Phototherapy and Photobiology Practice Questions

Q: A 45-year-old farmer presents with itchy erythematous papular lesions on the face, neck, 'V' area of the chest, and dorsum of hands and forearms, present for 3 years. The lesions are more severe in summers and improve in winters. What is the most appropriate diagnostic test for this condition?

Skin biopsy. ### Explanation **Diagnosis: Chronic Actinic Dermatitis (CAD)** The clinical presentation—a middle-aged farmer with itchy, erythematous lesions in a **photo-distributed pattern** (face, V-area of chest, dorsum of hands) that exacerbates in summer—is classic for **Chronic Actinic Dermatitis (CAD)**. CAD is an immunologically mediated photodermatosis that often begins as an eczematous reaction to light. **1. Why Skin Biopsy is the Correct Answer:** While the diagnosis of CAD is primarily clinical, a **skin biopsy** is the most appropriate diagnostic step to confirm the diagnosis and, more importantly, to **rule out mimics** like Mycosis Fungoides (Cutaneous T-cell Lymphoma). Histopathology in CAD typically shows an eczematous pattern (spongiosis) or, in severe cases (Actinic Reticuloid), a dense dermal infiltrate that can resemble lymphoma. **2. Why Other Options are Incorrect:** * **Patch Test (Option C):** While many CAD patients have associated contact allergies (e.g., to Compositae plants or fragrances), a patch test identifies contact allergens, not the primary photosensitivity. A *Photo-patch test* would be more relevant, but biopsy remains the gold standard for definitive characterization. * **Estimation of IgE (Option B):** Elevated IgE is a marker for Atopic Dermatitis, not photodermatoses. * **Intradermal Prick Test (Option D):** This is used to diagnose Type I hypersensitivity (e.g., allergic rhinitis or asthma) and has no role in diagnosing CAD. **Clinical Pearls for NEET-PG:** * **CAD Spectrum:** Includes Photosensitive Eczema and Actinic Reticuloid. * **Demographics:** Typically affects elderly males (often outdoor workers like farmers). * **Photo-testing:** Patients show a **reduced Minimal Erythema Dose (MED)** to UVA, UVB, and sometimes visible light. * **Management:** Strict photoprotection, topical steroids, and in refractory cases, systemic immunosuppressants (Azathioprine).

Q: Which of the following tumors is not caused by PUVA therapy?

Cutaneous T-cell lymphoma. **Explanation:** PUVA (Psoralen + Ultraviolet A) therapy is a potent photochemotherapy used for various dermatological conditions. However, it is well-documented to be **carcinogenic** due to its ability to cause direct DNA damage (photo-adducts) and localized immunosuppression. **Why Cutaneous T-cell Lymphoma (CTCL) is the correct answer:** CTCL (such as Mycosis Fungoides) is **not caused** by PUVA; rather, PUVA is a primary **treatment modality** for early-stage CTCL. PUVA works by inducing apoptosis in malignant T-cells within the skin. It does not have a causal relationship with the development of lymphoid malignancies. **Analysis of Incorrect Options:** * **Squamous Cell Carcinoma (SCC):** This is the **most common** skin cancer associated with long-term PUVA therapy. The risk is dose-dependent and significantly increases after 200–250 treatments. * **Basal Cell Carcinoma (BCC):** While less common than SCC in the context of PUVA, the risk of BCC is still significantly elevated in patients receiving high cumulative doses of UVA. * **Melanoma:** Long-term follow-up studies (notably the 1975 PUVA Follow-up Study) have shown an increased risk of malignant melanoma, particularly 15 or more years after the first exposure to PUVA. **High-Yield Clinical Pearls for NEET-PG:** * **SCC vs. BCC Ratio:** In the general population, BCC is more common than SCC. However, in patients treated with **PUVA or Arsenic**, this ratio is **reversed** (SCC becomes more common than BCC). * **PUVA Lentigines:** These are distinct, stellate-shaped hyperpigmented macules that appear in PUVA-treated areas and serve as a marker of high cumulative UV exposure. * **Action Spectrum:** PUVA primarily uses UVA (320–400 nm), whereas UVB (290–320 nm) is used in Narrowband-UVB therapy.

Q: All are true regarding Polymorphous light eruption (PMLE), EXCEPT?

Face is always affected. **Explanation:** Polymorphous Light Eruption (PMLE) is the most common idiopathic primary photodermatosis. It is a delayed-type hypersensitivity reaction to an endogenous antigen induced by UV radiation. **Why Option D is the Correct Answer (The Exception):** The **face is frequently spared** in PMLE. This is due to the phenomenon of **"hardening"** (photo-tolerance). Areas chronically exposed to the sun, like the face and back of the hands, develop a tolerance to UV light. PMLE characteristically affects "intermittently exposed" areas, such as the V-area of the neck, forearms, and upper arms, especially during the first strong sun exposure of spring or summer. **Analysis of Other Options:** * **Option A & B:** PMLE is triggered by sunlight, specifically **UVA** (most common) and sometimes UVB or even artificial UV sources (tanning beds). The rash typically appears hours to days after exposure. * **Option C:** Despite the "polymorphic" nature of the lesions (papules, vesicles, or plaques), they are superficial and inflammatory. They resolve spontaneously within 7–10 days if further sun exposure is avoided, **healing without any permanent scarring.** **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Most common presentation is the **papular variant**. * **Seasonality:** Typically occurs in spring/early summer; improves as summer progresses due to the "hardening" effect. * **Gender Predilection:** More common in females (2:1 ratio). * **Management:** Photoprotection (broad-spectrum sunscreens) is first-line. Severe cases may require topical steroids or "prophylactic desensitization" using narrow-band UVB (NB-UVB) or PUVA.

Q: What is the treatment of choice for the cutaneous complications of porphyria?

Beta carotene. **Explanation:** The treatment of choice for the cutaneous complications of porphyria, specifically **Erythropoietic Protoporphyria (EPP)**, is **Oral Beta-carotene**. 1. **Mechanism of Correct Answer:** In porphyrias, the accumulation of porphyrins in the skin leads to photosensitivity. When exposed to light, these porphyrins generate reactive oxygen species (ROS) and singlet oxygen, causing lipid peroxidation and tissue damage. Beta-carotene acts as a potent **antioxidant and singlet oxygen scavenger**, thereby increasing the patient's tolerance to sunlight and reducing the severity of cutaneous phototoxicity. 2. **Analysis of Incorrect Options:** * **Intravenous Dextrose and Haematin (Options A & B):** These are the treatments of choice for **Acute Intermittent Porphyria (AIP)** and other acute hepatic porphyrias. They work by inhibiting the enzyme **ALA synthase** via feedback inhibition, thereby reducing the production of neurotoxic precursors. They do not treat cutaneous symptoms. * **Calamine (Option D):** This is a soothing topical agent used for pruritus and mild inflammatory conditions. It has no role in the underlying pathophysiology of porphyria-induced photosensitivity. **High-Yield Clinical Pearls for NEET-PG:** * **Erythropoietic Protoporphyria (EPP):** Most common porphyria in children; presents with immediate burning/pain upon sun exposure. * **Porphyria Cutanea Tarda (PCT):** Most common porphyria overall; presents with blisters and fragility on sun-exposed areas. Treatment involves **low-dose Chloroquine** or phlebotomy. * **Wood’s Lamp:** Urine in PCT shows **coral-red fluorescence**. * **Enzyme Deficiencies:** Remember **Uroporphyrinogen decarboxylase** for PCT and **Ferrochelatase** for EPP.

Q: Skin cancers develop due to sunlight exposure induced by which type of radiation?

UVB rays. **Explanation:** The primary driver of skin carcinogenesis (Basal Cell Carcinoma, Squamous Cell Carcinoma, and Melanoma) is **UVB radiation (290–320 nm)**. **Why UVB is the correct answer:** UVB rays are often referred to as "burning rays." They are directly absorbed by DNA, leading to the formation of **cyclobutane pyrimidine dimers (CPDs)**, specifically thymine dimers. If these mutations occur in tumor suppressor genes like **p53**, it leads to uncontrolled cell proliferation and skin cancer. While UVB has shorter wavelengths and less penetration than UVA, it is significantly more mutagenic. **Analysis of Incorrect Options:** * **UVA (320–400 nm):** Known as "aging rays," UVA penetrates deeper into the dermis, causing photoaging and indirect DNA damage via reactive oxygen species (ROS). While it contributes to skin cancer, it is less potent than UVB in direct mutagenesis. * **UVC (200–290 nm):** These are the most energetic and lethal rays; however, they are almost entirely absorbed by the Earth’s **ozone layer** and do not reach the skin under normal conditions. * **UVD:** This is a distractor; there is no such classification in the ultraviolet spectrum relevant to clinical dermatology. **High-Yield Clinical Pearls for NEET-PG:** * **Action Spectrum:** UVB is responsible for Vitamin D synthesis, sunburn (erythema), and the majority of non-melanoma skin cancers. * **Signature Mutation:** The "C to T" or "CC to TT" transition is the classic UV-induced mutation signature. * **Xeroderma Pigmentosum:** A condition where patients lack the **nucleotide excision repair (NER)** mechanism to fix UVB-induced pyrimidine dimers, leading to early-onset skin cancers. * **Sunscreen:** SPF (Sun Protection Factor) primarily measures protection against **UVB** rays.

Q: Which of the following skin conditions is treated with PUVA therapy?

Psoriasis. **Explanation** **PUVA (Psoralen + Ultraviolet A)** therapy is a form of photochemotherapy that combines the administration of a photosensitizing agent (Psoralen) with exposure to UVA radiation (320–400 nm). **1. Why Psoriasis is correct:** Psoriasis is a chronic inflammatory skin disorder characterized by keratinocyte hyperproliferation and T-cell mediated inflammation. PUVA works by intercalating Psoralen into the DNA of rapidly dividing cells. Upon exposure to UVA, it forms DNA cross-links (cyclobutane dimers), which inhibit DNA synthesis and suppress cellular proliferation. Additionally, PUVA induces apoptosis of T-lymphocytes, leading to local immunosuppression and clearing of psoriatic plaques. **2. Why other options are incorrect:** * **Tinea versicolor:** This is a superficial fungal infection caused by *Malassezia furfur*. It is treated with topical or systemic antifungals (e.g., Ketoconazole), not phototherapy. * **Lichen planus:** While Narrowband UVB (NBUVB) can be used for generalized lichen planus, PUVA is not the primary treatment. Furthermore, in the context of standard NEET-PG questions, Psoriasis remains the "gold standard" indication for PUVA. * **Porphyria cutanea tarda (PCT):** This is a metabolic disorder of heme synthesis. UV light actually *exacerbates* porphyrias (photosensitivity). Treatment involves phlebotomy or low-dose hydroxychloroquine. **Clinical Pearls for NEET-PG:** * **Wavelength:** UVA (320–400 nm); NBUVB (311–312 nm). NBUVB is now preferred over PUVA due to a lower risk of skin cancer. * **Side Effects:** Acute (erythema, pruritus, nausea) and Chronic (Photoaging, **Squamous Cell Carcinoma**, and "PUVA lentigines"). * **Other Indications:** Vitiligo, Mycosis Fungoides (CTCL), and Alopecia Areata. * **Contraindication:** Xeroderma pigmentosum, Systemic Lupus Erythematosus (SLE), and pregnancy.

Q: What is the most effective treatment for pruritus in uremia?

Ultraviolet light. **Explanation:** **Uremic pruritus** is a common and distressing complication of chronic kidney disease (CKD). While its exact pathogenesis is multifactorial—involving uremic toxins, systemic inflammation, and opioid receptor imbalances—**Ultraviolet (UV) light therapy**, specifically **Narrowband UVB (NB-UVB)**, is considered the most effective and first-line non-pharmacological treatment. * **Why Ultraviolet Light is Correct:** UV radiation (especially UVB) reduces the number of pro-inflammatory cytokines and mast cells in the skin. It also induces apoptosis of dermal mast cells and alters the cutaneous nerve endings, significantly reducing the itch sensation. It is highly effective in patients who do not respond to emollients or systemic antihistamines. **Analysis of Incorrect Options:** * **Cholestyramine (B):** This bile acid sequestrant is primarily used for pruritus associated with **cholestatic liver disease**. While it has been tried in uremia, its efficacy is inconsistent and inferior to phototherapy. * **Eskazine (C):** Also known as Trifluoperazine (an antipsychotic), it has no established role in treating uremic pruritus. * **Topical Benzocaine (D):** This is a local anesthetic. While it may provide transient numbing, it does not address the systemic cause of uremic itch and carries a high risk of **allergic contact dermatitis**. **High-Yield Clinical Pearls for NEET-PG:** 1. **First-line treatment:** Emollients and optimizing dialysis. 2. **Most effective/Gold standard:** NB-UVB phototherapy. 3. **Pharmacological options:** Gabapentin or Pregabalin (very effective, but requires dose adjustment for renal failure). 4. **Newer Drug:** **Difelikefalin** (a peripheral kappa-opioid receptor agonist) is now FDA-approved specifically for uremic pruritus. 5. **Key Association:** Uremic pruritus is often associated with secondary hyperparathyroidism and elevated calcium-phosphate product.

Q: A 6-year-old child born to consanguinity has pallor and intolerance to sunlight. His urine was exposed to Wood's light. Probable diagnosis is:

Gunther disease. ***Gunther disease*** - The combination of **pallor**, **intolerance to sunlight** (photosensitivity), **consanguinity**, and particularly the **red fluorescence of urine under Wood's light** (due to increased uroporphyrins and coproporphyrins) is highly characteristic of **congenital erythropoietic porphyria (CEP)**, also known as Gunther disease. - This is an **autosomal recessive** disorder of heme synthesis, leading to accumulation of porphyrin precursors. Affected individuals often have **erythrodontia** (reddish-brown discoloration of teeth), severe **anemia**, and **hemolysis**, alongside marked photosensitivity. *SLE* - **Systemic lupus erythematosus (SLE)** can cause **photosensitivity** and **pallor (due to anemia)**, but it is an autoimmune disease, not an inborn error of metabolism. - It does not typically present with red fluorescent urine under Wood's light, which is a specific finding for porphyrias. *Xeroderma pigmentosum* - This is a rare **autosomal recessive** genetic disorder characterized by extreme **photosensitivity** and a high risk of skin cancers due to a defect in DNA repair mechanisms. - While it causes severe photosensitivity, it does not involve abnormalities in porphyrin metabolism or lead to red fluorescent urine. *Bloom syndrome* - **Bloom syndrome** is a rare **autosomal recessive** genetic disorder characterized by **photosensitivity**, **short stature**, a **distinctive facial appearance**, and an increased risk of cancer. - It does not involve porphyrin metabolism or result in red fluorescent urine under Wood's light.

Q: Which of the following chemical is responsible for the skin condition given below:

Psoralen. ***Psoralen*** - **Psoralens (furocoumarins)** are the causative agents for **phytophotodermatitis** shown in the image - Found naturally in **citrus fruits (limes, lemons), celery, parsley, figs** and other plants - Mechanism: **Phototoxic reaction** when psoralen-containing plant material contacts skin followed by **UV light exposure** - Clinical features: **Linear or drip-pattern hyperpigmentation** corresponding to areas of plant juice contact, often with preceding erythema and blistering - This is the **classic presentation** seen with lime juice exposure ("margarita dermatitis") *Hydroquinone* - Used for **skin lightening** in melasma and hyperpigmentation disorders - Can cause **exogenous ochronosis** (blue-black pigmentation) with prolonged use - Does **not cause phototoxic reactions** with the linear pattern shown in the image - Side effects include irritant dermatitis, but not the characteristic distribution seen here *Monobenzyl ether of hydroquinone (MBEH)* - Permanent **depigmenting agent** used in extensive vitiligo - Causes **permanent destruction of melanocytes** leading to depigmentation - The image shows **hyperpigmentation**, not depigmentation, ruling this out - Can cause contact dermatitis but not phototoxic reactions *Para-tertiary butyl phenol (PTBP)* - Industrial chemical causing **leukoderma** (depigmentation) with occupational exposure - Historically found in **leather adhesives** and germicidal detergents - Causes **patchy depigmentation**, not the linear hyperpigmentation shown - Mechanism is melanocyte destruction, opposite to the clinical picture

Q: What is the best time to give oral psoralen with UVA -

1 hour before UVA. ***1 hour before UVA*** - Oral psoralen, when used in **PUVA therapy**, requires adequate time for absorption and distribution to the skin to exert its photosensitizing effects. - Administering psoralen approximately **1-2 hours before UVA exposure** (typically 1.5-2 hours for 8-methoxypsoralen) ensures peak drug concentration in the skin, maximizing therapeutic efficacy. - Among the given options, **1 hour is the most appropriate timing** as it allows sufficient absorption while being closer to the therapeutic window than shorter intervals. *Half an hour after UVA* - Administering psoralen **after UVA exposure** would mean the photosensitizer is not present in sufficient concentrations during the light therapy. - This timing would render the UVA treatment largely ineffective as the primary mechanism of action, **photoreaction with UVA**, would not occur. *1 hour after UVA* - Giving psoralen **1 hour after UVA** completely misses the therapeutic window needed for the drug to photosensitize the skin during light exposure. - The UVA light would have already been administered without the active drug in the skin, thus providing **minimal to no therapeutic benefit**. *Half hour before UVA* - **Half an hour before UVA** is insufficient time for adequate oral absorption and distribution of psoralen to achieve optimal photosensitization. - This could result in **suboptimal drug concentration at the time of UVA exposure** and reduced therapeutic efficacy compared to the standard 1-2 hour pre-treatment timing.

Question 1

A 45-year-old farmer presents with itchy erythematous papular lesions on the face, neck, 'V' area of the chest, and dorsum of hands and forearms, present for 3 years. The lesions are more severe in summers and improve in winters. What is the most appropriate diagnostic test for this condition?

Accepted Answer

Skin biopsy

Answer

Estimation of IgE levels in blood

Answer

Patch test

Answer

Intradermal prick test

Question 2

Which of the following tumors is not caused by PUVA therapy?

Accepted Answer

Cutaneous T-cell lymphoma

Answer

Melanoma

Answer

Basal cell carcinoma (BCC)

Answer

Squamous cell carcinoma (SCC)

Question 3

All are true regarding Polymorphous light eruption (PMLE), EXCEPT?

Accepted Answer

Face is always affected

Answer

Rash caused by sun exposure

Answer

Rash triggered by exposure to artificial ultraviolet (UV) light

Answer

Healing without scarring

Question 4

What is the treatment of choice for the cutaneous complications of porphyria?

Accepted Answer

Beta carotene

Answer

Intravenous dextrose

Answer

Intravenous haematin

Answer

Calamine

Question 5

Skin cancers develop due to sunlight exposure induced by which type of radiation?

Accepted Answer

UVB rays

Answer

UVA rays

Answer

UVD rays

Answer

UVC rays

Question 6

Which of the following skin conditions is treated with PUVA therapy?

Accepted Answer

Psoriasis

Answer

Tinea versicolor

Answer

Lichen planus

Answer

Porphyria cutanea tarda

Question 7

What is the most effective treatment for pruritus in uremia?

Accepted Answer

Ultraviolet light

Answer

Cholestyramine

Answer

Eskazine

Answer

Topical benzocaine

Question 8

A 6-year-old child born to consanguinity has pallor and intolerance to sunlight. His urine was exposed to Wood's light. Probable diagnosis is:

Accepted Answer

Gunther disease

Answer

SLE

Answer

Xeroderma pigmentosum

Answer

Bloom syndrome

Question 9

Which of the following chemical is responsible for the skin condition given below:

Accepted Answer

Psoralen

Answer

Hydroquinone

Answer

Monobenzyl ether of hydroquinone (MBEH)

Answer

Para-tertiary butyl phenol (PTBP)

Question 10

What is the best time to give oral psoralen with UVA -

Accepted Answer

1 hour before UVA

Answer

Half an hour after UVA

Answer

1 hour after UVA

Answer

Half hour before UVA

Phototherapy and Photobiology — MCQs

Phototherapy and Photobiology — MCQs

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