Differential Diagnosis
- Single most likely diagnosis
- Contact dermatitis: The patient was working outside in ragweed, which is a common allergen that can cause an allergic contact dermatitis. The rash started on the left arm and spread to the right arm and chest, consistent with exposure to an allergen.
- Other Likely diagnoses
- Allergic reaction to insect bite or sting: The patient was working outside, increasing the likelihood of an insect bite or sting, which can cause a red, raised rash.
- Irritant contact dermatitis: Exposure to plants, dirt, or other substances while working outside can cause an irritant contact dermatitis.
- Phytophotodermatitis: This is a skin reaction caused by exposure to certain plants, such as ragweed, and sunlight, which can cause a red, raised rash.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Anaphylaxis: Although the patient denies shortness of breath, wheezing, or throat closing, anaphylaxis can present with skin symptoms only, and it is essential to consider this diagnosis due to its potential severity.
- Stevens-Johnson syndrome: This is a rare but life-threatening condition that can be caused by an allergic reaction to certain substances, including plants.
- Rare diagnoses
- Photosensitivity reaction: This is a rare condition where the skin reacts to sunlight, causing a red, raised rash.
- Plant-induced urticaria: This is a rare condition where exposure to certain plants causes hives or a red, raised rash.