Differential Diagnosis for Viral Rash in 1-year-old Boy

Single Most Likely Diagnosis

• Roseola (Exanthem Subitum): A common viral illness in children, characterized by a high fever followed by a maculopapular rash that starts on the trunk and spreads to other parts of the body. The age of the patient and the description of the rash make this a likely diagnosis.

Other Likely Diagnoses

• Enterovirus: Enteroviruses can cause a variety of rashes, including maculopapular rashes, and are common in children. The presence of a low-grade fever and the rash's progression from feet to chest could be consistent with an enteroviral infection.
• Erythema Infectiosum (Fifth Disease): Although it typically starts with a "slapped cheek" appearance, the rash can spread to the body and have a maculopapular appearance. However, the lack of the characteristic facial rash might make this less likely.
• Measles: Although less common due to vaccination, measles can present with a maculopapular rash that starts on the face and descends. The presence of fever and the rash's progression could fit, but the vaccination status of the child would be a critical factor.

Do Not Miss Diagnoses

• Kawasaki Disease: A serious condition that can present with fever, rash, and other symptoms. It's crucial to consider this diagnosis due to its potential for causing coronary artery aneurysms if not treated promptly.
• Meningococcemia: Although the rash is typically petechial or purpuric, early stages can be maculopapular. Given the potential severity of this condition, it's essential to consider it, especially if there are other signs of severe illness.
• Rocky Mountain Spotted Fever (RMSF): This tick-borne illness can present with a maculopapular rash that starts on the wrists and ankles and spreads to the trunk. Given the location (Maryland), RMSF is a possibility, especially during warmer months.

Rare Diagnoses

• Scarlet Fever: Characterized by a sandpapery rash that typically follows a sore throat, it's less common due to antibiotic treatment of streptococcal infections but should be considered if there are other suggestive symptoms.
• Dengue Fever: Although less likely in Maryland without recent travel history, dengue can cause a maculopapular rash along with fever and other systemic symptoms.
• Zika Virus: Similar to dengue, Zika virus infection would be unusual without travel history but could present with a maculopapular rash among other symptoms.