Phototherapy and Photobiology — MCQs

A 45-year-old woman with poorly controlled type 2 diabetes (HbA1c 9.2%) and chronic kidney disease presents with intensely pruritic nodules on extensor surfaces for 8 months. Previous treatments with topical steroids, antihistamines, and gabapentin provided minimal relief. Skin biopsy shows acanthosis, compact orthokeratosis, and increased nerve fibers. CBC shows eosinophilia. Most appropriate next step is:

Q29

A 45-year-old male with hepatitis C presents with photosensitivity, blisters, and hypertrichosis. Laboratory results show increased serum porphyrins. What is the likely diagnosis?

Q30

A 30-year-old woman presents with blistering on her hands after sun exposure. She has a history of alcohol use disorder. Laboratory tests show elevated liver enzymes and low serum haptoglobin. Analyze the clinical scenario to identify the most likely diagnosis.

Phototherapy and Photobiology Indian Medical PG Practice Questions and MCQs

Question 21: PUVA therapy is used in all except:

A. Psoriasis
B. Vitiligo
C. Mycosis fungoides
D. Melasma (Correct Answer)

Explanation: ***Melasma*** - **PUVA (Psoralen plus UVA) therapy** is contraindicated in melasma due to its potential to worsen hyperpigmentation and cause paradoxical darkening. - Melasma is best managed with topical agents like **hydroquinone**, **tretinoin**, and chemical peels, along with strict **sun protection**. *Psoriasis* - **PUVA therapy** is a well-established and effective treatment for moderate to severe psoriasis, especially for patients with widespread plaques. - It works by inhibiting DNA synthesis and cell proliferation in rapidly dividing keratinocytes, leading to a reduction in psoriatic lesions. *Vitiligo* - **PUVA therapy** is a common treatment for vitiligo, stimulating melanocyte activity and promoting repigmentation in affected areas. - Psoralen sensitizes melanocytes to UVA light, which then encourages melanin production. *Mycosis fungoides* - In its early stages, **mycosis fungoides**, a cutaneous T-cell lymphoma, can be effectively treated with **PUVA therapy**. - PUVA induces apoptosis of malignant T-cells in the skin, leading to remission of skin lesions.

Question 22: 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 23: Wood's lamp has a wavelength of –

A. 320 nm
B. 300 nm
C. 360 nm (Correct Answer)
D. 250 nm

Explanation: ***360 nm*** - A **Wood's lamp** emits **long-wave ultraviolet (UV-A) light**, which is typically in the range of 320 to 450 nm. - The precise wavelength of **360 nm** is the most common and effective for dermatological diagnostic applications, allowing visualization of specific fluorescence patterns. *320 nm* - While 320 nm falls within the UV-A spectrum, it is at the lower end and less characteristic of the peak emission wavelength used in Wood's lamps for diagnostic purposes. - Using this lower wavelength might result in less pronounced or absent fluorescence for some conditions. *300 nm* - A wavelength of 300 nm is in the **UV-B spectrum** which is primarily used for therapeutic purposes like **phototherapy for psoriasis**, not for diagnostic fluorescence with a Wood's lamp. - UV-B light has different biological effects and is too short to elicit the characteristic fluorescence observed with a Wood's lamp. *250 nm* - This wavelength falls into the **UV-C spectrum**, which is **germicidal** and harmful to human tissue. - UV-C light is not used in Wood's lamps for diagnostic purposes due to its damaging properties and inability to produce the desired fluorescence.

Question 24: 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 25: Most common acute skin manifestation of radiotherapy:

A. Dermatitis
B. Erythema (Correct Answer)
C. Atopy
D. Hyperpigmentation

Explanation: ***Erythema*** - **Erythema** (redness) is the most immediate and common acute cutaneous reaction to radiotherapy due to **vasodilation** and inflammation of the skin in the irradiated area. - It often appears within days to weeks of starting radiation treatment and is a direct consequence of cell damage and the body's inflammatory response to it. *Dermatitis* - While radiation dermatitis is a broader term encompassing various skin changes from radiotherapy, **erythema** is the initial and most prevalent component of this dermatological spectrum, making it a more specific answer for the "most common" manifestation. - Dermatitis can also include later-stage problems like **dry desquamation** and **moist desquamation**, which are more severe reactions. *Atopy* - **Atopy** refers to a genetic predisposition to develop allergic diseases like asthma, allergic rhinitis, or atopic dermatitis. - It is an **intrinsic immune predisposition** and not a direct skin manifestation caused by radiotherapy itself. *Hyperpigmentation* - While **hyperpigmentation** can occur in the irradiated area, it is typically a **subacute or chronic** reaction, often appearing weeks to months after the onset of erythema or after the completion of treatment. - It is not the most immediate or common acute manifestation compared to erythema.

Question 26: Methoxysalen is used as:

A. Photoprotective agent
B. Used in photochemotherapy (Correct Answer)
C. Melanising agent
D. Depigmenting agent

Explanation: ***Used in photochemotherapy*** - **Methoxysalen** is a **psoralen derivative** that becomes activated by ultraviolet A (UVA) light. - This activation allows it to form **photoadducts with DNA**, inhibiting cell proliferation, which is the basis for its use in **photochemotherapy** for conditions like psoriasis and vitiligo. *Photoprotective agent* - **Photoprotective agents** like sunscreens work by **reflecting or absorbing UV radiation** to prevent skin damage. - **Methoxysalen** actually **sensitizes the skin to UV light**, increasing its effects rather than blocking them. *Melanising agent* - While methoxysalen can induce repigmentation in conditions like vitiligo, it does so by increasing the skin's sensitivity to UV light, which then stimulates **melanogenesis**. - It is not a direct melanising agent that independently promotes melanin production without UV exposure. *Depigmenting agent* - **Depigmenting agents** aim to reduce or remove melanin from the skin, often used for hyperpigmentation disorders. - **Methoxysalen**, especially when used in PUVA therapy, helps to **re-pigment** areas affected by conditions like vitiligo, making it the opposite of a depigmenting agent.

Question 27: A patient develops localized blisters after UV exposure. Which porphyria is most likely?

A. Acute intermittent porphyria
B. Porphyria cutanea tarda (Correct Answer)
C. Erythropoietic protoporphyria
D. Congenital erythropoietic porphyria

Explanation: ***Porphyria cutanea tarda*** - This is the **most common porphyria** and is classically characterized by **photosensitivity** leading to **vesicles and bullae** (blisters), skin fragility, and hyperpigmentation in sun-exposed areas (particularly dorsum of hands). - The localized blisters after UV exposure are a hallmark sign, resulting from the accumulation of **uroporphyrins** in the skin, which are activated by UV light (400-410 nm wavelength). - Associated with hepatic dysfunction, alcohol use, hepatitis C, estrogen use, and hemochromatosis. *Acute intermittent porphyria* - Primarily causes **neurovisceral symptoms** such as acute abdominal pain, psychiatric disturbances, and neurological deficits. - It typically **does not present with cutaneous manifestations** or photosensitivity. - This is a hepatic porphyria without skin involvement. *Erythropoietic protoporphyria* - Characterized by **immediate painful photosensitivity** that manifests as burning, stinging, and itching within minutes of sun exposure. - Presents with **erythema and edema** but typically **no vesicles or bullae** - this is the key differentiating feature from PCT. - Patients experience acute pain and may develop petechiae, but distinct localized blisters are not characteristic. - Long-term exposure can lead to waxy scarring and thickened skin. *Congenital erythropoietic porphyria* - Also known as **Günther's disease**, this is a very rare and severe porphyria presenting in infancy or early childhood. - It causes severe photosensitivity with **vesicles, bullae, and mutilating scarring**, as well as **hemolytic anemia** and **reddish urine and teeth (erythrodontia)**. - The early onset, severity, and systemic features distinguish it from PCT in adults.

Question 28: A 45-year-old woman with poorly controlled type 2 diabetes (HbA1c 9.2%) and chronic kidney disease presents with intensely pruritic nodules on extensor surfaces for 8 months. Previous treatments with topical steroids, antihistamines, and gabapentin provided minimal relief. Skin biopsy shows acanthosis, compact orthokeratosis, and increased nerve fibers. CBC shows eosinophilia. Most appropriate next step is:

A. Initiate dupilumab (Correct Answer)
B. Begin phototherapy
C. Start oral cyclosporine
D. Trial of oral doxepin

Explanation: ***Initiate dupilumab*** - **Dupilumab** was FDA-approved for **prurigo nodularis** in September 2022 and is now considered **first-line systemic therapy** for moderate-to-severe cases refractory to topical treatments. - Phase 3 trials (PRIME, PRIME2) demonstrated **significant improvement in pruritus** (>50% reduction in itch scores) and **lesion clearance** in patients with prurigo nodularis. - **Excellent safety profile** in patients with **chronic kidney disease** and **diabetes** - no dose adjustment needed for CKD, and does not worsen glycemic control or renal function. - As a **targeted biologic** (IL-4/IL-13 inhibitor), it addresses the underlying type 2 inflammation in prurigo nodularis with minimal systemic adverse effects. - Given this patient's **failure of multiple prior therapies** and **severe comorbidities**, dupilumab is the most appropriate next step. *Incorrect: Begin phototherapy* - While **narrowband UVB phototherapy** is effective for prurigo nodularis, it is typically considered **second-line or adjunctive therapy** rather than first-line systemic treatment for severe refractory cases. - Requires **multiple weekly visits** (2-3 times per week initially), which may be challenging for patients with significant comorbidities. - In the current era with FDA-approved biologics for prurigo nodularis, phototherapy is often reserved for patients who cannot access or have failed biologic therapy. *Incorrect: Start oral cyclosporine* - Oral cyclosporine carries significant risks of **nephrotoxicity** and **hyperglycemia**, which would be especially problematic in a patient with pre-existing **chronic kidney disease** and **poorly controlled diabetes** (HbA1c 9.2%). - While it can be effective for severe prurigo nodularis, the risk-benefit ratio is unfavorable in this clinical context given safer alternatives. - Requires frequent monitoring of renal function and blood pressure. *Incorrect: Trial of oral doxepin* - Oral doxepin, a **tricyclic antidepressant with H1/H2 antihistaminic properties**, can help with chronic pruritus but is typically less effective for **nodular lesions**. - Causes significant **sedation** and anticholinergic side effects, which may not be well-tolerated. - Given that standard antihistamines and gabapentin have already failed, and considering the **severity and chronicity** of symptoms (8 months, intensely pruritic nodules), a more potent targeted therapy is warranted.

Question 29: A 45-year-old male with hepatitis C presents with photosensitivity, blisters, and hypertrichosis. Laboratory results show increased serum porphyrins. What is the likely diagnosis?

A. Porphyria cutanea tarda; phlebotomy + hydroxychloroquine (Correct Answer)
B. Polycythemia vera; high-dose steroids
C. Lichen planus; topical steroids, oral retinoids
D. Dermatitis herpetiformis; gluten-free diet + dapsone

Explanation: ***Porphyria cutanea tarda; phlebotomy + hydroxychloroquine*** - **Porphyria cutanea tarda (PCT)** is strongly suggested by the triad of **photosensitivity**, **blisters**, and **hypertrichosis**, especially in a patient with **hepatitis C**. - **Increased serum porphyrins** confirm the diagnosis, and **phlebotomy** (to reduce iron overload) and **hydroxychloroquine** (to reduce porphyrin accumulation) are established treatments. *Polycythemia vera; high-dose steroids* - **Polycythemia vera** is a myeloproliferative disorder characterized by an overproduction of red blood cells, not skin lesions, photosensitivity, or increased porphyrins. - **High-dose steroids** are not a primary treatment for polycythemia vera; **phlebotomy** and **hydroxyurea** are common therapies. *Lichen planus; topical steroids, oral retinoids* - **Lichen planus** presents with **pruritic, purple, polygonal papules** often on the wrists, ankles, and oral mucosa, which does not match the described symptoms. - While **topical steroids** are used for lichen planus, it does not involve photosensitivity, blisters, or abnormal porphyrin levels. *Dermatitis herpetiformis; gluten-free diet + dapsone* - **Dermatitis herpetiformis** typically presents as intensely **pruritic vesicles and bullae** on extensor surfaces, strongly associated with **celiac disease**. - There is no mention of gut symptoms or an association with hepatitis C, and the primary treatment involves a **gluten-free diet** and **dapsone**.

Question 30: A 30-year-old woman presents with blistering on her hands after sun exposure. She has a history of alcohol use disorder. Laboratory tests show elevated liver enzymes and low serum haptoglobin. Analyze the clinical scenario to identify the most likely diagnosis.

A. Porphyria cutanea tarda (Correct Answer)
B. Pemphigus vulgaris (PV)
C. Dermatitis herpetiformis (DH)
D. Systemic lupus erythematosus (SLE)

Explanation: ***Porphyria cutanea tarda*** - **Blistering on sun-exposed areas** (hands) and a history of **alcohol use disorder** are classic presentations of PCT. - **Elevated liver enzymes** support the diagnosis, as PCT is strongly associated with liver disease, alcohol use, hepatitis C, and iron overload. - PCT is the most common porphyria and results from deficiency of uroporphyrinogen decarboxylase (UROD), leading to accumulation of photosensitizing porphyrins in the skin. *Pemphigus vulgaris (PV)* - Presents with **flaccid blisters** and erosions primarily affecting the **mucous membranes** and skin, often without a strong association with sun exposure. - Diagnosis is confirmed by **direct immunofluorescence** showing anti-desmoglein antibodies, and generally not associated with liver enzyme abnormalities or alcohol use. *Dermatitis herpetiformis (DH)* - Characterized by **intensely pruritic vesicles** and papules, mainly on extensor surfaces (elbows, knees, buttocks), strongly associated with **celiac disease** and gluten sensitivity. - While it is a blistering disease, sun exposure is not a primary trigger, nor are liver enzyme abnormalities or alcohol use typical associations. *Systemic lupus erythematosus (SLE)* - Photosensitivity can cause skin lesions, but typically presents as a **malar rash** or discoid lesions, not vesiculobullous eruptions. - It is a systemic autoimmune disease with diverse manifestations, but **blistering due to sun exposure** as the primary finding is not characteristic of SLE.

Practice by Chapter

Fundamentals of Photobiology

Practice Questions

UVA and UVB Phototherapy

Practice Questions

PUVA Therapy

Practice Questions

Narrow-Band UVB Therapy

Practice Questions

Excimer Laser Therapy

Practice Questions

Photodynamic Therapy

Practice Questions

Phototoxicity and Photoallergy

Practice Questions

Photoprotection

Practice Questions

Sunscreens

Practice Questions

Photoaging

Practice Questions

Phototherapy Protocols

Practice Questions

Management of Phototherapy Side Effects

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free