VALUE OF TC-99M HMPAO-LABELED LEUKOCYTE SCINTIGRAPHY AS AN INITIAL SCREENING-TEST IN PATIENTS SUSPECTED OF HAVING INFLAMMATORY BOWEL-DISEASE

Objective: This study was designed to evaluate the role of technetium- 99m (Tc-99m) hexamethyl propylene amine oxime (HMPAO)-labelled leucocy te imaging as an initial screening test in patients suspected of havin g inflammatory bowel disease (IBD). Patients and methods: Thirty-one p atients in whom a final diagnosis of irritable bowel syndrome (IBS) wa s made (group 1) and another 33 patients with established Crohn's dise ase (group 2) were studied. All patients had (TC)-T-99m HMPAO-labelled leucocyte scan with imaging al 40 and 120 min. Scans with abnormal bo wer uptake were considered positive and this uptake was quantified by visual grading and computer-based methods (scan score). Group 1 patien ts with positive Tc-99m HMPAO scan underwent an indium-111 ((111)ln)-l abelled leucocyte scan (imaging at 180 min) followed by endoscopy and barium radiology as deemed necessary in order to verify the Tc-99m HMP AO result. Results: Three scan patterns were seen: well localized and unequivocally positive scans at both 40 min and 2 h were obtained from 28 patients. All but one had established Crohn's disease. Diffuse bow el uptake was seen in 14 scans. Ten of these (false positive) were obt ained from symptomatic patients with IBS and four (false negative) fro m patients with asymptomatic Crohn's disease. No bowel uptake at 40 mi n and 2 h was seen in 22 scans. All but two of these (who had quiescen t Crohn's disease) were obtained from patients with IBS. Active Crohn' s disease is associated with significantly higher scan score (mean +/- SEM, 82.1 +/- 13.6) than the false positive scans (12.5 +/- 3.1, P gr eater than or equal to 0.001). Patients with false positive (TC)-T-99m HMPAO scans had negative In-111 scans, endoscopy and barium radiology . Conclusion: Bowel scanning using either In-111 or Tc-99m HMPAO is us eful in excluding active IBD. Because of radiation dose, image quality and availability Tc-99m may be preferred to (111)ln.