extremity incoordination, however, strength and speech normalized with resolution of dysdiadokokinesia. Patient was advised to discontinue MMF indefinitely and remains on low dose prednisone daily. Conclusion MMF is an inhibitor of Inosine Monophosphate Dehydrogenase which prevents T- and B-cell proliferation. PCNSL is a potential complication of chronic immunosuppression with this medication. Discontinuation of the drug along with immunosuppressive therapies have been the effective therapeutic options till date.