022. CAN GIANT CELL ARTERITIS PROGRESS TO MICROSCOPIC POLYANGIITIS?

Abstract

Background: We discuss 2 cases of biopsy-positive giant cell arteritis (GCA) that later went on to develop features of Microscopic Polyangiitis (MPA) with high ANCA titre. Methods: 1: A 71 yr lady presentated in 2008 with symptoms of occipital and parietotemporal headache. All symptoms initially disappeared on steroid therapy started by GP for suspected PMR. However, she re-presented 3 months later, after her prednisolone was reduced, with recurrence of headache, eye symptoms, diplopia, high ESR (96) and CRP (128). At this point she had developed jaw pain, worse on chewing and scalp tenderness. Biopsies showed focal infiltration of the adventitia by inflammatory cells extending through the media with disruption of internal elastic lamina, consistent with GCA. She was treated with 60mg of prednisolone and methotrexate. However, her headache persisted, with high inflammatory markers. MRI of the brain showed no signs of meningial enhancement. Patient had a mildly positive ANCA, but repeat was negative. In 2009 she was started on IV methylprednisolone and IV cyclophosphamide followed by methotrexate. This produced significant improvement in her symptoms. In 2014 methotrexate was discontinued because of suspected lung fibrosis. In 2016 she re-presented with myalgia, worsening arthralgia, weight loss and numbess of the left foot and a marked increase in inflammatory markers. 2: A 77 year old lady presented with classical GCA-like symptoms of temporal headache, scalp tenderness and features of PMR. TAB was reported as consistent with active giant cell arteritis. She responded well to highdose steroids but 2 years later, while on a very low dose of steroids started to get redness and pain in the left eye suggestive of sectorial scleritis usually seen in ANCA vasculitis. Results: Case 1: Repeat blood test showed a strongly positive MPO titre of 44. There was no active urinary sediments and her RFT was normal. A diagnosis of MPA was considered at this point and she was treated with further IV cyclophosphamide. Unfortunately her inflammatory markers flared again despite cyclophosphamide. She has therefore been commenced on Rituximab with very good results. Case 2: MPO titre came back strongly positive (>135), suggesting MPA. Symptoms improved with higher dose of steroids. Conclusion: Microscpic polyangiitis is well known to cause necrotizing inflammatory changes in the temporal artery mimicking GCA. However the progression of the disease especially in the second case suggests the appearence of medium or small vessel vasculitis in a patient with pre-exisiting GCA. This suggests an evolution in the condition's natural history although could also be coincidental. We need careful and uniform reporting of temporal artery histopathology to avoid diagnostic pitfalls. Biopsy-positive GCA patients should be carefully monitired to look for any features of other systemic vasculitis developing especially during the withdrawal of their immunosuppressive medications.