QUITMAIN MENU

HDF Case 951854 MYCOB ATYP INTEST

44 yo male with severe diarrhea. Known positive HIV, Gastroscopy and colonoscopy normal, with suspicion of angiodysplasia.

Endoscopic biopsy of stomach, duodenum and colon.

QUITMAIN MENU

Section from the duodenum demonstrates enlarged, clubbed intestinal villi.

QUITMAIN MENU

Enlargement of the villi is due to a homogenous cellular infiltrate,

QUITMAIN MENU

Higher magnification, the infiltrate is formed by cells having an abundant eosinophilic cytoplasm, with a regular nuclei.

QUITMAIN MENU

On higher magnification, the cytoplasm is somewhat granular.

QUITMAIN MENU

PAS Stain discloses cytoplasmic positivity.

QUITMAIN MENU

Acid fast stain discloses numerous intracytoplasmic bacilli.

QUITMAIN MENU

DIAGNOSIS

ATYPICAL MYCOBACTERIOSIS CONSISTENT WITH MYCOBACTERIUM AVIUM INTRACELLULARE INFECTION

Biopsy of the colon

QUITMAIN MENU

Low power, changes are inconspicuous, slight increase in the inflammatory infiltrate of the lamina propria

QUITMAIN MENU

Higher magnification of previous field. Non specific infiltrate.

QUITMAIN MENU

The infiltrate is mainly mononuclear, with macrophages.

QUITMAIN MENU

Higher magnification on the infiltrate.

QUITMAIN MENU

PAS stain demonstrates cytoplasmic, non specific, granular positivity

QUITMAIN MENU

Acid fast stain discloses positivity in some areas.

QUITMAIN MENU

Intensity of staining contrasts with the weak positivity to PAS,

QUITMAIN MENU

The presence of the bacilli, unremarkable on HE and PAS stain, should be suspected in the clinical setting, and detected with an acid fast stain.

QUITMAIN MENU

Myobacterium Avium-IntracellularePATHOGENESIS AND CLINICAL FEATURES

• In AIDS, disseminated infection with M. avium-intracellulare is common as a preterminal event. Formerly it was documented to be a rare opportunist in man, causing lung disease in adults and cervical lymphadenopathy in children.

• Evidence of disseminated infection may be heralded by sustained bacteremia, but involvement of other organs may be the first signal of the presence of this disease. Involvement of the spleen, lymph nodes, and bone marrow is common. The liver and gastrointestinal tract are also commonly affected, but infection in the latter is patchy and is not usually the initial site that is recognized.

• Only rarely is there such massive infiltration of the gastrointestinal tract that diarrhea and malabsorption can be attributed to infection with M. avium-intracellulare.

QUITMAIN MENU

PATHOLOGY

• The endoscopic appearance of the mucosa may be normal or reveal thickened folds, macular color changes, plaques, or shallow ulcerations. Transmural involvement may be suggested by strictures in the small bowel, seen with barium Xrays.

• The histology is characterized by variably sized sheets of macrophages. Caseation necrosis and epithelioid giant cells are absent. If there is extensive macrophages infiltration, small intestine villi may appear clubbed or, rarely, totally flat.The macrophages are large, rounded. Some appear foamy but not as prominently so as in Whipple's disease, nor do they contain as much lipid. There is little or no cellular reaction surrounding the macrophage collections. Acid-fast stains are positive. These macrophages are also periodic acid-Schiff (PAS) positive and diastase resistant.

QUITMAIN MENU

DIFFERENTIAL DIAGNOSIS

• It is not uncommon to see small collections of macrophages in the gut of AIDS patients. In these instances acid-fast stains are done, but they are frequently negative.

• M. avium-intracellulare infection may resemble Whipple's disease but is easily differentiated from it with acid-fast stains. A few patients with AIDS have been described who have an intestinal lesion similar to Whipple's disease and M. avium, but in whom the foamy macrophages did not contain acid-fast organisms but rather gram-positive bacilli. These probably represent infection with Corynebacterium. It is also likely that other organisms, such as salmonella and shigella, can remain viable within defective phagocytic cell.