Sunscreens — MCQs
What is the best range of UV light used for treatment of skin diseases?
How does narrowband UVB therapy work in psoriasis?
A patient presents with a skin rash that is exaggerated on sun exposure. What is the repair mechanism involved in this condition?
A sunscreen ointment has a Sun-Protection-Factor (SPF) of 15. How much UV radiation does it filter out?
Which of the following is NOT a complication of PUVA therapy?
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?
Psoralen plus ultraviolet A (PUVA) therapy is useful in which of the following conditions?
Psoralen is used in the treatment of:
All of the following are true about solar urticaria EXCEPT:
What is the wavelength range of UVB rays?
Sunscreens Indian Medical PG Practice Questions and MCQs
Question 1: What is the best range of UV light used for treatment of skin diseases?
- A. 100 – 200 nm
- B. > 700 nm
- C. 400 – 700 nm
- D. 200 – 400 nm (Correct Answer)
Explanation: ***200 – 400 nm*** - This range encompasses **UVA (320-400 nm)** and **UVB (290-320 nm)**, which are the most commonly used portions of the **UV spectrum** for treating various skin conditions like psoriasis and eczema. - Specifically, **narrowband UVB (311-313 nm)** is highly effective due to its therapeutic benefits with reduced side effects compared to broadband UVB or UVA. *100 – 200 nm* - This range falls into the **vacuum UV (VUV)** spectrum, which is largely absorbed by air and is not practical for dermatological phototherapy due to its limited penetration and potential for significant cellular damage. - It is known for its germicidal properties but is not used for treating skin diseases in living tissue due to its **high energy** and **low penetration** depth. *> 700 nm* - Wavelengths above 700 nm fall into the **infrared (IR) spectrum** or visible light, which primarily produces heat and has different therapeutic applications. - While IR light can be used for therapies like **pain relief** and **wound healing**, it does not have the immunomodulatory effects on skin cells needed for conditions traditionally treated by UV. *400 – 700 nm* - This range represents the **visible light spectrum**, which is used in some dermatological treatments like **photodynamic therapy (PDT)** or for certain **pigmentary disorders**. - However, visible light does not possess the same **immunomodulatory** and **antiproliferative effects** on keratinocytes and T-cells that make UV light effective for conditions like psoriasis.
Question 2: How does narrowband UVB therapy work in psoriasis?
- A. Melanin synthesis
- B. Collagen breakdown
- C. Keratinocyte proliferation
- D. T cell apoptosis (Correct Answer)
Explanation: ***T cell apoptosis*** - Narrowband UVB (NB-UVB) therapy primarily works by inducing **apoptosis (programmed cell death)** of activated **T-lymphocytes** in the psoriatic skin lesions. - By reducing the number of these inflammatory cells, NB-UVB helps to suppress the immune response that drives the **excessive keratinocyte proliferation** in psoriasis. *Melanin synthesis* - While UV radiation does stimulate **melanin synthesis**, leading to tanning, this is a secondary effect and not the primary therapeutic mechanism for psoriasis. - Increased melanin helps protect the skin from UV damage but does not directly treat the underlying pathology of psoriasis. *Collagen breakdown* - UV radiation, especially UVA, can contribute to **collagen breakdown** and photodamage over time, but this is an adverse effect, not a therapeutic mechanism for psoriasis. - Psoriasis treatment aims to normalize skin cell growth and reduce inflammation, not degrade collagen. *Keratinocyte proliferation* - Psoriasis is characterized by **accelerated keratinocyte proliferation**; NB-UVB therapy aims to *reduce* this proliferation, not promote it. - The mechanism by which NB-UVB achieves this reduction is primarily through its effects on immune cells, not by directly enhancing keratinocyte growth.
Question 3: A patient presents with a skin rash that is exaggerated on sun exposure. What is the repair mechanism involved in this condition?
- A. Nucleotide excision repair (Correct Answer)
- B. Base excision repair
- C. Mismatch repair
- D. Double stranded DNA break repair
Explanation: ***Nucleotide excision repair*** - This mechanism is responsible for repairing **bulky lesions** in DNA, such as **pyrimidine dimers** caused by **UV radiation** from sun exposure. - Patients with defects in nucleotide excision repair (e.g., **xeroderma pigmentosum**) are highly sensitive to sunlight and develop skin rashes, pigment changes, and skin cancers. *Base excision repair* - This pathway primarily corrects **small damaged bases** that do not cause significant distortion of the DNA helix, such as deaminated, oxidized, or alkylated bases. - It does not primarily address the bulky lesions induced by UV light that cause exaggerated sun sensitivity. *Mismatch repair* - This system corrects errors, like **mismatched base pairs**, that are incorporated during DNA replication. - It is not directly involved in repairing DNA damage caused by environmental factors like UV radiation. *Double stranded DNA break repair* - This mechanism repairs **double-strand breaks** in DNA, which are highly deleterious lesions caused by ionizing radiation or oxidative stress. - While critical for genome stability, it is not the primary repair pathway for UV-induced DNA lesions or the direct cause of sun sensitivity.
Question 4: A sunscreen ointment has a Sun-Protection-Factor (SPF) of 15. How much UV radiation does it filter out?
- A. 15%
- B. 98%
- C. 85%
- D. 93% (Correct Answer)
Explanation: ***93%*** - An **SPF of 15** signifies that approximately **93% of UVB radiation** is filtered out by the sunscreen. - The formula to calculate the percentage of UV radiation blocked is **(1 - 1/SPF) × 100**. - For SPF 15: (1 - 1/15) × 100 = 93.33% ≈ 93% *15%* - This percentage is much too low for an SPF 15 sunscreen; it would mean the sunscreen is largely ineffective. - SPF 15 indicates a significant reduction, not just 15%, of UV radiation reaching the skin. *98%* - An **SPF of 50** typically blocks approximately 98% of UV radiation, not SPF 15. - This percentage implies a much higher level of protection than what an SPF 15 sunscreen offers. *85%* - This percentage of UV blockage is generally associated with a lower SPF value, approximately **SPF 6-7**. - An SPF of 15 provides a higher level of protection than 85%.
Question 5: 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 6: 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 7: 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 8: 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 9: All of the following are true about solar urticaria EXCEPT:
- A. Common in females between the age group of 20-40 years. (Correct Answer)
- B. Lesions subside spontaneously on avoiding exposure within 24 hours.
- C. Some cases may develop severe urticaria or bronchospasm.
- D. Almost all cases are idiopathic.
Explanation: **Explanation:** Solar urticaria is a rare, IgE-mediated physical urticaria triggered by exposure to ultraviolet (UV) or visible light. **1. Why Option A is the correct answer (The Exception):** While solar urticaria can occur at any age, the peak incidence is actually in the **younger age group (median age of onset is 35 years)**, but it shows **no significant gender predilection**. Unlike other autoimmune conditions, it does not predominantly favor females in the 20-40 age bracket. Therefore, stating it is "common in females" specifically is inaccurate in the context of clinical epidemiology. **2. Analysis of other options:** * **Option B:** Characteristically, the wheals appear within minutes of sun exposure and **subside spontaneously within 1 to 24 hours** once the patient moves into the shade, leaving no residual scarring. * **Option C:** If a large surface area of the body is exposed, massive histamine release can lead to systemic symptoms, including **faintness, bronchospasm, or even anaphylaxis**. * **Option D:** The majority of cases are **idiopathic**. It is hypothesized to be a Type I hypersensitivity reaction to an endogenous "photo-allergen" created by light exposure. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Confirmed by **Phototesting** (determining the Minimal Urticarial Dose). * **Action Spectrum:** Most commonly triggered by **UVA** and visible light. * **Treatment:** First-line treatment is **H1 antihistamines**. For refractory cases, **PUVA (photodesensitization)** or Omalizumab may be used. * **Differential:** Differentiate from Polymorphous Light Eruption (PMLE), where lesions take hours/days to appear and days to resolve.
Question 10: 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.
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