Dermatology MCQ - Infiltrative and Neoplastic Disorders - Steatocystoma multiplex

A 20-year-old man presents with numerous, soft, yellow to skin-colored, compressible cystic nodules on his chest and axillae that have been developing since adolescence. The lesions range from a few millimeters to over 1 cm in diameter. A biopsy of one lesion is performed. Which of the following histopathological findings is pathognomonic for this condition?

A. A cyst wall composed of stratified squamous epithelium with a granular layer, surrounding laminated keratin.
B. A cyst wall composed of epithelial cells without a granular layer, surrounding compact eosinophilic keratin.
C. A thin cyst wall lined by an eosinophilic, corrugated cuticle, with sebaceous glands embedded within or directly adjacent to the wall.
D. A cystic structure filled with vellus hairs and laminated keratin.
E. A cystic structure lined by ciliated, columnar epithelium.

Correct Answer: C. A thin cyst wall lined by an eosinophilic, corrugated cuticle, with sebaceous glands embedded within or directly adjacent to the wall.

Answer and Explanation

The correct answer is C. This question describes the classic presentation of steatocystoma multiplex. The key clinical clues are the onset in adolescence/adult life, the distribution on the chest and axillae (sebaceous-rich areas), and the description of soft, compressible, yellow nodules. The pathognomonic histologic feature is the corrugated, eosinophilic cuticle lining the cyst wall, along with the presence of sebaceous gland lobules within the cyst wall itself. The cyst contains an oily liquid composed of sebum and keratin.

Why the Other Options are Incorrect:

• A. A cyst wall... with a granular layer, surrounding laminated keratin: This is the classic histology of an epidermoid cyst.

• B. A cyst wall... without a granular layer, surrounding compact eosinophilic keratin: This is the classic histology of a pilar (trichilemmal) cyst.

• D. A cystic structure filled with vellus hairs and laminated keratin: This describes an eruptive vellus hair cyst.

• E. A cystic structure lined by ciliated, columnar epithelium: This describes a branchial cleft cyst, which is a developmental cyst found in the neck, not on the trunk.

Additional High-Yield Information for Exams:

• Histopathology: The diagnosis hinges on the unique cyst wall.

  • Wall: Very thin, consisting of only a few layers of epithelial cells.

  • Lining: The inner surface is lined by a characteristic eosinophilic, corrugated (wavy) cuticle.

  • Sebaceous Glands: Mature sebaceous lobules are typically present within the fibrous cyst wall. This is a key diagnostic feature.

  • Contents: The cyst is filled with a clear or oily yellow fluid, not solid keratin.

• Pathogenesis: The cysts are thought to originate from the pilosebaceous duct, specifically the sebaceous duct.

• Differential Diagnosis: The main clinical differential includes:

  • Eruptive Vellus Hair Cysts (EVHC): Lesions are often more hyperpigmented and follicular, and contain vellus hairs, not oil.

  • Multiple Epidermoid or Pilar Cysts: These are typically firmer and contain solid keratin, not a liquid content.

  • Lipomas: These are solid tumors of fat, not cysts, and are not typically yellow and compressible in the same way.

• Associated Conditions & Prognosis:

  • Inheritance: Often sporadic, but familial cases with autosomal dominant inheritance occur, associated with mutations in the KRT17 gene.

  • Association: The KRT17 mutation is also associated with pachyonychia congenita type 2.

  • Prognosis: The condition is benign but can be a significant cosmetic concern for patients. The cysts can become inflamed, infected, or form fistulae.

• Management & Rationale:

  • Rationale: Management is challenging as there is no perfect cure. The goal is to improve appearance and manage symptomatic lesions.

  • First-line: Reassurance about the benign nature.

  • Medical Therapy: Oral isotretinoin can reduce the size and oiliness of the cysts by shrinking sebaceous glands, but the cysts typically recur after discontinuation.

  • Surgical/Procedural Options:

    • Simple Incision and Expression: Can be effective for individual cysts but recurrence is common if the cyst wall is not removed.

    • Complete Surgical Excision: The only definitive treatment for a single cyst, but impractical for widespread disease due to scarring.

    • Carbon Dioxide Laser: Can be used to vaporize the cyst roof and drain the contents, with good cosmetic results.