RESEARCH - PPD not enough to identify latent TB in many patients

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PPD not enough to identify latent TB in many patients

Rheumawire

Oct 19, 2004

Janis

San , TX - Clinicians have been advised to screen patients for

latent tuberculosis (TB) infection before initiating treatment with TNF

inhibitors or other immunosuppressive agents. Data reported by Mexican

researchers in 2 poster presentations at the American College of

Rheumatology 2004 meeting suggest that the usual screening combinations

of chest x-ray plus proteinic purified derivative (PPD) or tuberculin

skin test (TST) are not adequate for detecting asymptomatic TB in

patients from countries where there is a high prevalence of TB or where

bacillus Calmette-Guerin (BCG) vaccine is widely used.

Dr Francisco Medina (Centro Medico Nacional Siglo XXI, Mexico), who

worked on both studies, tells rheumawire that these concerns apply not

only to residents of countries like Mexico but also to arthritis

patients who emigrated from such areas. " TST is not a suitable test to

identify active or latent TB in patients with rheumatoid arthritis [RA]

or systemic lupus erythematosus [sLE]. Chest radiography sensitivity is

too low to justify the expense and the radiation exposure. I prefer to

test the adenosine deaminase [ADA] levels in plasma or serum, or even

better the M tuberculosis polymerase chain reaction [PCR] with either

computed tomography [CT] or magnetic resonance imaging [MRI], " he says.

Medina and colleagues described the characteristics of 11 patients with

autoimmune diseases and concomitant mycobacterial infection [1]. These

included 5 with SLE, 5 with RA, and 1 with reactive arthritis. Of the RA

patients, 1 was taking infliximab and 1 was taking etanercept. Medina

reported that all the patients denied having had active TB, and all had

received BCG vaccination.

" TST reactivity was: >15 mm in 3 cases, 10 to 14 mm in 3 cases, and <9

mm in 4 cases. Chest x-rays showed nondiagnostic findings in 4 patients

and were normal in 6 cases, " Medina said. Nine of the isolates were M

tuberculosis; 1 was M kansasii.

In related work, this team assessed the prevalence of skin reactivity to

tuberculin in patients with RA or SLE [2]. Dr Victor (Centro

Medico Nacional) tells rheumawire that PPD was positive in one third of

control adult subjects and in <20% of RA and SLE patients. A second PPD

test was positive in only 10% more patients.

" In a BCG-positive population like Mexico, 'classic' PPD is not a

suitable test to identify active or latent TB in RA and SLE, and testing

should be adjusted, as occurs in HIV infection and neoplasia, "

said.

This study included 165 consecutive patients with RA and 112 with SLE.

All patients were asked about BCG vaccination and about contact with TB

patients. Physical examination included a search for " epidemiologic

scar " on shoulders. Tests included chest x-rays and the Mantoux test. In

negative cases, a second PPD dose was done 1 to 4 weeks later. There

were 199 BCG-immunized healthy subjects used as controls.

reported that 90% of RA patients and 88% of SLE patients were

positive for BCG. Of the subjects, 19% of the RA patients, 13% of the

SLE patients, and 33% of the healthy subjects were PPD positive (p< 0.01

for both diseases). The second PPD test brought the total positive to

27% of RA patients, 21% of SLE patients, and 36% of controls. PPD

reactivity was not affected by disease activity or by use of

immunosuppressants.

" One third of the world population is infected with tuberculosis. Twenty

thousand people contract active TB every day and 5000 die for that

reason, " Medina said. " The prevalence of TB in patients with RA and SLE

has increased, mainly due to reactivation of latent infection. Because

of that, the CDC recommends screening with TST or PPD and chest

radiography. Although in countries that practice official immunization

against TB with BCG, such as Mexico, the meaning of a positive PPD test

is unclear, there is a prevalent view that BCG application converts

individuals to PPD positive. "

He advises clinicians in such countries and those treating emigrants

from such countries to ask about prior exposure to people with active TB

and prior vaccination with BCG and to consider a workup that includes

ADA or M tuberculosis PCR to rule out asymptomatic tuberculosis before

initiating TNF-inhibitor or other immune-suppressing therapy.

Sources

1. Medina F, V, Fuentes J, et al. Is there a role

for PPD and chest radiography in identification of asymptomatic

tuberculosis in rheumatic diseases? American College of Rheumatology

2004 meeting; October 16-21, 2004; San , TX; Abstract 185.

2. V, Chavez N, Carranza I, et al. Prevalence of

skin reactivity to tuberculin in patients with rheumatoid arthritis (RA)

and systemic lupus erythematosus (SLE). American College of Rheumatology

2004 meeting; October 16-21, 2004; San , TX; Abstract 197.

I'll tell you where to go!

Mayo Clinic in Rochester

http://www.mayoclinic.org/rochester

s Hopkins Medicine

http://www.hopkinsmedicine.org