Phototherapy and Photobiology Practice Questions

Q: PUVA therapy is used in all except:

Melasma. ***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.

Q: A sunscreen ointment has a Sun-Protection-Factor (SPF) of 15. How much UV radiation does it filter out?

93%. ***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%.

Q: Wood's lamp has a wavelength of –

360 nm. ***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.

Q: What is the best range of UV light used for treatment of skin diseases?

200 – 400 nm. ***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.

Q: PUVA therapy is used in:

Psoriasis. ***Psoriasis*** - **PUVA (Psoralen plus ultraviolet A)** therapy is a well-established and effective treatment for **moderate-to-severe psoriasis**. - Psoralen is a photosensitizing agent that, when activated by UVA light, inhibits **DNA synthesis** and reduces cell proliferation in the affected skin. - PUVA is considered a **gold standard phototherapy** for psoriasis, particularly for extensive plaque psoriasis and generalized disease. *Melasma* - Melasma is a **hyperpigmentary disorder** characterized by dark patches on the face. - While some light-based therapies are used, **topical agents** like hydroquinone and chemical peels are the primary treatments, and PUVA is not typically indicated due to the risk of worsening hyperpigmentation. *Lichen planus* - Lichen planus is an **inflammatory skin condition** that can be treated with phototherapy including **PUVA**, particularly for oral lichen planus and widespread cutaneous disease. - However, **narrowband UVB** is generally preferred as first-line phototherapy due to fewer side effects. - While PUVA has a role in lichen planus, psoriasis remains the **primary and most established indication** for this therapy. *Freckles* - Freckles are **benign pigmented macules** and do not require medical treatment. - Protection from **UV exposure** and cosmetic treatments like laser therapy for aesthetic reasons are sometimes used, but PUVA is entirely inappropriate and would cause harm.

Q: Methoxysalen is used as:

Used in photochemotherapy. ***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.

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

Porphyria cutanea tarda. ***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.

Q: How does narrowband UVB therapy work in psoriasis?

T cell apoptosis. ***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.

Q: 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?

Porphyria cutanea tarda; phlebotomy + hydroxychloroquine. ***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**.

Q: A 50-year-old male with a history of liver disease presents with a photosensitive, blistering rash on his hands. What is the most likely diagnosis?

Porphyria cutanea tarda. ***Porphyria cutanea tarda*** - The classic triad of **photosensitive blistering on sun-exposed areas** (especially dorsal hands), **fragile skin**, and **association with liver disease** makes PCT the most likely diagnosis. - Caused by deficiency of **uroporphyrinogen decarboxylase**, leading to accumulation of photoreactive porphyrins in the skin. - Strong associations include **hepatitis C, alcohol-related liver disease, hemochromatosis**, and estrogen use. - Characteristic findings: vesicles, bullae, erosions, milia, and hyperpigmentation on sun-exposed areas. *Herpes simplex* - Presents as **grouped vesicles on an erythematous base**, often with prodrome of tingling or burning. - Not characteristically photosensitive and **no association with liver disease**. - Lesions are typically recurrent in the same location and resolve with crusting. *Bullous pemphigoid* - An **autoimmune subepidermal blistering disease** with tense bullae and intense pruritus. - Typically affects elderly patients but **not associated with photosensitivity or liver disease**. - Blisters can occur on any body site, not specifically sun-exposed areas. *Pemphigus vulgaris* - An **autoimmune intraepidermal blistering disease** with flaccid bullae that easily rupture, leaving painful erosions. - Often involves **mucous membranes** (oral cavity most common). - **No association with photosensitivity or liver disease**.

Question 1

PUVA therapy is used in all except:

Accepted Answer

Melasma

Answer

Psoriasis

Answer

Vitiligo

Answer

Mycosis fungoides

Question 2

A sunscreen ointment has a Sun-Protection-Factor (SPF) of 15. How much UV radiation does it filter out?

Accepted Answer

93%

Answer

15%

Answer

98%

Answer

85%

Question 3

Wood's lamp has a wavelength of –

Accepted Answer

360 nm

Answer

320 nm

Answer

300 nm

Answer

250 nm

Question 4

What is the best range of UV light used for treatment of skin diseases?

Accepted Answer

200 – 400 nm

Answer

100 – 200 nm

Answer

> 700 nm

Answer

400 – 700 nm

Question 5

PUVA therapy is used in:

Accepted Answer

Psoriasis

Answer

Melasma

Answer

Lichen planus

Answer

Freckles

Question 6

Methoxysalen is used as:

Accepted Answer

Used in photochemotherapy

Answer

Photoprotective agent

Answer

Melanising agent

Answer

Depigmenting agent

Question 7

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

Accepted Answer

Porphyria cutanea tarda

Answer

Acute intermittent porphyria

Answer

Erythropoietic protoporphyria

Answer

Congenital erythropoietic porphyria

Question 8

How does narrowband UVB therapy work in psoriasis?

Accepted Answer

T cell apoptosis

Answer

Melanin synthesis

Answer

Collagen breakdown

Answer

Keratinocyte proliferation

Question 9

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?

Accepted Answer

Porphyria cutanea tarda; phlebotomy + hydroxychloroquine

Answer

Polycythemia vera; high-dose steroids

Answer

Lichen planus; topical steroids, oral retinoids

Answer

Dermatitis herpetiformis; gluten-free diet + dapsone

Question 10

A 50-year-old male with a history of liver disease presents with a photosensitive, blistering rash on his hands. What is the most likely diagnosis?

Accepted Answer

Porphyria cutanea tarda

Answer

Herpes simplex

Answer

Bullous pemphigoid

Answer

Pemphigus vulgaris

Phototherapy and Photobiology — MCQs

Phototherapy and Photobiology — MCQs

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