HIV Basics for the Physician Assistant Exam
For the Physician Assistant Exam (PANCE), you should be familiar with some general stuff concerning HIV, specific infections related to HIV, and side effects of certain medications. HIV stands for human immunodeficiency virus. Risk factors for acquiring HIV include high-risk sexual behavior and drug abuse, especially intravenous use with dirty needles. Coming into contact with contaminated blood from someone with HIV is also a cause.
Almost right after someone is infected, he or she may experience an acute syndrome related to the HIV infection. It can cause typical flu-like symptoms, with gastrointestinal upset, sore throat, fever, muscle aches, and joint pains. You may also see neuropathy and a skin rash.
Testing for HIV includes an initial enzyme-linked immunosorbent assay (ELISA), followed by the confirmatory western blot. The big issue with HIV is establishing how well the immune system is functioning, which you do by ordering a CD4 count and a plasma HIV RNA level.
The lower the CD4 count, the higher the risk of acquiring certain infections. HIV also involves an acquired deficiency of T cells, which are important for conferring cellular immunity.
The treatment, which is a science in and of itself, has transformed the lives of millions of people. It involves using different categories of medications, including protease inhibitors, reverse transcriptase inhibitors, and others. Here are four high-yield items about HIV meds you should know for the test:
Zidovudine (AZT) causes a macrocytic anemia. You can see a mean corpuscular volume (MCV) > 100 in someone on this medication. Folate replacement may be needed.
Didanosine (DDI, brand name Videx) causes pancreatitis.
Tenofovir disoproxil fumarate (TDF, brand name Viread) causes acute kidney failure.
Indinavir (Crixivan) causes kidney stones.
Some PANCE questions concern infections, especially at the lower CD4 counts. These infections include toxoplasmosis and atypical mycobacterial infections. They’re rampant in the HIV population, and the majority of test questions about infections are likely to involve underlying HIV. Here are some key points related to infections:
A normal CD4 count is >= 500 cells. The risk for many opportunistic infections occurs when the CD4 count falls below 250. A CD4 count of < 200 is considered diagnostic for AIDS.
Remember the four c’s, which you can see in advanced HIV: Candida, Cryptococcus, Cryptosporidium, and CMV (cytomegalovirus). Cryptosporidium is a cause of infectious diarrhea in someone with advanced HIV.
Toxoplasmosis is caused by a parasite. Cats are actually the ones primarily infected, because Toxoplasma gondii shows up in their feces. In someone with HIV, the infections are potentially fatal. This parasite can cause encephalitis. On a CT scan of the head with contrast, toxoplasmosis has been described as a “ring-enhancing lesion.” The treatment for toxoplasmosis is a combination of pyrimethamine and sulfadiazine.
In someone with a low CD4 count, trimethoprim/sulfamethoxazole (Bactrim) is used for pneumocystis and toxoplasmosis prophylaxis.
Tuberculosis and atypical mycobacterial disease are more prevalent in the HIV population. Concerning atypical mycobacterial infections, the big one to be familiar with is the Mycobacterium avium complex. You can see this infection in advanced HIV, with CD4 counts < 50. The most glaring presenting symptom of a MAC attack is significant adenopathy. It can cause gastrointestinal problems, including ulcers and diarrhea. It can also cause joint and muscle infections.
Treatments can include macrolide antibiotics, rifabutin, and the fluoroquinolones. Rifabutin and clarithromycin (Biaxin) seem to be the more popular meds asked about in test questions.