Question 1

Which sign is pathognomonic for neurofibromatosis?

Accepted Answer

Axillary freckling. **Explanation:**

**Neurofibromatosis Type 1 (NF1)**, also known as von Recklinghausen disease, is an autosomal dominant multisystem disorder. The correct answer is **Axillary freckling (Crowe sign)** because it is considered highly specific (pathognomonic) for NF1.

1.  **Axillary Freckling (Crowe Sign):** These are small, 1–3 mm hyperpigmented macules found in intertriginous areas (axilla or groin). Unlike solar lentigines, they appear in areas not exposed to the sun. Their presence is a hallmark diagnostic criterion for NF1.
2.  **Cafe-au-lait macules (CALMs):** While these are often the first sign of NF1, they are **not pathognomonic**. CALMs can be seen in healthy individuals, McCune-Albright syndrome, Fanconi anemia, and Legius syndrome. In NF1, the presence of 6 or more macules (>5mm in prepubertal; >15mm in postpubertal) is required for diagnosis.
3.  **Shagreen patch:** This is a connective tissue nevus (leathery plaque) typically found on the lower back. It is a characteristic feature of **Tuberous Sclerosis**, not Neurofibromatosis.

**High-Yield Clinical Pearls for NEET-PG:**
*   **Lisch Nodules:** Iris hamartomas (seen on slit-lamp exam) are the most common ocular finding in NF1.
*   **Optic Glioma:** The most common CNS tumor associated with NF1.
*   **Sphenoid Wing Dysplasia:** A classic skeletal deformity in NF1.
*   **Genetics:** NF1 is caused by a mutation in the *NF1* gene on **Chromosome 17** (encodes Neurofibromin), while NF2 is linked to **Chromosome 22** (encodes Merlin). [Practice more Dermatology questions on OnCourse]

Question 2

What is the primary lesion in lichen planus?

Accepted Answer

Papule. **Explanation:**

The primary lesion in **Lichen Planus (LP)** is classically described by the **"6 Ps"**: **P**lanar (flat-topped), **P**urple (violaceous), **P**olygonal, **P**ruritic, **P**apules, and **P**laques.

1.  **Why Papule is Correct:** A papule is a solid, raised lesion less than 1 cm in diameter. In LP, the characteristic lesion is a violaceous, flat-topped papule. These papules often coalesce to form larger **plaques**. The surface of these papules typically shows fine, white, lace-like patterns known as **Wickham striae**, which are a hallmark diagnostic feature.

2.  **Why Other Options are Incorrect:**
    *   **Macule:** This is a flat, non-palpable change in skin color. While post-inflammatory hyperpigmentation (macules) is common after LP heals, the active primary lesion is always raised.
    *   **Vesicle/Bullae:** These are fluid-filled blisters (vesicles <0.5 cm; bullae >0.5 cm). While a rare variant called "Bullous Lichen Planus" exists, these are not the *primary* or most common presentation of the disease.

**High-Yield Clinical Pearls for NEET-PG:**
*   **Histopathology:** Look for the "saw-tooth" appearance of rete pegs, basal cell degeneration (liquefaction necrosis), and a band-like lymphocytic infiltrate at the dermo-epidermal junction.
*   **Koebner Phenomenon:** LP shows a positive Koebner phenomenon (lesions appearing at sites of trauma).
*   **Associations:** Often associated with **Hepatitis C** infection.
*   **Civatte Bodies:** These are apoptotic keratinocytes found in the lower epidermis/upper dermis, also known as colloid or cytoid bodies. [Practice more Dermatology questions on OnCourse]

Question 3

Which of the following is not a type of leukoplakia?

Accepted Answer

Bullous. **Explanation:**

**Leukoplakia** is clinically defined as a "predominantly white patch or plaque of the oral mucosa that cannot be characterized clinically or pathologically as any other disease." It is a premalignant condition.

**Why Bullous is the correct answer:**
Leukoplakia is classified based on its clinical morphology into **Homogenous** and **Non-homogenous** types. **Bullous** is not a recognized clinical variant of leukoplakia. Bullous lesions (blisters) are characteristic of immunobullous disorders (like Pemphigus) or infections, but they do not form the clinical spectrum of leukoplakia, which is primarily a keratotic or dysplastic process.

**Analysis of Incorrect Options:**
*   **Homogenous (Option D):** This is the most common type. It presents as a uniform, flat, thin, white plaque with a smooth, wrinkled, or corrugated surface. It carries a lower risk of malignancy.
*   **Non-Homogenous types:** These carry a higher risk of malignant transformation and include:
    *   **Speckled (Option C):** Also known as Erythroleukoplakia. It consists of white flecks or nodules on an erythematous (red) base.
    *   **Ulcerative (Option A):** Characterized by an ulcerated area within the white patch; this is often a red flag for invasive squamous cell carcinoma.
    *   **Verrucous:** A subtype with a thick, wart-like, irregular surface.

**Clinical Pearls for NEET-PG:**
*   **Most common site:** Buccal mucosa.
*   **Highest risk of malignancy:** Speckled (Erythroleukoplakia) and Proliferative Verrucous Leukoplakia (PVL).
*   **Biopsy:** Mandatory to rule out dysplasia or Squamous Cell Carcinoma (SCC).
*   **Hairy Leukoplakia:** Unlike oral leukoplakia, this is caused by **EBV** in HIV patients and is *not* premalignant. [Practice more Dermatology questions on OnCourse]

Question 4

Facial edema, cheilitis granulomatosa, and a fissured tongue characterize which of the following syndromes?

Accepted Answer

Melkerson-Rosenthal syndrome. **Explanation:**

**Melkersson-Rosenthal Syndrome (MRS)** is a rare neurocutaneous disorder characterized by a classic diagnostic triad. The correct answer is B because the question describes this specific triad:
1.  **Recurrent facial edema:** Usually non-pitting and painless, most commonly involving the lips.
2.  **Cheilitis granulomatosa:** Chronic swelling of the lip due to granulomatous inflammation (Miescher’s cheilitis is considered a monosymptomatic form of MRS).
3.  **Fissured tongue (Lingua plicata):** Present in approximately 30–50% of cases.

**Analysis of Incorrect Options:**
*   **A. Frey's Syndrome (Auriculotemporal Syndrome):** Characterized by localized sweating and flushing in the parotid area while eating (gustatory sweating), usually following parotid surgery or trauma. It does not involve tongue fissuring or granulomatous cheilitis.
*   **C. Treacher Collins Syndrome:** A genetic disorder of craniofacial development (mandibulofacial dysostosis) presenting with downward-slanting eyes, micrognathia, and malformed ears. It is a structural developmental defect, not an inflammatory/edematous condition.

**NEET-PG High-Yield Pearls:**
*   **The Triad:** Only about 20–25% of patients present with the complete triad simultaneously.
*   **Facial Nerve Palsy:** Recurrent, lower motor neuron type facial palsy is the third component of the triad (often replacing or accompanying the edema).
*   **Histopathology:** Skin biopsy of the lip shows **non-caseating granulomas**, similar to sarcoidosis or Crohn’s disease.
*   **Mnemonic:** Remember **"M-R-S"** — **M**outh (Cheilitis), **R**elapsing paralysis (Facial palsy), **S**plit tongue (Fissured). [Practice more Dermatology questions on OnCourse]

Question 5

Xanthoma disseminatum is associated with which of the following conditions?

Accepted Answer

Diabetes Insipidus. **Explanation:**

**Xanthoma disseminatum (XD)** is a rare, benign, non-Langerhans cell histiocytosis (non-LCH). It is characterized by the triad of **cutaneous xanthomas**, **mucosal involvement**, and **diabetes insipidus**.

1.  **Why Diabetes Insipidus is correct:**
    The underlying pathophysiology involves the proliferation of histiocytes in various tissues. In approximately **40% of cases**, these histiocytic infiltrates involve the pituitary stalk or the hypothalamus. This leads to a deficiency in Vasopressin (ADH), resulting in **central Diabetes Insipidus**. The cutaneous lesions typically appear as small, reddish-brown to yellow papules and nodules symmetrically distributed over the face and flexural areas (axilla, groin).

2.  **Why the other options are incorrect:**
    *   **A. Down’s Syndrome:** While associated with certain dermatological conditions like syringomas and alopecia areata, it has no known association with XD.
    *   **C. Lymphoma:** XD is a benign histiocytic proliferation. While some other xanthomatous conditions (like Necrobiotic Xanthogranuloma) are associated with paraproteinemias or malignancies, XD is not typically linked to lymphoma.
    *   **D. Carcinoma of Pancreas:** There is no established clinical link between XD and pancreatic malignancy.

**High-Yield Clinical Pearls for NEET-PG:**
*   **Normolipemic State:** Unlike most other xanthomas, Xanthoma Disseminatum occurs in patients with **normal lipid profiles**.
*   **The Triad:** Cutaneous lesions + Mucosal lesions (upper airway/oral) + Diabetes Insipidus.
*   **Montgomery’s Syndrome:** Another name for Xanthoma Disseminatum.
*   **Histology:** Features "Touton giant cells" and foamy macrophages (histiocytes) that are **S100 negative** and **CD68 positive** (confirming non-LCH origin). [Practice more Dermatology questions on OnCourse]

Dermatology Questions

Topics

Basic Dermatology

Dermatological Pharmacology

Bacterial Skin Infections

Viral Skin Infections

Fungal Skin Infections

Parasitic Skin Infections

Acne and Related Disorders

Pigmentary Disorders

Dermatitis and Eczema

Psoriasis

Blistering Diseases

Autoimmune Skin Diseases

Skin Tumors

Dermatological Procedures

Hair and Nail Disorders

Cosmetic Dermatology

Tropical Dermatology

Pediatric Dermatology

Occupational Dermatoses

Phototherapy and Photobiology

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