A man has recurrent uicaria following exercise and coming out in sun. Diagnosis is:
**Core Concept**
Urticaria is a common skin condition characterized by the sudden appearance of itchy, raised welts (hives) on the skin. In this case, the patient's symptoms are triggered by exercise and exposure to sunlight, suggesting a specific underlying mechanism.
**Why the Correct Answer is Right**
The patient's symptoms are consistent with solar urticaria, a rare form of physical urticaria triggered by exposure to sunlight. This condition is thought to be caused by the release of histamine from mast cells, which are activated by the ultraviolet radiation from the sun. The exact mechanism is not fully understood, but it is believed to involve the formation of cyclobutane pyrimidine dimers (CPDs) in skin cells, leading to the activation of mast cells and the release of histamine. This results in the characteristic symptoms of urticaria, including itching, redness, and swelling.
**Why Each Wrong Option is Incorrect**
**Option A:** This is not a specific diagnosis, and the symptoms described do not fit with a diagnosis of angioedema, which is a different condition characterized by the rapid swelling of the skin and mucous membranes.
**Option B:** Cholinergic urticaria is a form of physical urticaria triggered by heat, exercise, or emotional stress, but it is not typically triggered by sunlight alone.
**Option C:** Cold urticaria is a form of physical urticaria triggered by exposure to cold temperatures, which is not consistent with the patient's symptoms.
**Clinical Pearl / High-Yield Fact**
Solar urticaria can be challenging to diagnose, but it is often associated with a history of skin cancer or other skin conditions, and patients may experience worsening symptoms over time.
**Correct Answer: D. Solar urticaria. Solar urticaria is a rare form of physical urticaria triggered by exposure to sunlight.