Phototherapy and Photobiology Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Phototherapy and Photobiology. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Phototherapy and Photobiology Indian Medical PG Question 1: What is the primary condition for which calcitriol is used as a treatment?
- A. Pemphigus
- B. Secondary hyperparathyroidism (Correct Answer)
- C. Lichen planus
- D. Leprosy
Phototherapy and Photobiology Explanation: Secondary hyperparathyroidism
- Calcitriol is the active form of vitamin D (1,25-dihydroxyvitamin D₃), and it is crucial for regulating calcium and phosphate levels in the body [1].
- In secondary hyperparathyroidism, often seen in chronic kidney disease (CKD), the kidneys cannot convert vitamin D to its active form, leading to hypocalcemia and increased PTH secretion [1], [2].
- Calcitriol supplementation helps to increase calcium absorption from the gut and suppress the release of parathyroid hormone (PTH), thereby treating the underlying cause of secondary hyperparathyroidism [1], [2].
- This is the primary therapeutic indication for calcitriol in clinical practice.
Lichen planus
- This is a chronic inflammatory condition affecting the skin, hair, nails, and mucous membranes
- Typically treated with corticosteroids or other immunosuppressants
- Calcitriol has no primary role in the treatment of lichen planus; its therapeutic applications are predominantly related to calcium and bone metabolism
Pemphigus
- Pemphigus is a group of rare autoimmune blistering diseases that affect the skin and mucous membranes
- Primary treatment involves immunosuppressants like corticosteroids, often in high doses
- Calcitriol is not indicated for the treatment of pemphigus, as its mechanism of action is unrelated to the autoimmune processes characteristic of this disease
Leprosy
- Leprosy is a chronic infectious disease caused by the bacterium Mycobacterium leprae
- Treated with multi-drug therapy (MDT), which includes antibiotics like rifampicin, dapsone, and clofazimine
- Calcitriol is not an antibiotic and therefore has no role in treating the bacterial infection responsible for leprosy
Phototherapy and Photobiology Indian Medical PG Question 2: What is the repair mechanism associated with CRISPR-cas9?
- A. Mismatch repair
- B. Non-homologous end joining (Correct Answer)
- C. Nucleotide excision repair
- D. Base excision repair
Phototherapy and Photobiology Explanation: ***Non-homologous end joining***
- **CRISPR-Cas9** creates a **double-strand break (DSB)** in DNA, which is primarily repaired by **non-homologous end joining (NHEJ)**.
- **NHEJ** is the **predominant repair pathway** in most cells, accounting for 60-90% of DSB repairs.
- **NHEJ** is an error-prone repair mechanism that ligates the broken ends directly, often leading to small **insertions or deletions (indels)** causing gene knockout.
- Note: **Homology-directed repair (HDR)** is another CRISPR-associated mechanism used for precise editing when a donor template is provided, but **NHEJ is the primary endogenous repair pathway**.
*Mismatch repair*
- This mechanism corrects errors that arise during **DNA replication**, such as incorrect base pairing.
- It does not repair **double-strand breaks** induced by CRISPR-Cas9.
*Nucleotide excision repair*
- This pathway removes **bulky DNA adducts** and lesions, such as those caused by UV radiation.
- It is not involved in repairing **CRISPR-Cas9 induced double-strand breaks**.
*Base excision repair*
- This mechanism corrects **damaged or modified bases**, typically single base changes, without affecting the sugar-phosphate backbone significantly.
- It handles different types of DNA damage than the **double-strand breaks** generated by CRISPR-Cas9.
Phototherapy and Photobiology Indian Medical PG Question 3: What is the optimal wavelength of light emitted by a Wood's lamp for dermatological examinations?
- A. 365 nm (Correct Answer)
- B. 400 nm
- C. 320 nm
- D. 200 nm
Phototherapy and Photobiology Explanation: **365 nm**
- A Wood's lamp primarily emits **long-wave UVA light** in the 320 to 400 nm range, with an optimal peak around **365 nm**.
- This specific wavelength is ideal for inducing **fluorescence** in various dermatological conditions, making them visible.
*400 nm*
- While within the UVA range, **400 nm** is at the higher end and may not provide the optimal fluorescence yield for all diagnostic purposes compared to 365 nm.
- Light at 400 nm is closer to the visible light spectrum and might offer less distinction for subtle fluorescence.
*320 nm*
- **320 nm** is at the lower end of the UVA spectrum, bordering on UVB.
- While still capable of inducing some fluorescence, it is generally less effective than 365 nm for the conditions typically examined with a Wood's lamp.
*200 nm*
- **200 nm** falls into the **UVC range** (100-280 nm), which is harmful and not used for diagnostic purposes in a Wood's lamp.
- This wavelength is absorbed by the atmosphere and epidermis and can cause significant **DNA damage**, making it unsafe for routine dermatological examination.
Phototherapy and Photobiology Indian Medical PG Question 4: PUVA therapy is used in all except:
- A. Psoriasis
- B. Vitiligo
- C. Mycosis fungoides
- D. Melasma (Correct Answer)
Phototherapy and Photobiology 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.
Phototherapy and Photobiology Indian Medical PG Question 5: PUVA therapy is used in:
- A. Melasma
- B. Lichen planus
- C. Psoriasis (Correct Answer)
- D. Freckles
Phototherapy and Photobiology Explanation: ***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.
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