Basic Dermatology Practice Questions

Q: A 16-year-old boy presented with asymptomatic, multiple, erythematous, annular lesions with a collarette of scales at the periphery of the lesions present on the trunk. What is the most likely diagnosis?

Pityriasis rosea. ### Explanation **Correct Option: C. Pityriasis rosea** The clinical presentation of **annular, erythematous lesions** with a characteristic **collarette of scales** (scales attached at the periphery with the free edge pointing inwards) is the hallmark of **Pityriasis rosea (PR)**. PR typically affects adolescents and young adults. It often begins with a single, larger "Herald Patch," followed by a generalized eruption on the trunk and proximal limbs. The lesions follow the lines of cleavage (Langer’s lines), creating the classic **"Christmas Tree" appearance**. It is thought to be associated with Human Herpesvirus 6 and 7 (HHV-6/7). **Why other options are incorrect:** * **A. Pityriasis versicolor:** Presents as hypo- or hyperpigmented macules with fine, "branny" (furfuraceous) scales. It lacks the annular configuration and the specific inward-pointing collarette of scales. * **B. Pityriasis alba:** Characterized by ill-defined, hypopigmented patches with very fine scaling, usually on the face of children. It is considered a manifestation of atopic dermatitis and does not present with erythematous annular lesions. * **D. Pityriasis rubra pilaris (PRP):** Presents with follicular papules on an erythematous base, "islands of sparing" (normal skin within affected areas), and orange-red palmoplantar keratoderma. It does not feature the peripheral collarette of scales. **High-Yield Clinical Pearls for NEET-PG:** * **Herald Patch:** The initial, largest lesion (2–6 cm) seen in 50-90% of PR cases. * **Collarette of Scales:** Scales are attached peripherally and trail toward the center. * **Hanging Curtain Sign:** When the skin is pinched, the scales fold like a curtain (specific to PR). * **Treatment:** Usually self-limiting (6–8 weeks). Reassurance is key; topical steroids or antihistamines are used for pruritus.

Q: Hyperextensibility with normal elastic recoil is a feature of which of the following conditions?

Ehlers Danlos syndrome. **Explanation:** The correct answer is **Ehlers-Danlos Syndrome (EDS)**. **1. Why Ehlers-Danlos Syndrome is correct:** EDS is a group of inherited connective tissue disorders caused by defects in **collagen synthesis** (primarily types I, III, and V). In EDS, the elastic fibers remain structurally normal, but the "collagen scaffolding" that limits skin stretch is defective. This results in **hyperextensibility** (the skin can be pulled far away from the body) with **normal elastic recoil** (the skin snaps back immediately upon release) because the elastin is functional. **2. Why the other options are incorrect:** * **Cutis Laxa:** This is a disorder of **elastic fibers**. Unlike EDS, the skin is loose, pendulous, and lacks resilience. When stretched, it shows **poor/delayed elastic recoil** (it does not snap back). * **Pseudoxanthoma Elasticum (PXE):** This involves progressive calcification and fragmentation of elastic fibers. Clinical features include "plucked chicken" appearance of the skin and angioid streaks in the retina, rather than simple hyperextensibility. * **Scleroderma:** This is characterized by excessive collagen deposition leading to skin **thickening and tightening** (sclerosis). The skin becomes bound down and loses its ability to be pinched or stretched at all. **Clinical Pearls for NEET-PG:** * **EDS Hallmark:** Hyperextensibility + Normal Recoil + Cigarette paper (atrophic) scars + Joint hypermobility. * **Cutis Laxa Hallmark:** Lax, sagging skin + Loss of recoil + "Hook appearance" of the nose. * **Gorlin’s Sign:** Ability to touch the tip of the nose with the tongue (seen in EDS due to hypermobile joints/ligaments). * **Beighton Score:** Used to clinically assess joint hypermobility in EDS.

Q: Pseudo isomorphic phenomenon is seen in which dermatological condition?

Warts. **Explanation:** The **Pseudo-isomorphic phenomenon** refers to the spread of a skin lesion along the path of trauma (such as scratching or shaving) due to the **mechanical inoculation** of an infectious agent. In the case of **Warts (Verruca)**, the Human Papillomavirus (HPV) is autoinoculated into the epidermis through micro-trauma, leading to a linear arrangement of new lesions. This is distinct from the true Koebner phenomenon as it involves an external pathogen rather than an endogenous inflammatory response. **Analysis of Options:** * **Warts (Correct):** As an infectious condition, it exhibits pseudo-isomorphism. Other examples include Molluscum Contagiosum and Plane Warts. * **Psoriasis, Lichen Planus, and Vitiligo (Incorrect):** These conditions exhibit the **True Koebner Phenomenon (Isomorphic Phenomenon)**. In these cases, new lesions characteristic of the underlying disease develop in previously healthy skin following non-specific trauma (e.g., friction, burns, or surgery). This occurs due to an isomorphic response of the skin’s immune system, not infection. **High-Yield Clinical Pearls for NEET-PG:** * **True Koebner Phenomenon:** Seen in Psoriasis (most common), Lichen Planus, and Vitiligo. * **Reverse Koebner:** Disappearance of a lesion following trauma (e.g., Psoriasis, Vitiligo). * **Wolf’s Isotopic Response:** Occurrence of a new skin disease at the exact site of a previously healed, unrelated skin disease (most commonly post-Herpetic scars). * **Renbök Phenomenon:** The disappearance of one skin condition (e.g., Alopecia areata) when another (e.g., Psoriasis) appears in the same area.

Q: Koebner's phenomenon is not seen in which of the following conditions?

Dermatitis herpetiformis. **Explanation:** **Koebner’s Phenomenon** (also known as the isomorphic response) refers to the development of new skin lesions, characteristic of a pre-existing dermatosis, at the site of trauma or injury to previously healthy skin. **Why Dermatitis Herpetiformis is the correct answer:** Dermatitis Herpetiformis (DH) is an autoimmune blistering disorder associated with gluten-sensitive enteropathy. It is characterized by intensely pruritic vesicles on an erythematous base, typically over extensor surfaces. While DH is triggered by gluten and characterized by the deposition of IgA, it **does not** exhibit the Koebner phenomenon. Trauma does not induce new DH lesions; rather, the distribution is determined by systemic factors and specific anatomical predilections. **Analysis of Incorrect Options:** * **Psoriasis:** This is the classic example of Koebner’s phenomenon. New psoriatic plaques frequently appear at sites of scratches, surgical scars, or sunburns. * **Lichen Planus:** This condition frequently demonstrates Koebnerization, where linear lichenoid papules form along scratch marks (often seen on the wrists or shins). * **Vitiligo:** Trauma to the skin can lead to localized melanocyte destruction, resulting in new patches of depigmentation at the site of injury. **High-Yield Clinical Pearls for NEET-PG:** * **True Koebner Phenomenon:** Seen in Psoriasis, Lichen Planus, and Vitiligo. * **Pseudo-Koebner Phenomenon:** Seen in infectious conditions like **Molluscum Contagiosum** and **Verruca (Warts)**, where trauma causes local inoculation/seeding of the virus. * **Reverse Koebner:** The disappearance of a pre-existing lesion following trauma to the site. * **Wolf’s Isotopic Response:** Appearance of a new skin disease at the exact site of a previously healed, unrelated skin disease (most commonly post-Herpes Zoster).

Q: Regarding bulbar xanthelasma, all of the following are true, EXCEPT:

Dots occurring on the lateral side of the eye. **Explanation:** **Xanthelasma palpebrarum** is the most common clinical variant of xanthoma, characterized by localized lipid deposits in the eyelids. 1. **Why Option A is the Correct Answer (The Exception):** Xanthelasma typically presents as soft, velvety, yellow-orange plaques that classically begin at the **medial (inner) canthus** of the eye, most commonly on the upper eyelid. They tend to spread symmetrically. The statement that they occur on the **lateral side** is clinically incorrect, making it the "except" choice. 2. **Analysis of Other Options:** * **Option B (Middle-aged women):** This is a true clinical demographic. While it can occur at any age, the peak incidence is in the 4th and 5th decades, with a slight female preponderance. * **Option C (Creamy yellow in color):** This is the hallmark appearance. The color is due to the accumulation of "foam cells" (lipid-laden macrophages) in the upper dermis. * **Option D (Associated with diabetes):** This is true. While 50% of patients are normolipemic, xanthelasma is frequently associated with secondary hyperlipidemias seen in **Diabetes Mellitus**, biliary cirrhosis, and hypothyroidism, as well as primary dyslipidemias (Type II and IV). **High-Yield Clinical Pearls for NEET-PG:** * **Histopathology:** Look for **Foam cells** (Touton giant cells are more characteristic of Juvenile Xanthogranuloma but can be seen in other xanthomas). * **Systemic Link:** In young patients, xanthelasma is a strong predictor of underlying hyperlipidemia and increased risk of **atherosclerotic cardiovascular disease**. * **Treatment:** Primarily cosmetic; options include surgical excision, TCA cauterization, or CO2 laser ablation. However, recurrence is common (up to 40%).

Q: +ve pathergy test is seen in which of the following conditions?

Behcet's disease. **Explanation:** The **Pathergy Test** is a clinical diagnostic tool used to identify exaggerated skin reactivity to minor trauma. It is performed by pricking the skin (usually the forearm) with a sterile 20-gauge needle. A positive result is defined by the formation of a **sterile erythematous papule or pustule** (at least 2 mm in size) at the site of injury within 24–48 hours. **1. Why Behcet's Disease is Correct:** Behcet’s disease is a multi-systemic inflammatory perivasculitis. The pathergy phenomenon reflects an **overactive neutrophil response** to local trauma. While the test has high specificity (95%+) for Behcet’s, its sensitivity varies geographically, being most reliable in populations along the "Silk Road" (Middle East and East Asia). It is a key minor criterion in the International Study Group criteria for Behcet’s. **2. Why Other Options are Incorrect:** * **Sarcoidosis:** Characterized by non-caseating granulomas. While it shows "Kveim-Siltzbach" skin test positivity (historical), it does not exhibit pathergy. * **Histoplasmosis & Candidiasis:** These are fungal infections. Skin testing for these (like the Histoplasmin test) relies on **Type IV Delayed-Type Hypersensitivity** to specific antigens, not a non-specific inflammatory response to needle trauma. **Clinical Pearls for NEET-PG:** * **Differential Diagnosis for Pathergy:** Apart from Behcet’s, pathergy can also be seen in **Pyoderma Gangrenosum**, Sweet Syndrome, and occasionally in Inflammatory Bowel Disease (IBD). * **Behcet’s Triad:** Recurrent oral ulcers (most common), genital ulcers (most specific), and uveitis. * **HLA Association:** Strongly associated with **HLA-B51**.

Q: Which of the following diseases is itchy and involves the mucosa and the nails?

Lichen planus. **Lichen Planus (LP)** is a chronic inflammatory condition classically characterized by the **"6 Ps"**: Planar (flat-topped), Purple, Polygonal, Pruritic, Papules, and Plaques. It is the most likely diagnosis because it frequently involves the skin, mucous membranes, and nails. * **Mucosal Involvement:** Seen in about 50% of cases, most commonly as **Wickham striae** (reticulate white lines) on the buccal mucosa. * **Nail Involvement:** Occurs in 10% of patients. The pathognomonic finding is **Pterygium formation** (v-shaped scarring of the proximal nail fold onto the nail bed), along with longitudinal ridging and thinning of the nail plate. * **Pruritus:** LP is characteristically very itchy, often leading to the **Koebner phenomenon** (lesions appearing at sites of trauma). **Analysis of Incorrect Options:** * **Psoriasis:** While it involves the skin and nails (pitting, oil spots, onycholysis), it **spares the mucous membranes**. It is also typically less itchy than LP. * **Solar Urticaria:** This is a physical urticaria triggered by UV radiation. It presents with transient wheals on sun-exposed skin and does not involve the nails or mucosa. * **Eczema:** While intensely itchy, eczema (dermatitis) primarily affects the skin. While chronic hand eczema can cause nail dystrophy, it does not typically involve the oral mucosa. **High-Yield Clinical Pearls for NEET-PG:** * **Histopathology:** Look for "Saw-tooth" rete ridges, Civatte bodies (apoptotic keratinocytes), and a band-like lymphocytic infiltrate at the dermo-epidermal junction. * **Associations:** Lichen planus is strongly associated with **Hepatitis C virus** infection. * **Drug-induced LP:** Commonly caused by Beta-blockers, Thiazides, and Antimalarials.

Q: A 26-year-old female presented with diffuse reticulate erythematous to brown, macular, non-blanching discoloration around her umbilicus. There was no evidence of telangiectasia, atrophy, bullae, or superficial erosions. The lesions were asymptomatic, and she frequently applied hot water bags to her abdomen for recurrent abdominal pain. What is the likely diagnosis?

Erythema ab igne. ### Explanation **Correct Answer: B. Erythema ab igne** **1. Why it is correct:** Erythema ab igne (EAI) is a localized, reticulate (net-like) pigmented dermatosis caused by chronic, repeated exposure to **sub-threshold infrared radiation** (heat that is not enough to cause a thermal burn). * **Mechanism:** Chronic heat exposure leads to superficial vascular damage, dermal elastic fiber changes, and epidermal melanin/hemosiderin deposition. * **Clinical Correlation:** The patient’s history of frequent **hot water bag** application for abdominal pain is the classic "trigger." The description of a non-blanching, reticulate, brown-to-red macular rash in the area of heat application is pathognomonic for EAI. **2. Why the other options are incorrect:** * **A. Livedo reticularis:** While also reticulate, this is a vascular pattern caused by sluggish blood flow. It typically blanches with pressure and is often associated with systemic conditions (like SLE or APS) or cold exposure, rather than localized heat. * **C. Poikiloderma atrophicans vasculare:** This presents with a triad of **atrophy, telangiectasia, and mottled pigmentation**. The question explicitly states there was no evidence of atrophy or telangiectasia. * **D. Cutis marmorata:** This is a physiological, transient, reticulate vascular mottling seen in infants or adults when exposed to **cold**. It disappears upon rewarming. **3. NEET-PG High-Yield Pearls:** * **Common Triggers:** Laptop use on thighs ("Laptop thigh"), heating pads, space heaters, or working near furnaces (bakers/blacksmiths). * **Histology:** Similar to actinic keratosis; shows epidermal dysplasia and increased elastic fibers (solar elastosis). * **Long-term Complication:** If the heat source is not removed, there is a small risk of transformation into **Squamous Cell Carcinoma (SCC)** or Merkel cell carcinoma. * **Key Sign:** Always look for the "history of heat exposure" in the clinical stem.

Q: Urticarial lesions are best described as?

evanescent. **Explanation:** Urticaria, commonly known as wheals or hives, is a vascular reaction of the skin characterized by transient upper dermal edema. **Why "Evanescent" is the correct answer:** The hallmark of a classic urticarial wheal is its **evanescent** nature. By definition, individual lesions of urticaria appear rapidly and **resolve within 24 hours** (usually within 2–12 hours) without leaving any residual scarring, pigmentation, or scaling. This occurs because the localized edema (caused by histamine-mediated capillary vasodilation and leakage) is reabsorbed by the lymphatic system. **Analysis of Incorrect Options:** * **A. Nonpruritic:** This is incorrect. Urticaria is almost always **intensely pruritic** (itchy) due to the release of histamine and other mediators that stimulate sensory nerve endings. * **B. Linear:** While "linear urticaria" can occur in **Dermatographism** (physical urticaria triggered by stroking the skin), it is not the standard description for general urticarial lesions, which are typically round, oval, or polycyclic. * **C. Macular:** This is incorrect. A macule is a flat, non-palpable lesion. Urticaria consists of **wheals**, which are elevated, palpable, edematous papules or plaques. **High-Yield Clinical Pearls for NEET-PG:** * **Urticarial Vasculitis:** If an individual urticarial lesion persists for **more than 24 hours**, leaves behind purpura or hyperpigmentation, or is painful rather than itchy, suspect Urticarial Vasculitis (confirmed via skin biopsy). * **Angioedema:** This represents the same pathological process as urticaria but involves the **deep dermis and subcutaneous tissue**. * **Darier’s Sign:** Rubbing a lesion of Mastocytosis (Urticaria Pigmentosa) results in a localized wheal; this is a classic exam favorite. * **Treatment:** The first-line treatment for acute and chronic urticaria is **Second-generation H1 antihistamines** (e.g., Cetirizine, Loratadine).

Q: What condition is detected by green fluorescence during a Wood's lamp examination?

Pseudomonas. **Explanation:** The correct answer is **Pseudomonas**. Wood’s lamp examination is a diagnostic tool that uses ultraviolet light (365 nm) to detect specific skin conditions based on their characteristic fluorescence. **Why Pseudomonas is correct:** *Pseudomonas aeruginosa* produces a pigment called **pyoverdin** (also known as fluorescein). When skin infected with Pseudomonas (such as in burn wounds or "hot tub folliculitis") is exposed to a Wood’s lamp, it emits a characteristic **apple-green fluorescence**. This is a high-yield clinical marker for identifying the colonization of this gram-negative bacterium in clinical settings. **Analysis of Incorrect Options:** * **Corynebacterium diphtheriae:** Does not show fluorescence. However, *Corynebacterium minutissimum* (the causative agent of **Erythrasma**) is a classic Wood's lamp favorite, showing a **coral-red fluorescence** due to porphyrin production. * **Pneumococcus:** This bacterium does not possess fluorophores and does not exhibit fluorescence under UV light. * **Microsporum canis:** While this fungal species *does* fluoresce, it typically produces a **bright blue-green** fluorescence. In the context of this specific question, Pseudomonas is the classic association for distinct green fluorescence. **High-Yield Clinical Pearls for NEET-PG:** 1. **Tinea Capitis:** *Microsporum* species (e.g., *M. canis, M. audouinii*) show **Blue-Green** fluorescence. *Trichophyton schoenleinii* shows **Dull Green**. 2. **Pityriasis Versicolor:** Caused by *Malassezia furfur*, it shows **Yellowish-white or Copper-orange** fluorescence. 3. **Erythrasma:** Shows **Coral-red** fluorescence. 4. **Porphyria Cutanea Tarda:** Urine shows **Pink-orange** fluorescence. 5. **Vitiligo:** Shows **milky-white** fluorescence (due to total loss of melanin), helping to distinguish it from pityriasis alba.

Question 1

A 16-year-old boy presented with asymptomatic, multiple, erythematous, annular lesions with a collarette of scales at the periphery of the lesions present on the trunk. What is the most likely diagnosis?

Accepted Answer

Pityriasis rosea

Answer

Pityriasis versicolor

Answer

Pityriasis alba

Answer

Pityriasis rubra pilaris

Question 2

Hyperextensibility with normal elastic recoil is a feature of which of the following conditions?

Accepted Answer

Ehlers Danlos syndrome

Answer

Pseudoxanthoma elasticum

Answer

Cutis laxa

Answer

Scleroderma

Question 3

Pseudo isomorphic phenomenon is seen in which dermatological condition?

Accepted Answer

Warts

Answer

Vitiligo

Answer

Lichen planus

Answer

Psoriasis

Question 4

Koebner's phenomenon is not seen in which of the following conditions?

Accepted Answer

Dermatitis herpetiformis

Answer

Vitiligo

Answer

Psoriasis

Answer

Lichen planus

Question 5

Regarding bulbar xanthelasma, all of the following are true, EXCEPT:

Accepted Answer

Dots occurring on the lateral side of the eye

Answer

Occurs in middle-aged women

Answer

Creamy yellow in color

Answer

Associated with diabetes

Question 6

+ve pathergy test is seen in which of the following conditions?

Accepted Answer

Behcet's disease

Answer

Sarcoidosis

Answer

Histoplasmosis

Answer

Candidiasis

Question 7

Which of the following diseases is itchy and involves the mucosa and the nails?

Accepted Answer

Lichen planus

Answer

Psoriasis

Answer

Solar urticaria

Answer

Eczema

Question 8

A 26-year-old female presented with diffuse reticulate erythematous to brown, macular, non-blanching discoloration around her umbilicus. There was no evidence of telangiectasia, atrophy, bullae, or superficial erosions. The lesions were asymptomatic, and she frequently applied hot water bags to her abdomen for recurrent abdominal pain. What is the likely diagnosis?

Accepted Answer

Erythema ab igne

Answer

Livedo reticularis

Answer

Poikiloderma atrophicans vasculare

Answer

Cutis marmorata

Question 9

Urticarial lesions are best described as?

Accepted Answer

evanescent

Answer

nonpruritic

Answer

Linear

Answer

macular

Question 10

What condition is detected by green fluorescence during a Wood's lamp examination?

Accepted Answer

Pseudomonas

Answer

Corynebacterium diphtheria

Answer

Pneumococcus

Answer

Microsporum canis

Basic Dermatology — MCQs

Basic Dermatology — MCQs

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