Differential Diagnosis
- Single most likely diagnosis
- Contact dermatitis: This is the most likely diagnosis given the patient's recent camping trip and exposure to potential allergens or irritants in the environment, such as plants or insects. The presence of excoriated papulovesicular lesions over the forearms and legs also supports this diagnosis.
- Other Likely diagnoses
- IgE-mediated hypersensitivity: The patient's intensely itchy rash and the fact that several other boys in his camping party have a similar rash suggest an allergic reaction, which could be mediated by IgE. The recent introduction of a kitten to the family could also be a potential allergen.
- Scabies: The itchy, blistering rash and the fact that several other boys in the camping party have a similar rash could suggest scabies, a highly contagious skin infestation caused by the mite Sarcoptes scabiei.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Eczema herpeticum: Although less likely, eczema herpeticum is a serious condition that can occur in patients with a history of eczema, characterized by a disseminated herpes simplex virus infection. It requires prompt recognition and treatment to prevent serious complications.
- Rare diagnoses
- Drug eruption: Although the patient is taking phenytoin, which can cause skin reactions, the timing and description of the rash make this a less likely diagnosis. However, it should still be considered, especially if the patient has recently started or changed his medication.
- Other rare diagnoses, such as allergic contact dermatitis to specific substances (e.g., poison ivy, oak, or sumac) or insect bites, could also be considered, but are less likely given the information provided.