WBR0452
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pharmacology |
| Sub Category | SubCategory::Gastrointestinal |
| Prompt | [[Prompt::A 24 year old male patient presents to the physician’s office with watery diarrhea of several days duration. Following appropriate work-up, the patient undergoes intestinal biopsy that reveals transmural inflammatory infiltration with granulomatous skip lesions. The patient is then diagnosed with Crohn’s disease. The physician wishes to prescribe infliximab. Which of the following tests must be performed before the initiation of infliximab therapy?]] |
| Answer A | AnswerA::CD4 count |
| Answer A Explanation | AnswerAExp::CD4 count is important for HIV patients. It is however not pertinent before initiation of anti-TNF therapy. |
| Answer B | AnswerB::HBsAg |
| Answer B Explanation | AnswerBExp::HBsAg is diagnostic of hepatitis B virus (HBV). HBV screening is not needed before initiation of anti-TNF therapy. |
| Answer C | AnswerC::HCV RNA |
| Answer C Explanation | AnswerCExp::HCV RNA is diagnostic of hepatitis C virus (HCV). HCV screening is not needed before initiation of anti-TNF therapy. |
| Answer D | AnswerD::Monospot test |
| Answer D Explanation | [[AnswerDExp::Monospot test is a helpful test for Epstein-Barr virus (EBV). However, monospot test is not specific and can be positive in other infections and in hematologic malignancies as well. EBV screening is not needed before initiation of anti-TNF therapy.]] |
| Answer E | AnswerE::Mendel-Mantoux test (PPD test) |
| Answer E Explanation | [[AnswerEExp::PPD test or Mendel-Mantoux test is helpful in the diagnosis of latent tuberculosis in a healthy individual. However, PPD test can also be positive in individuals who have received the Bacillus Calmette-Guerin (BCG) vaccine. Screening for tuberculosis is necessary before initiation of anti-TNF therapy.]] |
| Right Answer | RightAnswer::E |
| Explanation | [[Explanation::Infliximab is a anti-tumor necrosis factor (TNF) monoclonal antibody that inhibits its activity. Infliximab and other TNF inhibitors are effective for treatment of Crohn’s disease. A potential adverse event of anti-TNF use is the reactivation of latent tuberculosis. Hence, PPD test before the initiation of anti-TNF therapy is necessary.
TNF, expressed by macrophages and T cells, is integral for the development of granulomas that can limit the reactivation of tuberculosis in immunocompetent patients. Patients who are on anti-TNF therapy will lose the ability to form granulomas, leading to tuberculous reactivation. PPD test or Mendel-Mantoux test is a helpful test in diagnosing latent tuberculosis in individuals who have no signs of active infection. PPD positivity, however, can also be seen in patients who have received Bacillus Calmette-Guerin (BCG) vaccine. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Tuberculosis, WBRKeyword::PPD, WBRKeyword::Mendel-mantoux, WBRKeyword::Infiximab, WBRKeyword::Crohn disease, WBRKeyword::Granuloma, WBRKeyword::Crohn's disease, WBRKeyword::TNF, WBRKeyword::TNF-alpha |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |