gallium citrate-67 single-photon emission computed tomography/computed tomography for localizing the foci of classic fever and inflammation of unknown origin: a retrospective study of diagnostic yield

Objective(s): only few studies have assessed the use of gallium citrate-67 single-photon emission computed tomography/computed tomography (67ga-spect/ct) for localizing the foci of classic fever of unknown origin (fuo) and inflammation of unknown origin (iuo). hence, the current study aimed to assess the diagnostic contribution of 67ga-spect/ct in a tertiary referral setting where nuclear imaging tests are performed after an unsuccessful comprehensive primary diagnostic workup. methods: we retrospectively assessed the medical records of 27 adult patients with fuo/iuo who had an unsuccessful diagnostic workup and who underwent 67ga-spect/ct for the localization of fuo/iuo foci in our university hospital between 2013 and 2019. the primary outcome was diagnostic yield. the secondary outcomes were overall clinical efficacy and spontaneous remission of fuo/iuo symptoms in patients with a negative 67ga-spect/ct finding.results: almost all patients completed the recommended diagnostic workup, except for urine culture and abdominal ultrasonography. moreover, prior to 67ga-spect/ct, all patients underwent thoraco-abdominopelvic ct scan, which was a non-diagnostic procedure. after a median follow-up of 843 days, the cause was identified in 16 (59%) patients. 67ga-spect/ct successfully localized the fuo/iuo foci in eight patients (diagnostic yield = 30%; 95% confidence interval [ci]: 14%–50%). however, the causes remained unknown during follow-up in 11 (41%) patients. among them, five experienced spontaneous regression of symptoms. 67ga-spect/ct was negative in four of the five patients with spontaneous regression in symptoms without a definite cause. considering this an important event, the overall clinical efficacy of 67ga-spect/ct increased to 44% (95% ci: 25%–65%). conclusion: 67ga-spect/ct had an acceptable diagnostic yield for the localization of fuo/iuo foci, which are challenging to diagnose, in a contemporary tertiary referral care setting. in patients who experienced spontaneous regression in symptoms with an unexplained cause, the absence of abnormal uptake might indicate prospective spontaneous remission. thus, 67ga-spect/ct could be an active first-line nuclear imaging modality in settings where fluorine-18-fluorodeoxy glucose positron emission tomography and computed tomography is not available for the assessment of fuo/iuo causes.