Abstract Background/Aims Granulomatosis with polyangiitis (GPA) can pose multiple diagnostic and therapeutic challenges, especially in patients with negative antineutrophil cytoplasmic antibody (ANCA). We present the case of an atypical ANCA-negative GPA masquerading as giant cell arteritis (GCA) on initial presentation. Methods An 82-year-old Afro-Caribbean male presented in August 2024 with headaches, fevers, visual blurring, scalp tenderness and jaw claudication. Bloods showed CRP 332mg/L, positive c-ANCA, but MPO-ANCA and PR3-ANCA negative. Temporal artery ultrasound (TAUS) showed a bilateral halo sign. There were no ophthalmic neuroischaemic complications. He was treated as GCA with 60mg prednisolone, but was later given three pulses of intravenous methylprednisolone due to slow resolution of inflammatory markers and headache. He improved and was discharged. He was readmitted in August 2025 after a collapse, with rigours, drowsiness, headaches, blurred vision, left eye periorbital oedema, significant ptosis and proptosis. He had stopped steroids for GCA 3 weeks prior to this admission of his own accord. Investigations revealed acute kidney injury (Creatinine 407µmol/L, baseline 89µmol/L), haematuria and proteinuria, CRP 433mg/L (previously normal). There was no clinical or biochemical response on day 7 of antibiotics, and infection was ruled out. CT scan of orbits showed asymmetric thickening of the left orbit subcutaneous tissue. His clinical picture was revised as GPA with pseudotumour cerebri and renal involvement, and was treated with methylprednisolone intravenously, intravenous cyclophosphamide and avacopan. He made a steady recovery, orbital manifestations resolved, and there was improvement in CRP (13 mg/L) and Creatinine (173 µmol/L) after 20 days. Results Orbital proptosis and chemosis can occur in GPA as a relatively rare complication, found in about 15% of cases. Conversely, there are few reported cases of orbital inflammation during a GCA relapse. Notably, there are several reported cases showing overlap between GCA and small vessel vasculitis (GPA and eosinophilic GPA), with orbital and temporal artery involvement. GCA diagnosis has to be reconsidered when there are atypical features, such as in this case. Firstly, GCA incidence in black ethnicity is rare. Secondly, the initial slow gradual response to oral steroids and the subsequent clinical picture does not fit with GCA. Thirdly, renal involvement is unusual for GCA. Overall, approximately 10% of patients with GPA are ANCA negative. ANCA negative cases tend to have more limited disease presentation and tend not to involve the kidneys, unlike in this case. A tissue biopsy can provide valuable information; however, this could not be done in our case prior to starting treatment, as the patient was on anticoagulation and had significant drowsiness. Conclusion GPA presenting with large vessel vasculitis features, ophthalmic presentation, with negative ANCA, can lead to initial diagnostic dilemmas. This case highlights the importance of interrogating the diagnosis when there are atypical features. Disclosure C. Musat: None. S. Carlson: None. B. Gurung: None. C. Yee: None.
Musat et al. (Wed,) studied this question.
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