E160 Discordant C-reactive protein in granulomatosis with polyangiitis: fluorine-18 FDG PET-CT unmasks inflammatory cardiomyopathy

Abstract Background/Aims Granulomatosis with polyangiitis (GPA) is a rare, necrotising vasculitis of small- to medium-sized vessels that classically involves the upper and lower respiratory tracts and kidneys. While systemic inflammation is characteristic, persistently elevated inflammatory markers despite appropriate therapy should trigger evaluation for alternative or atypical causes. We report a GPA case in which symptoms improved on standard treatment, yet C-reactive protein (CRP) remained high. 18F-FDG PET-CT provided the decisive diagnostic signal of myocardial inflammation, unmasking GPA-associated inflammatory cardiomyopathy and changing management. Methods A 68-year-old woman with c-ANCA/PR3-positive GPA (diagnosed in 2023 after constitutional symptoms and mononeuritis multiplex) received CYCLOPS intravenous cyclophosphamide plus reduced-dose glucocorticoids (PEXIVAS), then azathioprine maintenance. Following a flare, she was re-induced with rituximab and commenced avacopan. On referral in September 2024, she denied respiratory or renal symptoms but reported intermittent palpitations and dizziness. Examination was normal except for longstanding bilateral leg oedema and established foot drop. The patient’s C-reactive protein (CRP) remained persistently elevated, fluctuating between 84 and 115. 2 mg/L (normal 5 mg/L), accompanied by a raised white cell count (WCC) of 12. 58 ×10⁹/L (normal 4. 0 - 11. 0 x 109/L). This sustained elevation over three months was unusual in an otherwise asymptomatic patient with well-controlled GPA. Infection and malignancy were excluded (COVID-19 negative, normal urinalysis, chest X-ray, and CT chest/abdomen/pelvis). Further investigation with a whole-body 18F-FDG PET-CT demonstrated four-chamber myocardial uptake, prompting cardiology evaluation. Echocardiography showed severe left-ventricular systolic dysfunction. A CT coronary angiogram confirmed normal coronary arteries with no evidence of vasculitis involvement. Cardiovascular MRI confirmed severe left ventricular dilatation with moderate global systolic dysfunction (LVEF 43%), myocardial oedema, and small areas of non-ischaemic late gadolinium enhancement, consistent with inflammatory cardiomyopathy most likely related to GPA. Results Treatment was escalated with nine further cyclophosphamide pulses, transition to mycophenolate mofetil maintenance, and guideline-directed heart-failure therapy (bisoprolol, empagliflozin, losartan, and furosemide). CRP normalised and clinical status improved; prednisolone was tapered. Conclusion Cardiac involvement in GPA is uncommon, often subclinical, and prognostically important. PET-CT functioned as the problem-solving test, supplying the first objective evidence of active myocardial inflammation when clinical assessment, serology, and conventional imaging were non-revealing. PET-positive myocardium then directed definitive phenotyping with echocardiography and CMR and triggered targeted treatment, achieving biochemical remission. In GPA with biomarker-symptom discordance, early consideration of 18F-FDG PET-CT can shorten time-to-diagnosis and alter outcomes. Disclosure S. Rentala Venkata: None. M. Ashraf: None. A. Ahmed: None.