Phototherapy and Photobiology — MCQs

Q: Which of the following is NOT a complication of PUVA therapy?

Exfoliative dermatitis. **Explanation:** PUVA (Psoralen + Ultraviolet A) therapy involves the administration of a photosensitizer (8-methoxypsoralen) followed by exposure to UVA radiation. While it is an effective treatment for conditions like psoriasis and vitiligo, it carries specific long-term and short-term risks. **Why Exfoliative Dermatitis is the correct answer:** Exfoliative dermatitis (Erythroderma) is **not** a direct complication of PUVA. In fact, PUVA is often used as a *treatment* modality for certain types of exfoliative dermatitis, such as those caused by Mycosis Fungoides or Psoriasis. While PUVA can cause a "PUVA itch" or a phototoxic burn (erythema), it does not typically trigger generalized exfoliation. **Analysis of Incorrect Options:** * **Premature aging of the skin (Dermatoheliosis):** Chronic UVA exposure leads to the degradation of collagen and elastin fibers, resulting in wrinkles, lentigines, and telangiectasia. * **Cataracts:** Psoralens distribute to the lens of the eye. If the eyes are not protected with UVA-blocking sunglasses for 24 hours post-ingestion, UVA exposure can lead to lens opacification. * **Skin cancers:** PUVA is mutagenic. Long-term therapy significantly increases the risk of Non-Melanoma Skin Cancers (NMSC), particularly **Squamous Cell Carcinoma (SCC)**. **High-Yield Clinical Pearls for NEET-PG:** * **Most common acute side effect:** Erythema (phototoxicity) and pruritus. * **Most common long-term risk:** Squamous Cell Carcinoma (SCC) is more common than Basal Cell Carcinoma (BCC) in PUVA patients (reversing the usual ratio). * **PUVA Lentigines:** Distinctive, irregular pigmented macules that appear after chronic therapy. * **Contraindications:** Pregnancy, lactation, history of skin cancer (Xeroderma Pigmentosum), and severe hepatic/renal failure.

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

Hydroa vacciniforme. **Explanation:** The clinical presentation of a young boy with **hemorrhagic vesicles** on sun-exposed areas (cheeks, ears, nose, hands) that heal with **permanent scarring** (varioliform scars) is pathognomonic for **Hydroa vacciniforme (HV)**. **Why Hydroa vacciniforme is correct:** HV is a rare, chronic photodermatosis primarily affecting children. It is triggered by UVA radiation. The hallmark is the progression from erythema to vesicles/bullae, which become umbilicated and hemorrhagic, eventually forming necrotic crusts. The defining feature for NEET-PG is the healing process, which results in **depressed, "vacciniform" (smallpox-like) scars**. It is often associated with **Epstein-Barr Virus (EBV)** infection. **Why other options are incorrect:** * **Polymorphic Light Eruption (PMLE):** The most common photodermatosis. While it causes pruritic papules or vesicles, it **never heals with scarring**. * **Actinic Prurigo:** A variant of PMLE common in Native Americans. It presents with intensely pruritic, excoriated papules and nodules, often involving the lips (cheilitis) and conjunctiva, but does not typically present with hemorrhagic vesicles and varioliform scarring. * **Persistent Light Reaction:** Now classified under Chronic Actinic Dermatitis. It is an eczematous reaction seen in elderly males, where skin remains sensitive to light even without allergen exposure. **High-Yield Clinical Pearls for NEET-PG:** * **Action Spectrum:** UVA is the primary trigger for HV. * **Association:** Severe, systemic cases of HV are linked to **EBV-associated T-cell lymphoproliferative disorders**. * **Differential Diagnosis:** Must be distinguished from Erythropoietic Protoporphyria (EPP), which presents with immediate burning pain and waxy scarring, but lacks the hemorrhagic bullae of HV. * **Management:** Strict photoprotection; severe cases may require antimalarials or immunosuppressants.

Q: Psoralen plus ultraviolet A (PUVA) therapy is useful in which of the following conditions?

All of the above. **Explanation:** **PUVA (Psoralen + UVA)** therapy involves the administration of a photosensitizing agent (8-Methoxypsoralen) followed by exposure to long-wave ultraviolet A light (320–400 nm). The mechanism involves the formation of DNA photo-adducts, which inhibit DNA synthesis and induce apoptosis of hyperproliferating cells and T-lymphocytes. **Why "All of the Above" is Correct:** * **Psoriasis:** PUVA is a classic treatment for moderate-to-severe plaque psoriasis. It reduces the rapid turnover of keratinocytes and suppresses the local cutaneous immune response. * **Vitiligo:** Psoralens stimulate the migration and proliferation of melanocytes from the hair follicle reservoir to the depigmented skin, promoting repigmentation. * **Mycosis Fungoides (MF):** As a cutaneous T-cell lymphoma, MF is highly sensitive to the phototoxic effects of PUVA, which induces apoptosis in malignant T-cells infiltrating the epidermis. **Clinical Pearls for NEET-PG:** 1. **Mechanism:** Psoralens intercalate into DNA; UVA then causes **Type I (oxygen-independent)** reactions forming monoadducts/cross-links and **Type II (oxygen-dependent)** reactions forming free radicals. 2. **Dosage:** Oral psoralen is usually given **0.6 mg/kg**, 2 hours before UVA exposure. 3. **Side Effects:** Acute side effects include nausea and erythema. Long-term risks include **PUVA lentigines** and an increased risk of **Squamous Cell Carcinoma (SCC)**. 4. **Contraindication:** PUVA is contraindicated in patients with Xeroderma Pigmentosum, Lupus Erythematosus, and pregnancy. 5. **Current Trend:** Narrowband UVB (311 nm) has largely replaced PUVA for psoriasis and vitiligo due to a better safety profile, but PUVA remains superior for thick plaques and MF.

Q: Psoralen is used in the treatment of:

Vitiligo. **Explanation:** **Psoralen** is a photosensitizing agent used in **PUVA (Psoralen + Ultraviolet A)** therapy. It belongs to the furocoumarin family and works by intercalating into DNA. Upon exposure to UVA light, it forms DNA cross-links, which inhibits keratinocyte proliferation and induces melanocyte stimulation. **Why Vitiligo is correct:** In Vitiligo, PUVA therapy is a classic treatment modality. It works by: 1. **Immunomodulation:** Suppressing the T-cell mediated destruction of melanocytes. 2. **Melanocyte Stimulation:** Promoting the migration of melanocytes from the hair follicle reservoir to the depigmented skin, leading to repigmentation. **Why other options are incorrect:** * **Pemphigus:** This is an autoimmune bullous disorder treated primarily with systemic corticosteroids and immunosuppressants (e.g., Rituximab, Azathioprine), not phototherapy. * **Pityriasis alba:** This is a mild form of dermatitis common in children, usually associated with atopy. It is treated with emollients and low-potency topical steroids; psoralens are not indicated. * **Ichthyosis:** This is a genetic disorder of keratinization characterized by fish-like scales. Treatment involves keratolytics (e.g., urea, lactic acid) and systemic retinoids. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Psoralens (e.g., 8-Methoxypsoralen) bind to pyrimidine bases (thymine) in DNA. * **Common Indications for PUVA:** Psoriasis (most common), Vitiligo, Mycosis Fungoides (CTCL), and Alopecia Areata. * **Side Effects:** Acute side effects include nausea and polymorphic light eruption. Long-term risks include **PUVA lentigines** and an increased risk of **Squamous Cell Carcinoma (SCC)**. * **Contraindication:** PUVA is contraindicated in patients with Xeroderma Pigmentosum, SLE, or a history of skin cancer.

Q: What is the wavelength range of UVB rays?

290 - 320 nm. **Explanation:** The electromagnetic spectrum of ultraviolet (UV) radiation is divided into three bands based on wavelength and biological activity: UVA, UVB, and UVC. **1. Why Option A is Correct:** **UVB (290–320 nm)** is known as the "erythemal" or "sunburn" spectrum. It is the range responsible for delayed tanning, vitamin D synthesis, and the development of skin cancers (basal and squamous cell carcinomas). In clinical practice, **Narrowband UVB (311–313 nm)** is the gold standard for treating conditions like vitiligo and psoriasis due to its high efficacy and lower carcinogenic risk compared to broadband. **2. Analysis of Incorrect Options:** * **Options B & C (320–400 nm):** These fall within the **UVA** range. UVA is further divided into UVA2 (320–340 nm) and UVA1 (340–400 nm). UVA is responsible for immediate tanning and photoaging (dermatoheliosis) as it penetrates deeper into the dermis. * **Option D (390–420 nm):** This range transitions from the long-wave UVA spectrum into **Visible Light** (starting at approximately 400 nm). **3. High-Yield Clinical Pearls for NEET-PG:** * **UVC (200–290 nm):** Shortest wavelength, highest energy; mostly absorbed by the ozone layer. Used in germicidal lamps. * **Minimal Erythema Dose (MED):** The smallest dose of UV radiation that produces confluent erythema at 24 hours. UVB is 1000 times more erythrogenic than UVA. * **Photoaging:** Primarily caused by UVA (A for Aging). * **Phototherapy:** PUVA (Psoralen + UVA) uses the 320–400 nm range, while NB-UVB uses 311 nm.

Phototherapy and Photobiology Indian Medical PG Practice Questions and MCQs

Question 1: Which of the following is NOT a complication of PUVA therapy?

A. Premature aging of the skin
B. Cataracts
C. Skin cancers
D. Exfoliative dermatitis (Correct Answer)

Explanation: **Explanation:** PUVA (Psoralen + Ultraviolet A) therapy involves the administration of a photosensitizer (8-methoxypsoralen) followed by exposure to UVA radiation. While it is an effective treatment for conditions like psoriasis and vitiligo, it carries specific long-term and short-term risks. **Why Exfoliative Dermatitis is the correct answer:** Exfoliative dermatitis (Erythroderma) is **not** a direct complication of PUVA. In fact, PUVA is often used as a *treatment* modality for certain types of exfoliative dermatitis, such as those caused by Mycosis Fungoides or Psoriasis. While PUVA can cause a "PUVA itch" or a phototoxic burn (erythema), it does not typically trigger generalized exfoliation. **Analysis of Incorrect Options:** * **Premature aging of the skin (Dermatoheliosis):** Chronic UVA exposure leads to the degradation of collagen and elastin fibers, resulting in wrinkles, lentigines, and telangiectasia. * **Cataracts:** Psoralens distribute to the lens of the eye. If the eyes are not protected with UVA-blocking sunglasses for 24 hours post-ingestion, UVA exposure can lead to lens opacification. * **Skin cancers:** PUVA is mutagenic. Long-term therapy significantly increases the risk of Non-Melanoma Skin Cancers (NMSC), particularly **Squamous Cell Carcinoma (SCC)**. **High-Yield Clinical Pearls for NEET-PG:** * **Most common acute side effect:** Erythema (phototoxicity) and pruritus. * **Most common long-term risk:** Squamous Cell Carcinoma (SCC) is more common than Basal Cell Carcinoma (BCC) in PUVA patients (reversing the usual ratio). * **PUVA Lentigines:** Distinctive, irregular pigmented macules that appear after chronic therapy. * **Contraindications:** Pregnancy, lactation, history of skin cancer (Xeroderma Pigmentosum), and severe hepatic/renal failure.

Question 2: A 12-year-old boy, after spending his holiday on a beach, develops pruritic hemorrhagic vesicles on his cheeks, ears, nose, and hands 12 hours after sun exposure. A week later, the lesions crusted and healed with permanent scars. What is the most probable diagnosis?

A. Polymorphic light eruption
B. Hydroa vacciniforme (Correct Answer)
C. Actinic prurigo
D. Persistent light reaction

Explanation: **Explanation:** The clinical presentation of a young boy with **hemorrhagic vesicles** on sun-exposed areas (cheeks, ears, nose, hands) that heal with **permanent scarring** (varioliform scars) is pathognomonic for **Hydroa vacciniforme (HV)**. **Why Hydroa vacciniforme is correct:** HV is a rare, chronic photodermatosis primarily affecting children. It is triggered by UVA radiation. The hallmark is the progression from erythema to vesicles/bullae, which become umbilicated and hemorrhagic, eventually forming necrotic crusts. The defining feature for NEET-PG is the healing process, which results in **depressed, "vacciniform" (smallpox-like) scars**. It is often associated with **Epstein-Barr Virus (EBV)** infection. **Why other options are incorrect:** * **Polymorphic Light Eruption (PMLE):** The most common photodermatosis. While it causes pruritic papules or vesicles, it **never heals with scarring**. * **Actinic Prurigo:** A variant of PMLE common in Native Americans. It presents with intensely pruritic, excoriated papules and nodules, often involving the lips (cheilitis) and conjunctiva, but does not typically present with hemorrhagic vesicles and varioliform scarring. * **Persistent Light Reaction:** Now classified under Chronic Actinic Dermatitis. It is an eczematous reaction seen in elderly males, where skin remains sensitive to light even without allergen exposure. **High-Yield Clinical Pearls for NEET-PG:** * **Action Spectrum:** UVA is the primary trigger for HV. * **Association:** Severe, systemic cases of HV are linked to **EBV-associated T-cell lymphoproliferative disorders**. * **Differential Diagnosis:** Must be distinguished from Erythropoietic Protoporphyria (EPP), which presents with immediate burning pain and waxy scarring, but lacks the hemorrhagic bullae of HV. * **Management:** Strict photoprotection; severe cases may require antimalarials or immunosuppressants.

Question 3: Psoralen plus ultraviolet A (PUVA) therapy is useful in which of the following conditions?

A. Vitiligo
B. Mycosis fungoides
C. Psoriasis
D. All of the above (Correct Answer)

Explanation: **Explanation:** **PUVA (Psoralen + UVA)** therapy involves the administration of a photosensitizing agent (8-Methoxypsoralen) followed by exposure to long-wave ultraviolet A light (320–400 nm). The mechanism involves the formation of DNA photo-adducts, which inhibit DNA synthesis and induce apoptosis of hyperproliferating cells and T-lymphocytes. **Why "All of the Above" is Correct:** * **Psoriasis:** PUVA is a classic treatment for moderate-to-severe plaque psoriasis. It reduces the rapid turnover of keratinocytes and suppresses the local cutaneous immune response. * **Vitiligo:** Psoralens stimulate the migration and proliferation of melanocytes from the hair follicle reservoir to the depigmented skin, promoting repigmentation. * **Mycosis Fungoides (MF):** As a cutaneous T-cell lymphoma, MF is highly sensitive to the phototoxic effects of PUVA, which induces apoptosis in malignant T-cells infiltrating the epidermis. **Clinical Pearls for NEET-PG:** 1. **Mechanism:** Psoralens intercalate into DNA; UVA then causes **Type I (oxygen-independent)** reactions forming monoadducts/cross-links and **Type II (oxygen-dependent)** reactions forming free radicals. 2. **Dosage:** Oral psoralen is usually given **0.6 mg/kg**, 2 hours before UVA exposure. 3. **Side Effects:** Acute side effects include nausea and erythema. Long-term risks include **PUVA lentigines** and an increased risk of **Squamous Cell Carcinoma (SCC)**. 4. **Contraindication:** PUVA is contraindicated in patients with Xeroderma Pigmentosum, Lupus Erythematosus, and pregnancy. 5. **Current Trend:** Narrowband UVB (311 nm) has largely replaced PUVA for psoriasis and vitiligo due to a better safety profile, but PUVA remains superior for thick plaques and MF.

Question 4: Psoralen is used in the treatment of:

A. Pemphigus
B. Vitiligo (Correct Answer)
C. Pityriasis alba
D. Ichthyosis

Explanation: **Explanation:** **Psoralen** is a photosensitizing agent used in **PUVA (Psoralen + Ultraviolet A)** therapy. It belongs to the furocoumarin family and works by intercalating into DNA. Upon exposure to UVA light, it forms DNA cross-links, which inhibits keratinocyte proliferation and induces melanocyte stimulation. **Why Vitiligo is correct:** In Vitiligo, PUVA therapy is a classic treatment modality. It works by: 1. **Immunomodulation:** Suppressing the T-cell mediated destruction of melanocytes. 2. **Melanocyte Stimulation:** Promoting the migration of melanocytes from the hair follicle reservoir to the depigmented skin, leading to repigmentation. **Why other options are incorrect:** * **Pemphigus:** This is an autoimmune bullous disorder treated primarily with systemic corticosteroids and immunosuppressants (e.g., Rituximab, Azathioprine), not phototherapy. * **Pityriasis alba:** This is a mild form of dermatitis common in children, usually associated with atopy. It is treated with emollients and low-potency topical steroids; psoralens are not indicated. * **Ichthyosis:** This is a genetic disorder of keratinization characterized by fish-like scales. Treatment involves keratolytics (e.g., urea, lactic acid) and systemic retinoids. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Psoralens (e.g., 8-Methoxypsoralen) bind to pyrimidine bases (thymine) in DNA. * **Common Indications for PUVA:** Psoriasis (most common), Vitiligo, Mycosis Fungoides (CTCL), and Alopecia Areata. * **Side Effects:** Acute side effects include nausea and polymorphic light eruption. Long-term risks include **PUVA lentigines** and an increased risk of **Squamous Cell Carcinoma (SCC)**. * **Contraindication:** PUVA is contraindicated in patients with Xeroderma Pigmentosum, SLE, or a history of skin cancer.

Question 5: What is the wavelength range of UVB rays?

A. 290 - 320 nm (Correct Answer)
B. 320 - 360 nm
C. 360 - 390 nm
D. 390 - 420 nm

Explanation: **Explanation:** The electromagnetic spectrum of ultraviolet (UV) radiation is divided into three bands based on wavelength and biological activity: UVA, UVB, and UVC. **1. Why Option A is Correct:** **UVB (290–320 nm)** is known as the "erythemal" or "sunburn" spectrum. It is the range responsible for delayed tanning, vitamin D synthesis, and the development of skin cancers (basal and squamous cell carcinomas). In clinical practice, **Narrowband UVB (311–313 nm)** is the gold standard for treating conditions like vitiligo and psoriasis due to its high efficacy and lower carcinogenic risk compared to broadband. **2. Analysis of Incorrect Options:** * **Options B & C (320–400 nm):** These fall within the **UVA** range. UVA is further divided into UVA2 (320–340 nm) and UVA1 (340–400 nm). UVA is responsible for immediate tanning and photoaging (dermatoheliosis) as it penetrates deeper into the dermis. * **Option D (390–420 nm):** This range transitions from the long-wave UVA spectrum into **Visible Light** (starting at approximately 400 nm). **3. High-Yield Clinical Pearls for NEET-PG:** * **UVC (200–290 nm):** Shortest wavelength, highest energy; mostly absorbed by the ozone layer. Used in germicidal lamps. * **Minimal Erythema Dose (MED):** The smallest dose of UV radiation that produces confluent erythema at 24 hours. UVB is 1000 times more erythrogenic than UVA. * **Photoaging:** Primarily caused by UVA (A for Aging). * **Phototherapy:** PUVA (Psoralen + UVA) uses the 320–400 nm range, while NB-UVB uses 311 nm.

Practice by Chapter

Fundamentals of Photobiology

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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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