This brief case report serves to highlight the unusual presentation of granulomatosis with polyangiitis as a brain mass.GPA is a necrotizing granulomatous vasculitis affecting predominantly small vessels. GPA usually affects the upper respiratory tract, lungs, kidneys and occasionally nervous system. CNS involvement is extremely rare, representing 7–11% of GPA patients. ₍₁₎

1. (1)Gonzalo de Luna, et al. Central nervous system involvement of granulomatosis with polyangiitis: clinical–radiological presentation distinguishes different outcomes, Rheumatology, Volume 54, Issue 3, 1 March 2015, Pages 424–432, 

Case report of young man with clinical and radiological features suggestive of tumefactive MS vs CNS lymphoma masquerading cerebral GPA.

This case report describes a 18-year-old man with no significant medical history who presented with acute onset truncal ataxia and dysarthria.Brain MRI with contrast showed right periventricular parieto-occipital and right cerebellar hemisphere/vermis mass enhancing lesions with vasogenic edema. MRI of spine did not show any lesions. CSF was mildly inflammatory with elevated protein and lymphocytic pleocytosis.Serum markers were unrevealing, including c-ANCA. Initial biopsy documented 1/6 specimens showing demyelination. Initial thoughts pointed to tumefactive MS, CNS lymphoma and sarcoidosis. CT scan of chest showed lung nodules, groundglass opacities and axillary lymphadenopathy. PET scan showed hypometabolism in the brain lesions which pointed away from malignancy. Repeat biopsy showed demyelination with non-caseating granuloma and lymphoplasmacytic inflammation.Patient was empirically given pulse dose with methylprednisolone which improved dysarthria and ataxia. He was then transitioned to an oral prednisone taper, and subsequently started management with cyclophosphamide. 

ANCA negative GPA is a rare and treatable differential diagnosis for patients with brain mass lesions.