Differential Diagnosis for Pruritic Rash
- Single most likely diagnosis
- Contact dermatitis: This is the most likely diagnosis given the initial localized rash on the inner left arm, which then spread to other areas. The rash's progression and pruritic nature are consistent with an allergic reaction to a substance that came into contact with the skin.
- Other Likely diagnoses
- Atopic dermatitis (eczema): The pruritic nature of the rash and its spread to multiple areas, including the groin and behind the knees, are consistent with atopic dermatitis, especially if the patient has a history of allergies or asthma.
- Scabies: The intense pruritus and spread of the rash to multiple areas, including the groin, suggest scabies, particularly if the patient has had close contact with someone infected.
- Insect bites: The rash's appearance and pruritic nature could be due to insect bites, especially if the patient has been outdoors or in an area with high insect activity.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Stevens-Johnson syndrome: Although rare, this life-threatening condition can present with a rash and pruritus, and it is essential to consider it to avoid missing a potentially fatal diagnosis.
- Toxic epidermal necrolysis: Similar to Stevens-Johnson syndrome, toxic epidermal necrolysis is a severe condition that requires prompt recognition and treatment to prevent significant morbidity and mortality.
- Rare diagnoses
- Pityriasis rosea: This condition can cause a pruritic rash that spreads to multiple areas, but it typically starts with a herald patch and has a distinctive appearance.
- Dermatitis herpetiformis: This rare skin condition is characterized by a pruritic, blistering rash, often on the elbows, knees, and buttocks, and is associated with celiac disease.
- Erythema multiforme: This condition can cause a rash with target lesions, often accompanied by pruritus, and can be triggered by infections or medications.