Internal organ involvement in drug hypersensitivity skin reactions

Mohannad Abu-Hilal, MD, is an associate professor of Medicine and head and of the Dermatology Division at McMaster University.

When to expect internal organ involvement in patients with a cutaneous drug hypersensitivity reaction? What tests could be useful?

It’s very hard to just expect them. You should always be vigilant and look for some internal manifestations, but there is nothing that we can do to [predict] if the patient is going to have internal manifestations or not. Remember, a lot of those reactions could just look similar, whether [they are] mild or severe. Always look for them and investigate and evaluate for those internal manifestations.

Now, the test that you need to be doing... Definitely you need to do a complete blood count (CBC) with differential and should look for the platelet counts and the atypical lymphocytes. Those tests might show some cytopenia, low blood count—low white or red blood cell count. Sometimes you can see elevation in the platelet counts or low platelet counts. In the blood smear you can sometimes see atypical lymphocytes. Definitely you can see a lot of eosinophilia, which is elevated eosinophil counts, in those reactions.

Definitely we should be looking [at] and doing some liver function tests, namely the alanine aminotransferase (ALT) and the aspartate aminotransferase (AST) enzymes. Those could be elevated, especially in the drug reaction with eosinophilia and systemic symptoms (DRESS), where the AST/ALT will be elevated. Also, we should do kidney function tests because some of those severe reactions can cause acute renal failure. You want to make sure that the patient is not dealing with renal failure.

Other test that we should also be doing is urinalysis. Some of those reactions like DRESS can cause nephritis where you could be seeing some protein or sometimes some eosinophils in the urinalysis. Some other tests that you need to be running are, for example, based on the symptoms—if the patient is complaining, for example, about a kind of muscle pain, you might need to think about the patient having myocarditis and you might take the creatine kinase (CK) enzyme; if the patient is having, for example, some chest pain, which is a rare complication of some of the severe reactions, you might need to do some troponin and check for cardiac enzymes.

Again, the basic ones, the common ones, are the CBC, the blood smear, the liver function, the kidney function, and urinalysis.