Differential Diagnosis for Maculopapular Itchy Rash
Single Most Likely Diagnosis
- Atopic Dermatitis (Eczema): This is a common condition characterized by itchy, inflamed skin that can appear anywhere on the body, including the arms and neck. The chronic nature of the rash (over 7 days) and its itchy nature align with atopic dermatitis.
Other Likely Diagnoses
- Contact Dermatitis: An allergic reaction or irritation from substances like soaps, detergents, or metals can cause a maculopapular itchy rash. Given the location on arms and neck, exposure to allergens or irritants in these areas is plausible.
- Allergic Reaction to Medication: Certain medications can cause skin reactions, including maculopapular rashes. The timing and distribution of the rash could suggest a drug allergy, especially if the patient has recently started new medications.
- Insect Bites: Repeated bites from insects like mosquitoes or bed bugs can cause itchy maculopapular rashes, particularly on exposed areas like the arms and neck.
Do Not Miss Diagnoses
- Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN): Although rare, these conditions are life-threatening and can initially present with a maculopapular rash that progresses to blistering and peeling of the skin. They are often drug-induced and require immediate medical attention.
- Syphilis (Secondary): This sexually transmitted infection can cause a variety of skin rashes, including maculopapular types, and is crucial to diagnose due to its implications for public health and the potential for serious complications if left untreated.
Rare Diagnoses
- Pityriasis Rosea: Characterized by a herald patch followed by a widespread, symmetrical, maculopapular rash, this condition is relatively rare and its cause is unknown. It typically resolves on its own within a few weeks.
- Kawasaki Disease: An acute febrile illness that predominantly affects children, characterized by fever, rash, swelling of hands and feet, conjunctivitis, and cervical lymphadenopathy. The rash can be maculopapular and is a critical diagnosis to consider due to the risk of cardiac complications.
- Drug-Induced Lupus: A rare condition triggered by certain medications, leading to symptoms that can include a maculopapular rash, among other systemic manifestations.