Basic Dermatology Practice Questions

Q: Sawtooth rete ridges are seen in:

Lichen planus. ***Lichen planus*** - **Sawtooth rete ridges** are a characteristic histological feature of **lichen planus**, observed as pointed epidermal rete ridges between which a band-like inflammatory infiltrate is present. - This pattern is due to the destruction of the **basal layer** and subsequent architectural changes in the dermal-epidermal junction. *Psoriasis* - Psoriasis is characterized by **elongated and clubbed rete pegs**, not sawtooth rete ridges. - Other key histological features include **parakeratosis**, **neutrophilic microabscesses**, and **dilated blood vessels** in the dermal papillae. *Erythroderma* - Erythroderma is a clinical presentation of widespread erythema and scaling and not a specific disease with unique histological features. - Histology in erythroderma is **non-specific**, showing features of the underlying causative dermatosis (e.g., psoriasis, eczema) but typically no sawtooth rete ridges on its own. *Darier's disease* - Darier's disease is characterized by **dyskeratosis**, **acantholysis**, and suprabasal clefts. - It presents with distinctive **corps ronds** and **grains** in the epidermis, which are not related to sawtooth rete ridges.

Q: Wood's Lamp is used in the diagnosis of:

Pityriasis versicolor. ***Pityriasis versicolor*** - A Wood's lamp is used to diagnose **Pityriasis versicolor** as the affected areas fluoresce a characteristic **golden yellow** (sometimes yellow-green) color due to the presence of porphyrins produced by the Malassezia fungus. - This diagnostic tool helps in visualizing subtle lesions and confirming the diagnosis of this superficial fungal infection. *Tinea pedis* - **Tinea pedis**, or athlete's foot, is typically diagnosed clinically based on symptoms like **itching, scaling, and redness**, or through **potassium hydroxide (KOH) microscopy** of skin scrapings to visualize hyphae. - A Wood's lamp is generally **not useful** for Tinea pedis, as the causative dermatophytes usually do not fluoresce. *Sporotrichosis* - **Sporotrichosis** is a subcutaneous fungal infection usually diagnosed by **fungal culture** from lesional tissue or aspiration, and sometimes by **histopathology**. - A Wood's lamp is **not used** in the diagnosis of sporotrichosis as the Sporothrix schenckii fungus does not exhibit fluorescence under UV light. *All of the options* - This option is incorrect because a Wood's lamp is only reliably used for **Pityriasis versicolor** among the given choices, due to the characteristic fluorescence of the causative organism. - It does not aid in the diagnosis of **Tinea pedis** or **Sporotrichosis**.

Q: Koebner's phenomenon seen in ?

All of the options. ***All of the options*** - **Koebner's phenomenon** (isomorphic response) refers to the development of new lesions at sites of **skin trauma** in patients with pre-existing dermatological conditions. - **All four conditions listed** can exhibit Koebner's phenomenon, making this the correct answer. **Psoriasis** - The **most classic and frequently cited** example of Koebner's phenomenon. - Physical injury triggers characteristic red, scaly plaques at trauma sites. - Seen in approximately **25-50%** of psoriasis patients. **Vitiligo** - Well-documented to exhibit **Koebner's phenomenon**. - New **depigmented patches** appear at sites of trauma, cuts, or friction. - Important diagnostic and prognostic indicator in vitiligo patients. **Lichen planus** - Classic condition showing **Koebner's phenomenon**. - New violaceous, flat-topped papules develop at trauma sites. - One of the hallmark features of this condition. **Lichen nitidus** - Although less commonly emphasized, **Lichen nitidus can exhibit Koebner's phenomenon**. - Tiny, shiny papules may appear in linear distribution following trauma. - Part of the lichenoid reaction group that shows isomorphic response.

Q: All the following can cause mouth ulcers except ?

Psoriasis. ***Psoriasis*** - While psoriasis is an inflammatory condition affecting the skin, nails, and joints, it typically does **not cause mouth ulcers** [3], [4]. Oral lesions in psoriasis are rare and atypical, presenting as geographic tongue-like lesions or plaques rather than ulcerations. - The primary lesions of psoriasis are **erythematous plaques with silvery scales**, not aphthous-like ulcers found in the oral cavity [3]. *Sickle cell anemia* - Individuals with sickle cell anemia can experience **oral manifestations** due to chronic hypoxia and impaired microcirculation, including delayed healing and increased susceptibility to infections. - **Recurrent aphthous ulcers** are reported to be more common in patients with sickle cell disease, possibly due to their compromised immune status and tissue perfusion [1]. *Mouth washes* - Certain ingredients in **mouthwashes**, especially those containing strong detergents like **sodium lauryl sulfate (SLS)** or high concentrations of alcohol, can cause irritation and breakdown of the oral mucosa. - This irritation can lead to the development of **chemical burns** or **ulcerations**, particularly with prolonged or frequent use in sensitive individuals. *Lichen planus* - **Oral lichen planus** commonly presents with various lesions in the mouth, including reticular (Wickham's striae), atrophic, erythematous, bullous, and ulcerative forms [2]. - **Erosive and ulcerative forms** of lichen planus are especially painful and can mimic recurrent aphthous ulcers, making it a direct cause of mouth ulcers [1], [2].

Q: Koebner's phenomenon is seen in all EXCEPT:

Pemphigoid. ***Pemphigoid*** - **Pemphigoid** is an autoimmune blistering skin condition not typically associated with the Koebner phenomenon. - In pemphigoid, **bullae** arise from an autoimmune attack on **hemidesmosomes**, not from isomorphic response to trauma. *Psoriasis* - **Psoriasis** is a classic example of a condition exhibiting the Koebner phenomenon, where isomorphic lesions develop at sites of trauma. - This response is due to **keratinocyte proliferation** triggered by injury in genetically predisposed individuals. *Warts* - **Warts** (verrucae) can demonstrate the Koebner phenomenon, meaning that new warts can emerge along a line of trauma or scratching. - This is attributed to the local spread of the **human papillomavirus (HPV)** through minor excoriations. *Lichen planus* - **Lichen planus** frequently exhibits the Koebner phenomenon, where characteristic **purplish, polygonal papules** emerge at sites of skin injury. - This isomorphic response is a common diagnostic clue in active disease.

Q: Coral red color on Wood's lamp is seen in –

Erythrasma. ***Erythrasma*** - **Erythrasma** is a superficial bacterial infection caused by *Corynebacterium minutissimum*, which produces **porphyrins**. - These **porphyrins** fluoresce a characteristic **coral red** under a **Wood's lamp** (UV light of 365 nm). *Vitiligo* - **Vitiligo** causes depigmentation of the skin. Under a Wood's lamp, affected areas appear as a **bright, stark white** or bluish-white due to the complete absence of melanin. - There is no **coral red fluorescence** associated with vitiligo. *Pseudomonas* - Infections caused by **Pseudomonas** (e.g., *Pseudomonas aeruginosa*) can produce pigments that fluoresce under a Wood's lamp, typically appearing **green** or **blue-green**. - This is distinct from the **coral red** seen in Erythrasma. *Tinea* - **Tinea** (dermatophyte) infections may or may not fluoresce under a Wood's lamp; when they do, species like *Microsporum canis* or *Microsporum audouinii* typically produce a **blue-green** or **apple-green** fluorescence. - Most superficial dermatophyte infections, such as those caused by *Trichophyton* species, **do not fluoresce** at all.

Q: Mucosa is involved in:

Lichen planus. ***Lichen planus*** - **Lichen planus** frequently involves the mucous membranes, especially the **oral mucosa**, presenting as **Wickham's striae** (lacy white patterns). - Genital, esophageal, laryngeal, and conjunctival mucosa can also be affected, leading to erosions or papules. - This is the **classic dermatological condition** with significant mucosal involvement. *Scabies* - **Scabies** is a parasitic skin infestation caused by the **mite** *Sarcoptes scabiei*, primarily affecting the skin, especially intertriginous areas. - It does not involve mucous membranes, as the mites burrow into the epidermis only. *Psoriasis* - **Psoriasis** is predominantly a **skin disorder** characterized by red, scaly plaques. - Mucosal involvement is **extremely rare** (unlike lichen planus where it is common). - While geographic tongue and rare oral lesions have been described, typical mucosal involvement is not a feature of psoriasis. *Alopecia* - **Alopecia** refers to **hair loss** and is a condition primarily affecting hair follicles in the scalp or other hairy areas of the body. - It does not involve the mucous membranes, which are non-hairy epithelial linings.

Q: Wood lamp is used to diagnose –

Tinea versicolor. ***Tinea versicolor*** - A Wood lamp is used to diagnose **tinea versicolor** by revealing a characteristic **yellow-green fluorescence** of the affected areas due to the production of **porphyrins** by the causative yeast, *Malassezia*. - This specific fluorescence helps differentiate **tinea versicolor** from other skin conditions that may have a similar appearance. *Erysipelas* - **Erysipelas** is a superficial bacterial skin infection, typically diagnosed based on its **clinical presentation** of a rapidly spreading, fiery red, tender, and sharply demarcated rash. - A Wood lamp is **not used** in the diagnosis of erysipelas, as it does not cause any specific fluorescence under UV light. *Pityriasis rosea* - **Pityriasis rosea** is a self-limiting inflammatory skin rash, usually diagnosed clinically by its distinctive morphology, including a **herald patch** followed by smaller, oval, fawn-colored lesions in a "Christmas tree" pattern. - A Wood lamp examination would **not show any specific fluorescence** indicative of pityriasis rosea. *Psoriasis* - **Psoriasis** is a chronic autoimmune skin condition characterized by well-demarcated, erythematous plaques covered with silvery scales, typically diagnosed through **clinical examination** and sometimes a skin biopsy. - A Wood lamp is **not a diagnostic tool** for psoriasis, as psoriatic lesions do not fluoresce in a characteristic manner under UV light.

Q: Erythema nodosum is seen in all Except

Salicylate poisoning. ***Salicylate poisoning*** - **Salicylate poisoning** is a toxic condition resulting from an overdose of aspirin or related compounds and is not associated with erythema nodosum. - Symptoms primarily involve **gastrointestinal disturbance**, **tinnitus**, **metabolic acidosis**, and **respiratory alkalosis**. *Tuberculosis* - **Erythema nodosum** can be a manifestation of primary **tuberculosis**, representing a hypersensitivity reaction to mycobacterial antigens. - It often occurs in children or young adults with recent **Mycobacterium tuberculosis** infection. *Leprosy* - **Erythema nodosum leprosum** is a specific type of erythema nodosum seen in **leprosy**, particularly during type 2 lepra reactions. - It presents as multiple, tender, erythematous nodules often accompanied by **fever** and **systemic symptoms**. *Typhoid* - **Typhoid fever** (enteric fever) can rarely be associated with **erythema nodosum** as a cutaneous manifestation of the systemic infection caused by **Salmonella Typhi**. - Other skin findings in typhoid include **rose spots**, which are more characteristic.

Q: A young boy presented to OPD with multiple shiny pinhead size white papules over dorsum of head, forearm and penis. What would be the diagnosis?

Lichen nitidus. ***Lichen nitidus*** - Characterized by **multiple, shiny, pinpoint, flesh-colored to whitish papules**, often seen on the upper extremities, trunk, genitalia, and flexural areas. - The lesions are typically **asymptomatic** but can sometimes be pruritic. *Scabies* - Presents with intensely **pruritic** papules, vesicles, and burrows, especially in interdigital spaces, wrists, and waistline. - The lesions are usually *erythematous* and excoriated due to scratching, which does not match the description of shiny white papules. *Lichen planus* - Typically presents as **pruritic, purple, polygonal, planar papules and plaques** (the "6 Ps"). - Often associated with **Wickham's striae** (fine white lines) and can affect mucous membranes, nails, and hair, which is distinct from the described lesions. *Molluscum contagiosum* - Characterized by **dome-shaped, flesh-colored, pearly papules** with a central **umbilication** caused by a poxvirus. - The lesions are usually larger than "pinhead size" and have a characteristic central dimple not described here.

Question 1

Sawtooth rete ridges are seen in:

Accepted Answer

Lichen planus

Answer

Psoriasis

Answer

Erythroderma

Answer

Darier's disease

Question 2

Wood's Lamp is used in the diagnosis of:

Accepted Answer

Pityriasis versicolor

Answer

Tinea pedis

Answer

Sporotrichosis

Answer

All of the options

Question 3

Koebner's phenomenon seen in ?

Accepted Answer

All of the options

Answer

Lichen nitidus

Answer

Psoriasis

Answer

Vitiligo

Question 4

All the following can cause mouth ulcers except ?

Accepted Answer

Psoriasis

Answer

Sickle cell anemia

Answer

Mouth washes

Answer

Lichen planus

Question 5

Koebner's phenomenon is seen in all EXCEPT:

Accepted Answer

Pemphigoid

Answer

Psoriasis

Answer

Warts

Answer

Lichen planus

Question 6

Coral red color on Wood's lamp is seen in –

Accepted Answer

Erythrasma

Answer

Vitiligo

Answer

Pseudomonas

Answer

Tinea

Question 7

Mucosa is involved in:

Accepted Answer

Lichen planus

Answer

Scabies

Answer

Psoriasis

Answer

Alopecia

Question 8

Wood lamp is used to diagnose –

Accepted Answer

Tinea versicolor

Answer

Erysipelas

Answer

Pityriasis rosea

Answer

Psoriasis

Question 9

Erythema nodosum is seen in all Except

Accepted Answer

Salicylate poisoning

Answer

Tuberculosis

Answer

Leprosy

Answer

Typhoid

Question 10

A young boy presented to OPD with multiple shiny pinhead size white papules over dorsum of head, forearm and penis. What would be the diagnosis?

Accepted Answer

Lichen nitidus

Answer

Scabies

Answer

Lichen planus

Answer

Molluscum contagiosum

Basic Dermatology — MCQs

Basic Dermatology — MCQs

On this page

Practice by Chapter

Want unlimited practice?