A 45 year old farmer has itchy erythematous papular lesions on face, neck, ‘V’ area of chest, dorsum of hands and forearms for 3 years. The lesions are more severe in summers and improve by 75% in winters. The most appropriate test to diagnose the condition would be –
**Core Concept**
The farmer presents with characteristic skin lesions that worsen in the summer months and improve in the winter, suggesting a condition related to sunlight exposure. This pattern is typical of a photodermatosis, specifically a condition that involves an abnormal response to ultraviolet (UV) radiation.
**Why the Correct Answer is Right**
The condition described is likely solar dermatitis, also known as polymorphic light eruption (PMLE). PMLE is a common photodermatosis characterized by itchy erythematous papules that appear after exposure to UV radiation, particularly in the summer months. The lesions typically improve or resolve during the winter months when UV radiation is less intense. The condition is thought to be mediated by an abnormal immune response to UV-damaged skin cells, which triggers an inflammatory reaction.
**Why Each Wrong Option is Incorrect**
* **Option A:** Patch testing is a diagnostic tool used to identify contact allergens that cause skin lesions. While patch testing may be helpful in diagnosing contact dermatitis, it is not the most appropriate test for diagnosing solar dermatitis or PMLE.
* **Option B:** Biopsy is a diagnostic procedure that involves taking a tissue sample from the affected skin for histopathological examination. While a biopsy may be helpful in diagnosing certain skin conditions, it is not typically required for the diagnosis of PMLE, which can often be diagnosed based on clinical presentation and history.
* **Option C:** Skin prick test is a diagnostic tool used to identify allergens that cause allergic reactions. While skin prick testing may be helpful in diagnosing allergic conditions, it is not relevant to the diagnosis of PMLE, which is a photodermatosis rather than an allergic condition.
**Clinical Pearl / High-Yield Fact**
PMLE is a common condition that affects up to 20% of the population in certain regions, and its symptoms can be mistaken for other skin conditions, such as eczema or contact dermatitis. A thorough history of symptom exacerbation in the summer months and improvement in the winter months is crucial for making a diagnosis.
**Correct Answer:** C.