Q 34.  A 78 year old man comes to the office because he volunteers at the local hospital and is required to get a tuberculin skin test annually.  A tuberculosis skin test (PPD) using 5 tuberculin units was done a year ago when he first started.  At that time, the test was read as 4 mm induration and interpreted as negative.  On retesting now a year later, there is 16 mm of induration.  He has no symptoms, and chest radiograph is negative.  He is on coumadin for atrial fibrillation but has no other problems and no other medications.

What is the most appropriate next step in management?

A.  Observation only

B.  Annual chest radiography

C.  Repeat PPD testing in 6 months

D.  Treatment with pyrazinamide plus rifampin for 2 months

E.  Treatment with INH for 9 months

Answer: E

"The patient is a recent converter (induration enlarged from <10 to >15 within 2 years);  However it is possible that he has undergone a "booster" response in which the first PPD done a year ago "boosted" his T cell memory so that a second PPD resulted in a greater reaction.  This is why two step testing has been recommended for new long term care residents and staff and for all healthcare personnel.  In either case, a positive test warrants therapy (regardless of age).  All patients with a positive PPD should have active disease excluded by a thorough examination and chest radiograph;  if this evaluation is negative, 9 months of INH is the appropriate treatment.  This is true despite the drug interaction with warfarin.  In this case, he also would qualify for INH therapy based only on the size of the PPD reaction (> 15 mm) which is always considered positive regardless of other factors, including age, underlying illness, prior administration of BCG vaccine, etc.  In those with specific specific risk factors, which are quite common in older adults (diabetes, gastrectomy/achlorhydria, excessive weight loss, chronic renal disease, etc), a PPD >10 mm of induration is considered positive.  In immunocompromised patients, in those with changes on chest radiographs typical of prior TB, and in those recently exposed to someone with active disease, a PPD > 5 mm is considered positive.

This patient has a 10% risk of developing active TB within 2 years and works in a healthcare setting; thus, observation and chest radiography are not indicated.  Repeat PPD testing will not change management options and is not needed.  Treatment with pyrazinamide and rifampin has been shown to be effective in treating latent TB in patients with HIV but is considered second line to 9 months of INH treatment. "

Take home pearl:  decision to treat latent TB is not based upon age