Random Dermatology MCQ - Langerhans Cell Histiocytosis (LCH)

A 2-year-old child presents with a seborrheic dermatitis-like rash on the scalp and intertriginous areas, along with otitis media and lytic bone lesions. A skin biopsy of the rash reveals a dermal infiltrate of cells with grooved, kidney-shaped nuclei and abundant eosinophilic cytoplasm. Electron microscopy of these cells would most likely reveal which of the following cytoplasmic structures?

A) Birbeck granules
B) Weibel-Palade bodies
C) Melanosomes
D) Tonofilaments
E) Michaelis-Gutmann bodies

Correct Answer: A) Birbeck granules

Explanation

This presentation is classic for Langerhans Cell Histiocytosis (LCH), a proliferative disorder of Langerhans cells.

Key Features of Langerhans Cells:

• Origin: Dendritic antigen-presenting cells derived from the bone marrow.

• Location: Primarily in the epidermis (constitute 2-8% of epidermal cells), but also in other stratified squamous epithelia.

• Function: Professional antigen-presenting cells that capture external antigens in the skin, process them, and migrate to lymph nodes to present the antigen to naive T-cells, initiating adaptive immune responses. They are the "sentinels" of the skin immune system.

• Identifying Feature: The pathognomonic ultrastructural feature is the Birbeck granule.

  • Appearance: Tennis racket-shaped or rod-shaped cytoplasmic organelles with a zippered appearance.

  • Function: Believed to be involved in antigen reception and processing.

Clinical Correlation:

• The case describes a child with a triad of:

  1. Skin rash (seborrheic-like)

  2. Bone lesions (lytic)

  3. Otitis media (due to infiltration)

• This is consistent with multisystem Langerhans Cell Histiocytosis.

• The biopsy description of cells with grooved, kidney-shaped nuclei is the classic light microscopy appearance of Langerhans cells.

• Immunohistochemistry: The cells are positive for CD1a and S-100, which is diagnostic.

Why Not the Other Options?

• (B) Weibel-Palade bodies: Found in endothelial cells and contain von Willebrand factor and P-selectin.

• (C) Melanosomes: Found in melanocytes and are the sites of melanin synthesis and storage.

• (D) Tonofilaments: Bundles of keratin intermediate filaments found in keratinocytes, providing structural integrity.

• (E) Michaelis-Gutmann bodies: Laminated, targetoid bodies found in malacoplakia, a rare inflammatory condition often affecting the genitourinary tract.

Prognosis and Management of LCH:

• Varies from spontaneous resolution to progressive, fatal disease depending on the extent of involvement.

• Treatment may include topical steroids for limited skin disease or systemic chemotherapy for multisystem disease.

Note: The combination of the clinical presentation, the histologic finding of cells with grooved nuclei, and the presence of Birbeck granules on electron microscopy is diagnostic for Langerhans Cell Histiocytosis. Langerhans cells are crucial for cutaneous immunity, and their neoplastic proliferation defines LCH.