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TB Peritonitis

posted Dec 16, 2013, 6:35 AM by Eliany Mejia   [ updated Dec 16, 2013, 6:35 AM ]

On Wednesday during CRS, we heard an interesting case of a 34 year old gentleman who presented to Montefiore last year with five days of abdominal pain, later found to have extrapulmonary tuberculosis involving the peritoneum and pleural cavity.

I had the opportunity to review the case as well as some of the literature on tuberculosis peritonitis, a diagnosis that some of us encounter during our work in Uganda but rarely here in the Bronx.

Epidemiology

In the United States, TB peritonitis is one of the rarer presentations of tuberculosis, accounting for only 3.5% of all cases of extrapulmonary tuberculosis.  Known risk factors include coexisting HIV infection, ESRD on peritoneal dialysis, and cirrhosis, the latter condition which can often make the diagnosis more difficult to make.  Interestingly, 62% of patients with TB peritonitis have coexisting alcoholic liver disease (which our patient from CRS had as well).  The most common age group to receive the diagnosis of TB peritonitis is 35-45, possibly related to the prevalence of the known risk factors.  There seems to be a decline in the incidence of TB peritonitis worldwide, which is attributed to less ingestion of unpasteurized milk and tuberculosis testing of dairy herds, which may lead to less direct involvement of tuberculosis in the gastrointestinal tract.

Etiology

The mechanism of tuberculosis infection of the peritoneal cavity is either through direct inoculation by the bacilli from TB involvement of intra-abdominal lymph nodes or organs, or through hematogenous spread, generally from latent or active pulmonary disease.  Interestingly, it is fairly rare for TB peritonitis to present together with active pulmonary disease.  Patients with defects in cell-mediated immunity (HIV, ESRD, etc.) or with malnutrition (cirrhosis, alcoholic liver disease, etc.) are at higher risk for tuberculosis infection.

Clinical Features

Generally, tuberculosis peritonitis has a sub-acute presentation (weeks to months), although patients with cirrhosis may present even later.  One of the frustrating aspects of our CRS case was the fairly acute onset of our patient’s symptoms, which seems rather atypical for TB peritonitis – it is possible that on further questioning, the patient may have admitted to a longer duration of symptoms than on initial presentation.  Common symptoms on presentation include abdominal pain (65% of patients), weight loss (61%), fever (59%), diarrhea (21%), and constipation (11%).  On exam, the findings to look for include ascites (73% of patients), abdominal tenderness (48%), hepatomegaly (28%), and splenomegaly (14%).

Diagnosis

Unfortunately, the diagnosis of TB peritonitis is often elusive.  The CBC may show a normochromic anemia with thrombocytosis and often reveals a normal leukocyte count.  There are certain subtle findings that may be seen on visualization of the peritoneum with ultrasound or CT scan that may be suggestive, but certainly not diagnostic for the disease.  It is essential that all patients with ascites and suspected TB have a diagnostic paracentesis.  The ascitic fluid will classically be straw colored with 500-1500 white blood cells per cubic millimeter, with a lymphocyte predominance.  Although the lymphocyte predominance is a key feature to help “clue in” on the diagnosis, it should be noted that it can be absent, especially in patients with coexisting renal disease, who often present with ascites with a neutrophil predominance.  The ascitic fluid should be exudative (serum albumin to ascites albumin gradient of <1.1 mg/dL), but again, there are exceptions, especially with coexisting cirrhosis.

The “AFB smear” of the ascites fluid, technically known as the Ziehl-Neelsen stain, has a frustratingly low sensitivity of 3%!  Thus, 97% of patients with TB peritonitis (with the gold standard defined as a positive peritoneal biopsy of caseating granulomas or a positive peritoneal culture performed via laparoscopy) will have a negative initial AFB smear.  The “AFB culture” of the ascites fluid performs better, with a sensitivity of 35%, but still many cases will be missed and the bacilli take weeks to grow in culture.  In our CRS case, the AFB culture was positive in the two paracenteses performed prior to starting treatment.  Apparently, if the necessary laboratory facilities are available, the sensitivity of the AFB culture increases to 66-83% if a large volume of ascites fluid (~1 liter) is extracted and then centrifuged.  The adenosine deaminase (ADA) test is a nice adjunct to AFB culture because results will likely come back sooner than culture.  ADA is an enzyme released from T lymphocytes, and at a cutoff level of 30 U/L of ascites fluid, has a sensitivity and specificity for TB peritonitis of >90%. 

Prognosis and Treatment

TB peritonitis is estimated to have an overall mortality of 19%, but this likely varies widely depending on patient characteristics as well as the availability of diagnostic testing and treatment.  Once the diagnosis is made, treatment is the same as for pulmonary tuberculosis, assuming it is not a resistant strain: RIPE (rifampicin, isoniazid, pyrizinamide, ethambutol) therapy, with an initiation phase of 2 months followed by maintenance therapy with RI, generally for 4 months.  Co-treatment with steroids has been proposed to reduce the inflammatory response, but this has not definitively shown to improve outcomes.  In patients with coexisting liver disease, it is important to be on the look out for signs of hepatoxicity, which is a common side effect of RIPE therapy. 

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Eliany Mejia,
Dec 16, 2013, 6:35 AM
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