Mycobacterium Genavense Presenting as Mesenteric Mass and Chylous Ascites

Introduction/Background:

Mycobacterium genavense is a slow-growing non-tuberculous mycobacterium that is rarely seen in patients with HIV and immunodeficiencies. It is more often seen in patients with CD4 count less than 100, but not exclusively. Clinically, patients often experience diarrhea, abdominal pain, may have hepatosplenomegaly, and lymphadenopathy. Chylous ascites has been reported, this is thought to be due to blood vessel and lymphatic compression by a mesenteric mass. It has been suggested that M. genavense causes a specific syndrome of retractile mesenteritis, duodenal thickening, and central mesenteric mass. M. genavense does not grow in solid media and has a long incubation period with a median delay of 7 weeks. Radiological features include mesenteritis, duodenitis, and bowel thickening. There is often abdominal lymphadenopathy, and a central mesenteric mass. Treatment involves long courses of antibiotics, often including macrolide, rifamycin, and a fluoroquinolone.

Description:

A 44-year-old male with a history of HIV and prior Mycobacterium avium infection was admitted to the hospital for abdominal pain, significant chylous ascites and a spiculated mesenteric mass seen on CT. He recently had drains placed to control his ascites and had a copious amount drained in the prior week. His CD4 count at admission was 77 with an undetectable viral load. The mass was concerning for a malignant tumor, though evaluation revealed normal tumor markers. Biopsy of the mass demonstrated non-caseating granulomas and a positive acid-fast bacilli (AFB) smear. He was discharged with clarithromycin, ethambutol, and rifabutin. The AFB culture taken of the mass grew Mycobacterium genavense after 30 days. Antibiotics were adjusted to clarithromycin, moxifloxacin, and rifabutin. These were discontinued after 4 years as his symptoms improved and follow up CT abdomen demonstrated resolution of ascites. 2 years later he redeveloped chylous ascites and abdominal pain. Clarithromycin and moxifloxacin were restarted. CT abdomen showed a partially calcified central mesenteric mass with retraction of the abdominal mesentery and duodenum. Patient continues to take antibiotics with control of his symptoms.

Discussion:

This case demonstrates a rare infection seen in HIV patients. It is important to consider this infection in HIV patients with a positive AFB smear and negative cultures due to the long incubation period. Further research is needed to find an optimal antibiotic regimen.