Phototoxicity and Photoallergy — MCQs
A 26-year-old pregnant woman presents with arthritis and a malar rash that worsens with sun exposure. She has a low-grade fever and is admitted to the hospital. What is the likely diagnosis?
A child with history of fever, photosensitivity, rash sparing nasolabial fold presents to OP. Identify the condition?
Lady presents with joint pain in both knees and low-grade fever, which occurs intermittently. On examination, she has a rash on sun-exposed areas. What is the clinical diagnosis?
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?
What is the range of light that causes maximum skin damage?
Phototoxicity and Photoallergy Indian Medical PG Practice Questions and MCQs
Question 1: A 26-year-old pregnant woman presents with arthritis and a malar rash that worsens with sun exposure. She has a low-grade fever and is admitted to the hospital. What is the likely diagnosis?
- A. Lyme disease
- B. Chloasma
- C. Systemic Lupus Erythematosus (Correct Answer)
- D. Steven Johnsons syndrome
Explanation: ***Systemic Lupus Erythematosus*** - The combination of **arthritis**, **malar rash** that worsens with sun exposure (photosensitivity), and a **low-grade fever** in a young woman is highly characteristic of systemic lupus erythematosus (SLE) [1]. - SLE is an **autoimmune disease** with diverse clinical manifestations affecting multiple organ systems [1]. *Lyme disease* - Characterized by a **target-like rash (erythema migrans)**, which is distinct from a malar rash, and often presents with flu-like symptoms. - While Lyme disease can cause arthritis, the presence of a classic malar rash and photosensitivity points away from this diagnosis. *Chloasma* - Also known as the **"mask of pregnancy,"** chloasma is a common skin condition in pregnant women causing dark, discolored patches on the face. - It is a **pigmentation disorder** and does not involve arthritis, fever, or an associated malar rash that worsens with sun exposure. *Steven Johnsons syndrome* - An infrequent, serious systemic reaction to medication or infection, that triggers severe skin and mucous membrane reactions, typically presenting with **widespread blistering** and epidermal detachment. - This is an **acute, severe mucocutaneous reaction** and does not present with the chronic arthritis and photosensitive malar rash seen in this patient.
Question 2: A child with history of fever, photosensitivity, rash sparing nasolabial fold presents to OP. Identify the condition?
- A. SLE (Correct Answer)
- B. Polymorphous light eruption
- C. Discoid lupus
- D. Skin tuberculosis
Explanation: ***SLE*** - The combination of **fever**, **photosensitivity**, and a **rash sparing the nasolabial folds** (malar rash or butterfly rash) is highly characteristic of Systemic Lupus Erythematosus (SLE). - Childhood-onset SLE can present with similar mucocutaneous and systemic features as adult-onset disease. *Polymorphous light eruption* - This condition is primarily characterized by **photosensitive skin lesions** but typically does not involve systemic symptoms like fever. - While it presents with rash in sun-exposed areas, it generally lacks the distinct malar rash appearance and systemic involvement seen in SLE. *Discoid lupus* - Discoid lupus is a form of **cutaneous lupus** characterized by chronic, scaly, disfiguring plaques, often on the face and scalp. - It usually **lacks systemic symptoms** like fever and does not present as a widespread malar rash sparing nasal folds. *Skin tuberculosis* - Skin tuberculosis (lupus vulgaris or scrofuloderma) presents with **nodular, plaque-like lesions** or cold abscesses, often with ulceration and scarring. - It is not typically associated with **photosensitivity** or a malar rash, and fever, if present, is usually due to systemic Mycobacterium infection.
Question 3: Lady presents with joint pain in both knees and low-grade fever, which occurs intermittently. On examination, she has a rash on sun-exposed areas. What is the clinical diagnosis?
- A. Systemic lupus erythematosus (SLE) (Correct Answer)
- B. Rheumatoid arthritis (RA)
- C. Photodermatitis
- D. Porphyria cutanea tarda
Explanation: ***Systemic lupus erythematosus (SLE)*** - The combination of **polyarthralgia (joint pain)**, **low-grade fever**, and a **photosensitive rash** is highly characteristic of SLE. [1] - SLE is a **multisystem autoimmune disease** that can affect joints, skin, and cause constitutional symptoms like fever. [1] *Rheumatoid arthritis (RA)* - While RA causes **joint pain**, it typically presents with **symmetrical polyarthritis** primarily affecting small joints, and a photosensitive rash is not a common feature. [2] - **Fever** can be present in severe RA, but the triad of symptoms in this case points away from RA as the primary diagnosis. *Photodermatitis* - **Photodermatitis** is a skin inflammation caused by sunlight exposure, resulting in a rash. - This diagnosis does not account for the **joint pain** or **low-grade fever**, which are systemic manifestations. *Porphyria cutanea tarda* - This condition primarily affects the skin, causing **photosensitivity**, blistering lesions, and increased fragility, especially on sun-exposed areas. - It does **not typically present with joint pain or fever**, differentiating it from the presented symptoms.
Question 4: 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 5: 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 6: 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 7: 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 8: 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 9: 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.
Question 10: What is the range of light that causes maximum skin damage?
- A. 360-400 nm
- B. 290-360 nm (Correct Answer)
- C. 240-290 nm
- D. 760-800 nm
Explanation: **Explanation:** The spectrum of light responsible for the majority of skin damage encompasses **Ultraviolet B (UVB: 290–320 nm)** and **Ultraviolet A (UVA: 320–400 nm)**. The range **290–360 nm** is the most clinically significant because it includes the entirety of UVB—the most erythemogenic and carcinogenic wavelengths—and the "short-wave" UVA (UVA2) portion. * **UVB (290–320 nm):** Known as the "burning rays," these have high energy and are primarily responsible for DNA damage (pyrimidine dimers), sunburn (erythema), and skin cancers (BCC, SCC, and Melanoma). * **UVA (320–400 nm):** Known as "aging rays," these penetrate deeper into the dermis, causing photoaging and indirect DNA damage via reactive oxygen species (ROS). **Analysis of Incorrect Options:** * **A (360–400 nm):** This is UVA1 (long-wave UVA). While it contributes to photoaging and tanning, it is significantly less potent in causing acute biological damage or DNA mutations compared to the 290–360 nm range. * **C (240–290 nm):** This falls within the UVC range. While highly energetic and dangerous, UVC is almost entirely absorbed by the Earth’s ozone layer and does not reach the skin under normal conditions. * **D (760–800 nm):** This is part of the Near-Infrared/Visible light spectrum. These wavelengths primarily produce heat and do not possess enough energy to cause direct photochemical DNA damage. **High-Yield Clinical Pearls for NEET-PG:** * **Minimal Erythema Dose (MED):** The smallest dose of UV radiation that produces confluent erythema at 24 hours. It is used to calibrate phototherapy. * **Action Spectrum:** The specific wavelength of light that produces a particular biological response (e.g., 290–300 nm is the peak for erythema). * **Narrowband UVB (NBUVB):** 311–313 nm. This is the "Gold Standard" for treating Psoriasis and Vitiligo as it maximizes therapeutic effect while minimizing burning.
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