An 82-year-old woman was investigated for a 6-month history of weight loss, abdominal pain and diarrhea. A subsequent abdominal CT scan, colonoscopy, and histological specimens of the caecum established a diagnosis of ileo-caecal crohn's disease (CD), and the incidental finding of severe sigmoid diverticulosis. Treatment with sulphasalazine and prednisolone lead to a prompt resolution of symptoms.

The patient was hospitalised on several occasions over the next 12 months for the diagnosis of sigmoid diverticulosis and caecal CD respectively. Multiple CT scans and colonoscopies revealed ongoing caecal inflammation and patchy inflammation in the sigmoid colon. The dual diagnosis of caecal CD and diverticulitis of the sigmoid colon was suggested. Mycobacterium tuberculosis (TB) was considered as a differential diagnosis however acid fast bacilli were not detected on biopsy, the chest X-ray was normal and the quantiferon gold was negative. Due to the recurrent sigmoid diverticulitis accompanied by caecal CD a colectomy was performed.

The unexpected diagnosis of colonic TB was only made following histological assessment of the surgical specimen. Numerous acid fast bacilli (Figure 1) and areas of granulomatous inflammation (Figure 2) were evident. The CT scans taken preoperatively show sigmoid diverticuli and colonic inflammation. This was confirmed at operation—the patient was suffering from both diverticulosis and intestinal TB. CD and intestinal TB both may cause segmental and granulomatous disease of the intestine. Several recent case series help distinguish the two conditions and guide investigation. Importantly, TB is not simply a right-sided disease, with 30% of cases involving the left hemicolon. Radiological and endoscopic features of both conditions may be similar, and organisms are rarely stained or cultured successfully from biopsy specimens (< 10%). Diagnosis may only be possible in some cases following surgical resection or with anti-tuberculous agents causing a resolution of clinical and radiological disease.

Recent advances in medical diagnostic technology hold promise in differentiating intestinal TB and CD. Polymerase Chain Reaction (PCR) may detect mycobacterial DNA in endoscopic biopsy specimens. A large case series reports a sensitivity of 65%, and a specificity > 95% for intestinal TB where biopsies were taken at colonoscopy.

Interferon—gamma release assays (IGRAs), such as QuantiFERON-TB Gold, are now used widely to screen for latent TB. It is not often appreciated however that Interferon Y—assays have been thoroughly tested and validated in cases of active tuberculosis, both pulmonary (and to a lesser extent) extrapulmonary. A sensitivity of 65–95%, with a specificity of approximately 90% has been demonstrated in cases of active TB.

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