E162 Granulomatosis with polyangiitis manifesting as hypertrophic pachymeningitis

Background/Aims Hypertrophic pachymeningitis (HP) is a rare chronic inflammatory disorder with dural thickening with wide differential such as IgG4-related disease, neurosarcoidosis, infection, malignancy, and systemic autoimmune conditions such as granulomatosis with polyangiitis (GPA). GPA is an ANCA-associated small-vessel vasculitis affecting multiple organs, including the central nervous system. HP is uncommon but may present early in the course of ANCA vasculitis, especially with MPO antibodies. This case illustrates a diagnostically challenging GPA presentation with hypertrophic pachymeningitis, complicated by overlapping features of malignancy. Methods This case report describes a 63-year-old man presenting with a six-month history of persistent headaches initially diagnosed and treated as trigeminal neuralgia. An early non-contrast CT head was reported as possible subarachnoid haemorrhage. MRI brain demonstrated diffuse pachymeningeal thickening. He was referred to rheumatology for further assessment. On review, he reported additional symptoms of hearing loss, recurrent sinusitis, nasal crusting, and weight loss, raising suspicion of a vasculitis process, prompting comprehensive investigations. Results Blood tests revealed a raised PR3 of 11 IU/mL; lumbar puncture excluded CNS infection. The IgG subclasses showed a mild increase in IgG4. PET-CT demonstrated periaortitis in the abdominal aorta and abnormal metabolic uptake in the right tonsil, and subsequent tonsillectomy confirmed a localised squamous cell carcinoma (T1N0M0). The lymph nodes were clear of any malignant spread outside the tonsil. A nasal mucosal biopsy Rt ethmoid uncinate process showed extravascular granulomatous inflammation, suggestive of GPA. There was no perineural invasion of cancer. A biopsy of the dura was thought to be too invasive; therefore, he was treated as vasculitis with CNS involvement. He was started on oral corticosteroids and azathioprine, with marked improvement in the headache and ENT symptoms. Conclusion This case exemplifies a challenging presentation of GPA with CNS involvement of meninges (HP). It becomes more complicated due to the presence of malignancy. The HP due to GPA tends to have more extra-neurological involvement (sinus, periaortitis in our case) and diffuse changes on MRI compared to HP related to malignancy, where less extra-neurological involvement and focal changes on MRI are the main features. In conclusion, GPA remains an important cause of hypertrophic pachymeningitis. Disclosure S. Thapa: None. M. Ghaffar: None. D. Makkuni: None.