Differential Diagnosis for the 71-year-old Female Patient
- Single most likely diagnosis
- Contact dermatitis: This is the most likely diagnosis given the patient's history of gardening and the onset of the rash after exposure to potential allergens or irritants in the garden. The fact that the rash is extremely itchy and has spread to various parts of the body also supports this diagnosis.
- Other Likely diagnoses
- Allergic reaction to plants (e.g., poison ivy, oak, or sumac): The patient's gardening activity increases the risk of exposure to these plants, which can cause an allergic reaction resulting in a rash.
- Eczema (atopic dermatitis): Although the patient denies any change in soaps or creams, eczema can be triggered by various factors, including environmental allergens.
- Insect bites or stings: The patient's outdoor activity could have exposed her to insects, which might have caused the itchy rash.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Cellulitis: Although less likely, cellulitis is a serious bacterial infection that can cause a rash and should not be missed. It requires prompt antibiotic treatment to prevent serious complications.
- Erythema multiforme: This is a rare but potentially life-threatening condition that can cause a rash and is often triggered by infections or medications.
- Rare diagnoses
- Phototoxicity: This is a rare condition caused by a reaction to certain medications or substances that can cause a rash after sun exposure.
- Autoimmune disorders (e.g., pemphigus, pemphigoid): These are rare conditions that can cause blistering rashes, but they are less likely given the patient's presentation and history.