Morbilliform rashes (Morbilli in Latin means “measles”) indicate an internal disorder and are not from external factors. The most common causes are viral and medications. A less common reason could be from a connective tissue disease. Other even rarer contributors to the morbilliform rash is serum sickness, rickettsial infections such as the dreaded Rocky Mountain spotted fever and a childhood virus called roseola vaccinatum. The majority of morbilliform eruptions don’t have a characteristic distribution, however, unilateral thoracic exanthems present on one side of the body and Rocky Mountain spotted fever tends to begin on hands and feet.
Obtaining a thorough history is important in these individuals and asking the right questions help guide towards appropriate diagnosis and treatment. Read on to view the most important questions to ask when faced with this kind of rash:
- How long have you had this rash? Viral and medicinal causes will present with acute eruptions in contrast to connective tissue diseases such as lupus erythematosus, which are more commonly chronic or recurrent.
- Are you taking any new medications? This question is helpful to know, especially if they’ve started a new medicine within the past 10 days. Oral antibiotics are the most frequent cause of morbilliform rashes.
- Do you have a recent history of a fever? Asking this question can verify an infectious cause.
- Do you have a history of any medical problems? Have they had a connective tissue disorder or a virus called mononucleosis? If a patient has been given ampicillin while having mononucleosis, a morbilliform rash may ensue.
- Do you have any lesions in your mouth? Oral lesions, while they may be present, are usually absent in drug reactions inducing a morbilliform rash. Some morbilliform rashes from viral causes may produce oral lesions, but not typically in rickettsial infections.
- Do you have any blisters? By definition, morbilliform rashes do not exhibit blisters. It is good to remember however that some blistering eruptions start out looking similar to a morbilliform rash. An example of this is erythema multiforme.
- Is hemorrhage present in any of the lesions? In morbilliform viral and drug eruptions, focal hemorrhage may occur especially on the lower extremities. Hemorrhage should raise the suspicion of Rocky Mountain spotted fever or early leukocytoclastic vasculitis.
- Is there a netlike appearance? A netlike or reticulated appearance of a morbilliform rash may raise the possibility of erythema infectiosum, however, this pattern may be seen in other morbilliform rashes.
Penicillin antibiotics are common culprits in causing morbilliform rashes as well as other medications such as allopurinol, phenytoin and sulfonamide antibiotics. Morbilliform medication reactions begin most commonly 3-10 days after the drug has been administered. An elevated eosinophil serum level favors a drug eruption and a very high eosinophil level may indicate a severe hypersensitivity reaction.
Discontinuing the offending drug is key to alleviating further progression. Occasionally some people have persisted in demonstrating progression of the rash even though the drug has been stopped. Symptomatic treatment measures are implemented. In the majority of cases, the rash will begin to subside in 1-3 days and completely resolve in 1-2 weeks.
Reference:
- Fitzpatrick JE, High WA. Morbilliform eruptions. Urgent Care Dermatology: Symptom-Based Diagnosis. Canada: Elsevier; 2018:31-34
