Role of 18F-FDG PET/CT in patients with pyrexia of unknown origin

Objectives: This paper is a prospective observational study to assess the role of 18F-FDG PET/CT in evaluation of pyrexia of unknown origin (PUO) in a hospital based population in a tertiary level referral center in an Indian metropolitan city. Materials and methods: Medical records of 25 patients who underwent 18FDG PET/CT as a part of investigative work up of PUO were analyzed. A diagnostic CT scan was performed from the level of clavicle to the pubic symphysis in arterial and venous phases of contrast administration. Equilibrium phase images were obtained from vertex to mid-thigh without breath hold instructions with subsequent PET acquisition from vertex to mid-thigh, and these two sets of images were fused to obtain PET/CT fused images. Two radiologists with considerable PET-CT experience evaluated the contrast enhanced CT and 18-FDG PET-CT images separately and tried to identify the probable cause of fever in the 25 patients. Results: Records of 25 patients (13 Females, 12 Males) were evaluated. Abnormal focal FDG uptake was found in 21 patients and contributed to final diagnosis (TP) in 20 patients with 1 false positive results (FP). In the rest of the 4 patients with negative PET/CT final specific diagnosis (FN) was made only in 2 patients (2/4-50%) and in 2 patients no diagnosis was made (TN). The PET/CT had a sensitivity of 90.91%, specificity of 66.67%, positive predictive value (PPV) of 95.24% and negative predictive value (NPV-50%). TP cases included 8 cases of Kochs (2 cases of tubercular lymphadenitis, 1 case of tubercular pleural effusion, 1 case of spinal kochs, 1 case of genitourinary kochs, 1 case of Cutaneous Koch, 1 case of splenic Koch; 1 case of abdominal Koch); 4 cases of focal infections/abscesses, 1 cases of lymphoma, 2 cases of Sarcoidosis, 1 case of Kikuchi Fusimoto, 1 case of aortoarteritis, 1 case of Castleman's disease, 1 case of Rosai Dorfman and 1 case of thyroiditis. FN negative cases included one case of meningitis and one case of giant cell arteritis. One false positive case was due to focal hyper metabolism on PET in the caecum. In comparison, on CECT, probable etiology was suspected in 11 patients, out of which 8 cases were true positive (TP), 3 cases were false positive and 12 were false negative. In 2 patients no diagnosis was made (TN). CECT had a sensitivity of 42.86%, specificity of 50% positive predictive value (PPV) of 84% and negative predictive value (NPV-14.29%). Thus 18F-FDG PET/CT improved the sensitivity (90.91% vs 42.86%), specificity (66.67% vs 50%), Positive predicate value (95.24% vs 84%) and Negative predicate value (50% vs 14.29%) as compared CECT alone. Conclusions: FDG PET/CT is better than CECT in making a specific diagnosis in the evaluation of PUO. It also helps in deciding the best possible site for biopsy