Phototherapy and Photobiology — MCQs

Phototherapy and Photobiology Indian Medical PG Practice Questions and MCQs

Question 31: A 50-year-old male with a history of liver disease presents with a photosensitive, blistering rash on his hands. What is the most likely diagnosis?

A. Porphyria cutanea tarda (Correct Answer)
B. Herpes simplex
C. Bullous pemphigoid
D. Pemphigus vulgaris

Explanation: ***Porphyria cutanea tarda*** - The classic triad of **photosensitive blistering on sun-exposed areas** (especially dorsal hands), **fragile skin**, and **association with liver disease** makes PCT the most likely diagnosis. - Caused by deficiency of **uroporphyrinogen decarboxylase**, leading to accumulation of photoreactive porphyrins in the skin. - Strong associations include **hepatitis C, alcohol-related liver disease, hemochromatosis**, and estrogen use. - Characteristic findings: vesicles, bullae, erosions, milia, and hyperpigmentation on sun-exposed areas. *Herpes simplex* - Presents as **grouped vesicles on an erythematous base**, often with prodrome of tingling or burning. - Not characteristically photosensitive and **no association with liver disease**. - Lesions are typically recurrent in the same location and resolve with crusting. *Bullous pemphigoid* - An **autoimmune subepidermal blistering disease** with tense bullae and intense pruritus. - Typically affects elderly patients but **not associated with photosensitivity or liver disease**. - Blisters can occur on any body site, not specifically sun-exposed areas. *Pemphigus vulgaris* - An **autoimmune intraepidermal blistering disease** with flaccid bullae that easily rupture, leaving painful erosions. - Often involves **mucous membranes** (oral cavity most common). - **No association with photosensitivity or liver disease**.

Question 32: 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?

A. Dermatitis herpetiformis
B. Pityriasis rosea
C. Pityriasis rubra pilaris
D. Phytophotodermatitis (Correct Answer)

Explanation: ***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.

Question 33: 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?

A. Systemic lupus erythematosus
B. Rosacea
C. Polymorphous light eruption (PMLE) (Correct Answer)
D. Seborrheic dermatitis

Explanation: ***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.

Question 34: Which of the following statements about actinic lichen planus is false?

A. Associated with severe pruritus (Correct Answer)
B. Violaceous brown papules
C. Usually affects exposed areas of body
D. Autoimmune etiology

Explanation: ***Associated with severe pruritus*** - While other forms of lichen planus, especially the typical cutaneous type, are often associated with **severe pruritus**, actinic lichen planus is typically characterized by **mild or absent pruritus**. - Its presentation is often more focused on pigmentary changes and papules in sun-exposed areas rather than intense itching. *Autoimmune etiology* - **Lichen planus**, including its actinic variant, is recognized as an **autoimmune disease**. - It involves a **T-cell-mediated immune response** against basal keratinocytes. *Violaceous brown papules* - Actinic lichen planus commonly presents with **violaceous, brown, or hyperpigmented papules and plaques**. - These lesions often exhibit a subtle **annular or reticulated pattern**. *Usually affects exposed areas of body* - As its name suggests ("actinic" referring to light), this variant of lichen planus preferentially affects **sun-exposed areas** such as the face, neck, and dorsal hands. - This distribution distinguishes it from classic lichen planus, which can occur anywhere but often affects the flexor surfaces of the wrists, ankles, and oral mucosa.

Question 35: In which of the following conditions is phototherapy, specifically ultraviolet light therapy, useful for treatment?

A. Psoriasis (Correct Answer)
B. Tinea corporis
C. Pemphigus
D. PMLE

Explanation: ***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**.

Question 36: What is the primary purpose of UV rays examination in dermatology?

A. Assessing pigmentary disorders (Correct Answer)
B. Detecting porphyria
C. Diagnosing fungal infections
D. Detecting bacterial infections

Explanation: ***Assessing pigmentary disorders*** - **UV light** (specifically **Wood's lamp** examination) enhances the contrast between pigmented and non-pigmented areas of the skin, making **vitiligo**, **melasma**, and other **pigmentary changes** more apparent. - This increased visibility allows for better delineation of lesion borders and estimation of the extent of pigmentary abnormalities, aiding in diagnosis and treatment planning. - This is the **most common and primary clinical application** of Wood's lamp in dermatology. *Diagnosing fungal infections* - While a **Wood's lamp** can sometimes highlight certain fungal infections like **tinea capitis** caused by **Microsporum species** (due to **fluorescence**), it is not the primary or definitive diagnostic tool. - **Microscopy with KOH prep** and **fungal culture** are the gold standard for diagnosing fungal infections. - Most modern dermatophytes do not fluoresce, limiting its utility. *Detecting porphyria* - Certain types of **porphyria** (e.g., **porphyria cutanea tarda**) can cause **red-pink fluorescence of urine** or teeth under **UV light**, but this is a systemic finding, not a primary dermatological examination purpose. - Diagnosis of **porphyria** primarily relies on **laboratory tests** measuring porphyrin levels in blood, urine, and stool. *Detecting bacterial infections* - While certain bacteria (such as **Corynebacterium minutissimum** causing **erythrasma**) show **coral-red fluorescence** under Wood's lamp, this is a specific diagnostic application, not the primary purpose. - Most bacterial skin infections do not fluoresce, and culture/clinical examination remain the primary diagnostic methods.

Question 37: Which type of ultraviolet radiation causes the most skin disorders?

A. UV-A
B. UV-B (Correct Answer)
C. UV-C
D. None of the options

Explanation: ***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 38: Exposure to sunlight can precipitate chronic disc-shaped skin lesions characteristic of which of the following conditions?

A. Dermatitis herpetiformis
B. Lupus vulgaris
C. Chloasma
D. Discoid lupus erythematosus (Correct Answer)

Explanation: ***Discoid lupus erythematosus*** - This condition is a **chronic cutaneous form of lupus** characterized by distinctive **disc-shaped lesions**, often on sun-exposed areas. - **Photosensitivity** is a prominent feature, meaning sunlight direct exposure often **exacerbates or triggers these lesions**. *Chloasma* - This refers to **melasma**, a common condition causing **dark, discolored patches** on the skin, often triggered by **hormonal changes** (e.g., pregnancy) and sun exposure. It does not typically form disc-shaped lesions. - While sunlight exposure influences its presentation, it lacks the characteristic **inflammatory disc-shaped lesions** of discoid lupus. *Dermatitis herpetiformis* - This is an **autoimmune blistering skin condition** strongly associated with **celiac disease**, characterized by intensely pruritic papules and vesicles, not disc-shaped lesions. - Its lesions are **itchy, erythematous papules and vesicles** that are symmetrically distributed, and it is not directly precipitated by sunlight exposure. *Lupus vulgaris* - This is a form of **cutaneous tuberculosis** presenting as slowly progressive, ulcerative, and destructive skin lesions. It is caused by **Mycobacterium tuberculosis** and is unrelated to sun exposure. - It involves direct **tuberculous infection of the skin**, and its clinical presentation differs significantly from the autoimmune, photosensitivity-driven lesions of discoid lupus erythematosus.

Question 39: What is the optimal wavelength of light emitted by a Wood's lamp for dermatological examinations?

A. 365 nm (Correct Answer)
B. 400 nm
C. 320 nm
D. 200 nm

Explanation: **365 nm** - A Wood's lamp primarily emits **long-wave UVA light** in the 320 to 400 nm range, with an optimal peak around **365 nm**. - This specific wavelength is ideal for inducing **fluorescence** in various dermatological conditions, making them visible. *400 nm* - While within the UVA range, **400 nm** is at the higher end and may not provide the optimal fluorescence yield for all diagnostic purposes compared to 365 nm. - Light at 400 nm is closer to the visible light spectrum and might offer less distinction for subtle fluorescence. *320 nm* - **320 nm** is at the lower end of the UVA spectrum, bordering on UVB. - While still capable of inducing some fluorescence, it is generally less effective than 365 nm for the conditions typically examined with a Wood's lamp. *200 nm* - **200 nm** falls into the **UVC range** (100-280 nm), which is harmful and not used for diagnostic purposes in a Wood's lamp. - This wavelength is absorbed by the atmosphere and epidermis and can cause significant **DNA damage**, making it unsafe for routine dermatological examination.

Practice by Chapter

Fundamentals of Photobiology

Practice Questions

UVA and UVB Phototherapy

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PUVA Therapy

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Narrow-Band UVB Therapy

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Excimer Laser Therapy

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Photodynamic Therapy

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Phototoxicity and Photoallergy

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Photoprotection

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Sunscreens

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Photoaging

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Phototherapy Protocols

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Management of Phototherapy Side Effects

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