What You Should Know about Tuberculosis for the Physician Assistant Exam
The Physician Assistant Exam (PANCE) will expect you to know that the causative organism of tuberculosis (TB) is Mycobacterium tuberculosis. It is transmitted from person to person, usually by respiratory droplets.
Initial symptoms of TB can show a cough that gets progressively worse. There can also be type B constitutional symptoms. Hemoptysis may or may not be present.
Types of TB
There are several types of tuberculosis and several disseminations. The World Health Organization estimates that about a third of the world’s population is infected with M. tuberculosis.
Primary tuberculosis concerns initial exposure to the mycobacterium, which triggers an inflammatory reaction in the lungs. Chest radiograph findings can show hilar adenopathy and nonspecific infiltrates; however, they don’t always show up on a chest radiograph.
A Ghon nodule is simply a tuberculous lesion that has healed. It looks small and calcified on a chest radiograph.
For someone who has a problem with the immune system, primary tuberculosis in the lung can spread. In primary progressive tuberculosis, the TB can spread via the lymphatics, and the lung disease worsens. It can spread into the pleura and cause a pleural effusion. The mycobacterium can also spread in the blood (through hematogenous dissemination) to other body organs, leading to extrapulmonary TB.
Tuberculosis can reactivate. Some latent infection is usually somewhere in the body. The most common place for reactivation is in the upper lobes of the lung, specifically the apical and posterior regions. This can be a cavitary pneumonia.
Miliary tuberculosis is tuberculosis that has disseminated throughout the body. It can affect any organ, and it occurs less than 5 percent of the time. Classic chest radiograph findings make it look like someone took a machine gun and shot out the lungs. These bullet-like small nodules appear throughout both lung fields.
TB skin tests
At some point, everyone who has applied for a job in healthcare has undergone skin testing for tuberculosis. What’s a positive test? The size of the wheal, not the redness, is what matters. But interpreting whether someone’s positive means not only looking at the size of the wheal or induration but also paying attention to the risk factors. Here are key points you need to know:
If the wheal is > 5 mm, the following groups are considered to be positive for TB: people with HIV, those who have been in contact with someone who has active TB, and those who are on chronic immunosuppressive therapy, such as prednisone and anti-rejection medications (cyclosporine [Neoral] and tacrolimus [Prograf]).
If the wheal is > 10 mm, these groups are considered to be positive: people who are active drug users, healthcare personnel, and other employees and residents of high-risk areas, including nursing homes, residential care facilities, and jails. Other risks include chronic medical conditions that can render people immunosuppressed, including diabetes, advanced kidney disease, and COPD. People who’ve emigrated to this country from endemic areas fall into this category.
Any individual who has a wheal > 15 mm is considered positive and has risk factors for developing tuberculosis.
How to treat TB
Different therapies and drug regimens can be used to treat TB. Many of them can last 6 to 9 months. For PANCE purposes, you should be familiar with side effects of the medications:
Isoniazid (INH), which is usually the first-line treatment, can cause a peripheral neuropathy. It may also cause low levels of vitamin B6, so supplementation with vitamin B6 is recommended. Because isoniazid carries a risk of hepatitis, liver function tests need to be monitored while the person is on the medication.
Rifampin can turn the urine and secretions a funky orange color. Rifampin is a potent enzyme inducer that can affect the metabolism of many drug classes, including HIV meds. It has gastrointestinal effects, can cause thrombocytopenia, and can be toxic to the liver.
Pyrazinamide can cause some minor joint pains, but the main effect is liver toxicity. It can raise serum uric acid levels.
Ethambutol’s significant side effect concerns the eye. It can cause color blindness, and in some studies, it caused optic neuropathy.