Phototherapy and Photobiology Practice Questions

Q: A 12-year-old boy develops pruritic hemorrhagic vesicles on his cheeks, ears, nose, and hands 12 hours after spending his holiday at Kovalam beach. A week later, the lesions crusted and healed with permanent scars. What is the most probable diagnosis?

Phytophotodermatitis. ***Phytophotodermatitis*** - This condition occurs when **skin comes into contact with photosensitizing plant compounds (furocoumarins)** and is then exposed to **UVA light**, leading to a phototoxic reaction. - The presentation of **pruritic hemorrhagic vesicles** on sun-exposed areas (cheeks, ears, nose, hands) after beach exposure, followed by scabbing and **permanent scarring**, is classic for phytophotodermatitis. *Pityriasis rosea* - Characterized by an **initial "herald patch"** followed by smaller, oval, pinkish-red patches with fine scales, often arranged in a **"Christmas tree" pattern** on the trunk. - It is typically **self-limiting**, does not involve hemorrhagic vesicles or scarring, and is not directly triggered by sun exposure. *Pityriasis rubra pilaris* - A chronic condition characterized by **follicular papules** that coalesce into **reddish-orange plaques** with islands of normal skin, often starting on the scalp, neck, and upper trunk. - It does not present with acute hemorrhagic vesicles or follow sun exposure in this manner, and scarring is not a typical outcome. *Dermatitis herpetiformis* - An intensely itchy, chronic blistering skin condition associated with **gluten-sensitive enteropathy (celiac disease)**, characterized by symmetrically distributed papulovesicular lesions, often on the elbows, knees, buttocks, and scalp. - While it involves pruritic vesicles, the hemorrhagic nature, specific distribution following sun exposure, and subsequent scarring do not align with dermatitis herpetiformis.

Q: A 20-year-old woman presents with pruritic, erythematous, scaly lesions on her face and neck that worsen with sun exposure. What is the most likely diagnosis?

Polymorphous light eruption (PMLE). ***Polymorphous light eruption (PMLE)*** - PMLE is the **most common photodermatosis**, typically affecting young women in their 20s-40s, perfectly matching this patient's demographic. - Presents with **pruritic, erythematous papules, plaques, or vesicles** on **sun-exposed areas** (face, neck, décolletage, arms) that appear or worsen after sun exposure. - Lesions typically develop within **hours to days** after sun exposure and may have a scaly appearance, directly aligning with the clinical presentation. - The condition is more common in **spring/early summer** when sun exposure increases after winter months. *Systemic lupus erythematosus* - While **photosensitivity** is a feature of SLE, the classic rash is a **malar (butterfly) rash** or discoid lesions with a different morphology. - SLE typically presents with **systemic symptoms** such as arthralgia, fatigue, fever, or kidney involvement, which are not mentioned here. - SLE is less common than PMLE and would require additional clinical and serological evidence (ANA, anti-dsDNA). *Rosacea* - Rosacea typically presents with **facial erythema, telangiectasias, papules, and pustules** on the central face (cheeks, nose, chin, forehead). - While sun exposure can trigger flares, **significant pruritus and scaling** are not characteristic features of rosacea. - Rosacea does not typically extend to the neck and lacks the acute photosensitive pattern seen here. *Seborrheic dermatitis* - Characterized by **erythematous patches with greasy, yellowish scales** in sebum-rich areas (scalp, eyebrows, nasolabial folds, chest). - **Not exacerbated by sun exposure**—this is the key differentiating feature from photodermatoses. - While it can affect the face, the relationship to sun exposure and the distribution pattern favor PMLE.

Q: In which of the following conditions is phototherapy, specifically ultraviolet light therapy, useful for treatment?

Psoriasis. ***Psoriasis*** - **Phototherapy** (narrowband UVB, broadband UVB, or PUVA) is a **well-established first-line treatment** for **moderate-to-severe psoriasis**. - It works by **suppressing overactive immune cells** in the skin, reducing inflammation and decreasing keratinocyte proliferation. - **Direct therapeutic effect** on active psoriatic lesions makes this the primary indication for phototherapy in dermatology. *Tinea corporis* - **Tinea corporis** is a **superficial fungal infection** (dermatophytosis) of the skin. - Requires **antifungal medications** (topical azoles or oral terbinafine/griseofulvin) for treatment. - **Phototherapy has no antifungal activity** and is not used for this condition. *Pemphigus* - **Pemphigus** is an **autoimmune blistering disease** with intraepidermal acantholysis. - Treatment requires **systemic immunosuppression** (corticosteroids, rituximab, azathioprine). - **Phototherapy is not indicated** and could potentially worsen the condition. *PMLE* - **Polymorphous light eruption (PMLE)** is a common **photosensitivity disorder**. - While **prophylactic photohardening** (gradual controlled UV exposure) can be used to build tolerance **before sun exposure season**, this is a **preventative desensitization strategy**, not treatment of active disease. - Unlike psoriasis, phototherapy does **not treat active PMLE lesions** and can trigger flares if not done properly. - The primary approach for active PMLE is **sun avoidance, sun protection, and topical corticosteroids**.

Q: Which type of ultraviolet radiation causes the most skin disorders?

UV-B. ***UV-B*** - **UV-B radiation** is a major cause of **sunburn** and directly damages DNA, leading to most **skin cancers** (basal cell carcinoma, squamous cell carcinoma, and melanoma). - It plays a significant role in photoaging and the development of most **skin disorders** related to sun exposure. *UV-A* - **UV-A radiation** penetrates deeper into the skin than UV-B and is primarily associated with **photoaging**, producing wrinkles and fine lines. - While it contributes to skin cancer development, its direct role in DNA damage and sunburn is less than that of UV-B. *UV-C* - **UV-C radiation** is the most damaging type of UV light, but it is almost entirely **absorbed by the Earth's ozone layer** and does not reach the Earth's surface. - Therefore, it does not typically cause skin disorders in humans under natural conditions. *None of the options* - This option is incorrect because **UV-B radiation** is well-established as a primary cause of numerous skin disorders, including most skin cancers and sunburn.

Question 1

A 12-year-old boy develops pruritic hemorrhagic vesicles on his cheeks, ears, nose, and hands 12 hours after spending his holiday at Kovalam beach. A week later, the lesions crusted and healed with permanent scars. What is the most probable diagnosis?

Accepted Answer

Phytophotodermatitis

Answer

Dermatitis herpetiformis

Answer

Pityriasis rosea

Answer

Pityriasis rubra pilaris

Question 2

A 20-year-old woman presents with pruritic, erythematous, scaly lesions on her face and neck that worsen with sun exposure. What is the most likely diagnosis?

Accepted Answer

Polymorphous light eruption (PMLE)

Answer

Systemic lupus erythematosus

Answer

Rosacea

Answer

Seborrheic dermatitis

Question 3

In which of the following conditions is phototherapy, specifically ultraviolet light therapy, useful for treatment?

Accepted Answer

Psoriasis

Answer

Tinea corporis

Answer

Pemphigus

Answer

PMLE

Question 4

Which type of ultraviolet radiation causes the most skin disorders?

Accepted Answer

UV-B

Answer

UV-A

Answer

UV-C

Answer

None of the options

Phototherapy and Photobiology — MCQs

Phototherapy and Photobiology — MCQs

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