From the Guidelines
Morbiliform rashes are typically caused by viral infections, drug reactions, and certain autoimmune conditions, with the most recent and highest quality evidence suggesting that common viral causes include measles, rubella, parvovirus B19, Epstein-Barr virus, and enteroviruses, as well as drug-induced reactions, particularly from antibiotics and anticonvulsants 1.
Causes of Morbiliform Rashes
The causes of morbiliform rashes can be categorized into several groups, including:
- Viral infections: such as measles, rubella, parvovirus B19, Epstein-Barr virus, and enteroviruses
- Drug reactions: particularly from antibiotics (e.g., penicillins, cephalosporins, and sulfonamides), anticonvulsants (e.g., phenytoin and carbamazepine), and allopurinol
- Autoimmune conditions: such as Still's disease and Kawasaki disease
Characteristic Appearance
The characteristic appearance of morbiliform rashes includes:
- Flat, red macules and papules that may coalesce
- Localized inflammation and vasodilation in the skin due to immune system activation against the triggering agent
Evaluation and Treatment
When evaluating a morbiliform rash, it's essential to consider:
- Recent medication changes
- Viral symptoms
- Associated findings like fever, lymphadenopathy, or mucosal involvement Treatment depends on identifying and addressing the specific cause, which may involve:
- Discontinuing an offending medication
- Treating the underlying infection or condition As noted in a recent study, a single-dose amoxicillin challenge without prior allergy testing is recommended for pediatric patients with a history of benign cutaneous reaction, such as morbiliform rash, to determine if they are truly allergic to the medication 1.
From the Research
Causes of Morbilliform Rash
The causes of a morbilliform (maculopapular) rash can be attributed to various factors, including:
- Viral infections, such as measles 2, rubella 3, parvovirus B19 4, human herpesvirus type 6 4, enterovirus 4, and adenovirus 4
- Bacterial infections, such as group A streptococcus 4 and group C streptococcus 4
Viral Infections
Viral infections are a common cause of morbilliform rash, with measles and rubella being two examples:
- Measles is a highly contagious disease that typically begins with fever, runny nose, cough, and a characteristic erythematous, maculopapular rash 2
- Rubella, also known as German measles, is usually a mild infection that can cause a scarletiniform rash, cervical lymphadenopathy, and mild constitutional symptoms 3
Bacterial Infections
Bacterial infections can also cause morbilliform rash, including:
- Group A streptococcus, which can cause a range of symptoms including rash, fever, and sore throat 4
- Group C streptococcus, which can also cause rash, fever, and other symptoms 4
Other Causes
Other causes of morbilliform rash include: