look for metaphyseal lytic lesions with little or no sclerosis, and no periosteal reaction;
juxta-articular / joint involvement
hips and knees are affected most frequently;
may present as gradually worsening arthritis but is often mistaken for some other form of arthritis (such as "mono-articular rheumatoid arthritis" or PVNS);
peri-articular osteopenia is common;
unlike most forms of arthritis, TB joint involvement is most often mono-articular;
note that in TB arthropathy, the joint space will often be maintained (unlike RA);
phalangeal tuberculous osteitis:
look for soft tissue swelling, cortical thinning, medullary destruction, and periosteal
reaction involving the middle and distal phalanx;
in the past, when strict prevention measures were not manditory, there have been some reports of nearly half of health care
students becoming PPD positive after 1 year;
patients known or suspected to be infected need to wear a HEPA mask and need to be placed in respiratory isolation;
respiratory isolation should include a room w/ special ventilation, optimally with HEPA filters;
elective surgery on actively infected patients should be delayed until the disease is treated and enters a latent phase;
Skin Testing
in the U.S. about 10-15% of the population will have positive test;
patients who have been given the bacille Calmette Guerin vaccine will have positive tests;
w/ infection, skin tests are usually, but not always, positive;
false negative tests will occur in malnourished patients and AIDS patients;
skin testing in a patient w/ an active infection may result in skin slough;
Laboratory Diagnosis
bacterium is a thin rod w/ rounded ends;
classic histologic pattern reveals central necrotic area surrounded by histiocytes and occasional giant cells with nuclei
positioned at the margin of the cell;
Ziehl-Neelsen Staining Method
note potential false negative results are a frequent occurance;
tuberculum is acid fast (resist decolorization w/ acids)
requires use of enriched medium and adequate oxygenation;
cultures visible at 2-4 weeks;
note that joint aspiration may not produce positive culture, and w/ suspected joint infection, a synovial biopsy may be required;
Medical Treatment of Tuberculosis Infection
preventive therapy
preventive therapy with insoniazid given for 6-12 months is effective in decreasing the risk of future tuberculosis;
persons for whom preventitive therapy is indicated include: household members and other close contacts of potentially
infectious persons;
newly infected persons; persons with past tuberculosis or with a significant tuberculin reaction and abnormal chest films in whom current TB has been excluded;
infected persons in special clinical situations such as sillicosis, diabetes mellitus, adrenocorticosteroid therapy;
persons at high risk of developing severe forms of tuberculosis, if infected due to contact w/ a person having INH resistant
organisms, should be treated with rifampin rather than INH;
acute infection
isoniazid, rifampin, and pyrazinamide (20-25 mg / kg / day) given for 2 months, after which time isoniazid and rifampin for 4 months is effective treatment in patients with fully susceptible organisms who comply with the treatment regimen;
9 month regimen consisting of isoniazid and rifampin is also highly successful;
need for additional drug in initial phase is not certain unless isoniazid resistance is suspected;
w/ suspected INH resistance, consider the addition of ethambutol in initial phase;
children should be treated in essentially the same way as adults using appropriately adjusted doses of the drugs;
dormant infection
rifampin (10 mg/kg/day) and pyrazinamide are most effective
