Differential Diagnosis for Skin Rash
The patient presents with a skin rash that started as a blister on the finger, then spread to different parts of the body, accompanied by extreme itching and pain. Here's a differential diagnosis organized into categories:
- Single Most Likely Diagnosis
- Contact Dermatitis: This is a common condition that can start with a blister and spread, especially if the causative agent (like a plant allergen) comes into contact with other parts of the body. The extreme itching and pain are consistent with an allergic reaction.
- Other Likely Diagnoses
- Eczema (Atopic Dermatitis): Characterized by itchy, inflamed skin, and can start with a localized lesion that spreads. The blister could be a manifestation of a flare-up.
- Psoriasis: Although less common to start as a blister, psoriasis can cause painful, itchy lesions that spread across the body.
- Herpes Zoster (Shingles): Typically starts with a painful rash that can blister, usually confined to one side of the body but can spread. The pain is often severe.
- Do Not Miss Diagnoses
- Stevens-Johnson Syndrome (SJS) / Toxic Epidermal Necrolysis (TEN): These are life-threatening conditions usually triggered by medications or infections. They can start with blistering lesions and spread, accompanied by severe pain and systemic symptoms.
- Pemphigus Vulgaris: An autoimmune disease that causes blistering of the skin and mucous membranes. It can be painful and itchy, and if not treated, can be fatal.
- Rare Diagnoses
- Bullous Pemphigoid: An autoimmune disease that causes blistering skin lesions. It's less common and usually affects older adults, but it can cause significant discomfort and morbidity.
- Dermatitis Herpetiformis: A skin manifestation of celiac disease, characterized by itchy, blistering skin. It's rare but important to diagnose due to its association with celiac disease.
Each of these diagnoses has the potential to explain the patient's symptoms, but the likelihood varies based on the presentation and epidemiology. A thorough history, physical examination, and diagnostic tests (such as skin biopsy, patch testing, or blood tests) are necessary to determine the exact cause of the rash.