FRI217 False Negative Plasma Metanephrines In A Patient With A Bladder Paraganglioma

Abstract

Abstract Disclosure: T.F. King: None. G. Sng: None. T. Puar: None. Introduction: Both plasma free metanephrines and urinary metanephrines have high (>90%) sensitivity to detect phaeochromocytoma and paragangliomas (PPGL). False positive urine metanephrines are seen in many conditions including obstructive sleep apnoea (OSA), and plasma metanephrines have been proposed to be a useful diagnostic tool in this patient population. Clinical Case: A 53 year old female was recruited into a study evaluating the utility of plasma and urine metanephrines in the diagnosis of PPGL in patients with OSA. She had a 6 year history of hypertension that was well controlled with amlodipine 5mg daily. She had no headache, palpitations or paroxysmal symptoms. She had 3 previous uneventful pregnancies and there was no significant family history of note. She was overweight (BMI 28.3 Kg/m2) and blood pressure was 130/80 mmHg. Sleep studies revealed severe OSA. Screening plasma and 24 hour urine metanephrines were performed at baseline and again after 6 months (Table 1). 24 hr Urinary normetanephrine, mcg/day (Upper Reference interval 423): Baseline 437, Visit 2 (Six Months later) 535, Post-operative 235. Table 1. Serial measurements of urine and plasma metanephrines. In view of the persistently elevated urinary normetaneprine, a CT abdomen and pelvis was performed. This revealed normal adrenal glands, but an avidly enhancing 2cm focal nodular lesion was seen at the left lateral posterior wall of the urinary bladder. Transurethral biopsy revealed a tumour with immunohistochemistry positive for synaptophysin and GATA3, consistent with a paraganglioma. A CT/PET Ga68 dotatpeptide scan showed intense uptake in the same area with no evidence of lymphadenopathy or distant disease. Amlodipine was changed to terazosin pre-operatively and the patient went on to have an uneventful robot assisted excision and partial cystectomy. Histology was consistent with a bladder paraganglioma with clear tumour margins. Genetic analysis for hereditary PPGL was negative for mutations in SDHx, VHL, RET, NF1, but there was a variant of uncertain significance in the MUTYH gene, namely c.767C>T (p.Thr245Ile). At two months post-operative review, the patient remained well and home blood pressure readings were all >120/80mmHg on 5mg amlodipine. Repeat urine and plasma metanephrines were normal. Conclusions: Plasma metanephrines may not be sensitive enough to detect small asymptomatic bladder paragangliomas. Further studies are warranted to elucidate the optimal diagnostic tests in patients with sleep apnoea and suspected PPGL. Interval measurements of metanephrines may be useful in the diagnosis of small PPGL that may manifest with time. Presentation: Friday, June 16, 2023