Differential Diagnosis for Measles-Like Rash Without Fever and Without URI Symptoms

Single Most Likely Diagnosis

• Kawasaki Disease: Although classically associated with fever, some cases of Kawasaki disease can present without fever, and the rash can mimic measles. The absence of URI symptoms and the presence of a measles-like rash make this a consideration, especially in children.

Other Likely Diagnoses

• Rubella (German Measles): While it often presents with mild symptoms including low-grade fever, it's possible for the fever to be absent or very mild, and the rash can be similar to measles.
• Roseola: Typically presents with a high fever followed by a rash, but in some cases, the fever might be mild or absent, and the rash could be mistaken for measles.
• Erythema Infectiosum (Fifth Disease): Characterized by a "slapped cheek" appearance and a lacy rash on the body, it can sometimes be mistaken for measles, especially if the slapped cheek appearance is not prominent.
• Allergic Reactions or Contact Dermatitis: Certain allergic reactions or contact dermatitis can cause rashes that might resemble measles, especially if they are widespread and not clearly related to a specific allergen or irritant.

Do Not Miss Diagnoses

• Meningococcemia: A life-threatening condition that can cause a rash, often accompanied by fever, but in early stages or in certain presentations, the fever might be absent. The rash can be petechial or purpuric but can sometimes be confused with measles in its early stages.
• Rocky Mountain Spotted Fever (RMSF): Although typically associated with fever and headache, the rash can sometimes be the presenting feature, and it's crucial to consider this diagnosis due to its severity and the need for prompt treatment.
• Syphilis (Secondary): Can cause a wide variety of rashes, including ones that might be mistaken for measles. Given the potential for serious complications if left untreated, it's a diagnosis that should not be missed.

Rare Diagnoses

• Mononucleosis: Caused by Epstein-Barr virus, it can occasionally present with a rash, which might be mistaken for measles, especially if the patient has not had a typical infectious mononucleosis syndrome.
• Enteroviral Infections: Certain enteroviruses can cause rashes that might resemble measles, though these are less common and often associated with other symptoms.
• Drug Reactions: Certain medications can cause rashes that might be confused with measles, especially if the patient is taking a new medication and the rash appears shortly after starting it.