Dermatopathology Practice Questions

Q: Which of the following is a melanocytic marker?

HMB-45. **Explanation:** **HMB-45 (Human Melanoma Black-45)** is a highly specific monoclonal antibody used in immunohistochemistry (IHC) to identify melanocytic lesions [1]. It reacts against **gp100**, a glycoprotein found in the stage II premelanosomes of melanocytes. It is particularly useful in diagnosing malignant melanoma, as it typically stains fetal melanocytes and melanoma cells, but is usually negative in normal adult resting melanocytes and intradermal nevi (except for "blue nevi"). **Analysis of Incorrect Options:** * **CD99 (MIC2):** This is a cell surface glycoprotein and a classic marker for **Ewing’s Sarcoma** and Primitive Neuroectodermal Tumors (PNET). It is also seen in lymphoblastic lymphoma and synovial sarcoma. * **NMP-22 (Nuclear Matrix Protein 22):** This is a tumor marker used primarily in the screening and monitoring of **Bladder Cancer** (Urothelial carcinoma) via urine samples. * **CA-125 (Cancer Antigen 125):** This is a well-known tumor marker for **Ovarian Cancer** (specifically epithelial types like serous cystadenocarcinoma). **High-Yield Clinical Pearls for NEET-PG:** * **Other Melanocytic Markers:** Apart from HMB-45, other high-yield markers include **S-100** (most sensitive but least specific), **Melan-A (MART-1)**, **Tyrosinase**, and **SOX10** (highly sensitive for spindle cell and desmoplastic melanomas). * **HMB-45 Utility:** It is excellent for distinguishing melanoma from other "small round blue cell tumors" or undifferentiated carcinomas [1]. * **Negative Marker:** Remember that **Desmoplastic Melanoma** is often negative for HMB-45 but positive for S-100 and SOX10. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Skin, pp. 1146-1152.

Q: What is the characteristic shape of Birbeck granules?

Tennis racket. **Explanation:** **Birbeck granules** are the pathognomonic ultrastructural hallmark of **Langerhans cells** [1]. Under an electron microscope, these organelles appear as rod-shaped structures with a central striated line and a terminal bulbous expansion, giving them a classic **tennis racket** appearance [1]. They are formed by the invagination of the cell membrane and are involved in the endocytosis and trafficking of the protein **Langerin (CD207)** [1]. **Analysis of Options:** * **Tennis racket (Correct):** This is the definitive description used in pathology to describe the morphology of Birbeck granules [1]. * **Hockey stick:** While Birbeck granules are elongated, they do not typically feature the specific angled "blade" associated with a hockey stick. (Note: "Hockey stick" appearance is sometimes used to describe the distribution of the rash in *Incontinentia Pigmenti* or specific ECG findings in Digoxin toxicity). * **Bat:** This shape is not associated with any specific dermatopathological organelle. * **Ball:** Birbeck granules are linear/rod-like, not spherical. **NEET-PG High-Yield Pearls:** 1. **Langerhans Cell Histiocytosis (LCH):** Birbeck granules are the gold-standard diagnostic feature for LCH (formerly Histiocytosis X) [1]. 2. **Immunohistochemistry (IHC):** Langerhans cells are positive for **S-100**, **CD1a**, and most specifically, **Langerin (CD207)** [1]. 3. **Origin:** Langerhans cells are dendritic antigen-presenting cells derived from the bone marrow, primarily located in the *stratum spinosum* of the epidermis. 4. **Electron Microscopy:** It is essential to remember that Birbeck granules are **only** visible under electron microscopy, not light microscopy [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 630.

Question 1

A 74-year-old woman has noted increasing size and number of darker brown patches on the dorsum of each hand for the past 15 years. They do not change with sun exposure, are nonpruritic, and non-tender. On examination, these 0.5- to 1-cm lightly pigmented lesions are flat. Which of the following is the most likely microscopic finding in these lesions?

Accepted Answer

Basal melanocytic hyperplasia

Answer

Dermal nevus cells

Answer

Loss of melanin in surrounding skin

Answer

Mast cell proliferation

Question 2

Which of the following is NOT true about dysplastic nevus syndrome?

Accepted Answer

It is inherited in an autosomal recessive pattern.

Answer

Approximately half of such patients develop melanoma by age 60.

Answer

It is associated with mutations in BRAF and NRAS.

Answer

It is a disorder characterized by numerous dysplastic nevi.

Question 3

A 66-year-old woman presents with a 6-month history of scaling and abnormal pigmentation of the skin. Her past medical history is significant for the treatment of thyroid cancer 1 year ago. Biopsy of lesional skin shows atrophy of the epidermis and dense fibrosis of the dermis, which displays dilated superficial blood vessels. These pathologic findings are most likely caused by previous exposure to which of the following?

Accepted Answer

Radiation therapy

Answer

Chemotherapy

Answer

Corticosteroids

Answer

Organic iodine

Question 4

Which of the following is a melanocytic marker?

Accepted Answer

HMB-45

Answer

CD99

Answer

NMP-22

Answer

CA-125

Question 5

What is the histologic hallmark of Langerhans cells?

Accepted Answer

Birbeck granules

Answer

Dendritic cell processes

Answer

Giant mitochondria

Answer

Eosinophilic granules

Question 6

Which of the following lesions are seen in von Recklinghausen's disease of the skin?

Accepted Answer

Neurofibroma

Answer

Hemangioma

Answer

Ameloblastoma

Answer

Giant cell fibroma

Question 7

What is the characteristic histological feature of basal cell carcinoma?

Accepted Answer

Nuclear palisading

Answer

Keratin pearls

Answer

Foam cells

Answer

Psammoma bodies

Question 8

Pautriers microabscess is seen in which of the following conditions?

Accepted Answer

Mycosis fungoides

Answer

Psoriasis

Answer

Lichen planus

Answer

Leprosy

Question 9

What is the characteristic shape of Birbeck granules?

Accepted Answer

Tennis racket

Answer

Hockey stick

Answer

Bat

Answer

Ball

Question 10

Which of the following is NOT true regarding the histopathology of psoriasis?

Accepted Answer

Pautrier's microabscess

Answer

Epidermal thickening

Answer

Suprapapillary thinning

Answer

Kogoj's spongiform pustules

Dermatopathology — MCQs

Dermatopathology — MCQs

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