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Hypertrophic pachymeningitis (HP) is a rare disorder characterized by dura matter thickening with or without accompanying parenchymal inflammation.  Etiology for HP is broad including infection, neoplasm, autoimmune/inflammatory disease notably including sarcoidosis, Behcet’s and IgG4-related disease and idiopathic

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A 42-year-old male with medical history significant for chronic lymphocytic lymphoma (CLL) diagnosed in Jan 2017, maintained on ibrutinib, a burton tyrosine kinase inhibitor (BTKi), since 2021 with resolution of lymphadenopathy and normalization of hematological profile presented with new expressive aphasia in Sept 2023.  MRI brain w/wo demonstrated diffuse nodular dural thickening & enhancement with significant involvement of left temporoparietal dura and parenchymal edema.  Lumbar puncture revealed WBCs, elevated protein & glucose, flow cytometry with low cellularity - no flow immunophenotypic evidence.  Extensive infection work-up by PCR and NAA was negative.  Extensive serum inflammatory & infectious work-up negative.  Dural biopsy on 9/2023 revealed extensive mixed inflammatory cell infiltrate and areas of central necrosis, no evidence of lymphoma and/or infectious etiology, overall suspicious for hypertrophic pachymeningitis.  He started Decadron 4 mg qd.  MRI brain 11/2023 demonstrated significant improvement in the dural nodularity.  Decadron was decreased to 2 mg.  In Dec 2023, he developed diplopia with a new CNVI palsy & headaches.  Decadron was increased back to 4 mg  qd (max 8 mg qd) without significant improvement.  Ultimately, he started on Rituximab 1000 mg day 1 and day 15 in early Feb 2024 with current clinical and radiographic stability. He has been successfully weaned off Decadron.  

HP requires extensive work-up for inflammatory, infectious and neoplastic etiologies.  This patient underwent this extensive work-up and was grossly unrevealing.   This HP case is the first described on a BTKi.  Despite CLL diagnosis, biopsy did not support HP related to CLL.   At this time, it is not clear if HP was an adverse event caused by the BTKi or idiopathic in nature.