Dermatology MCQ - Infiltrative and Neoplastic Disorders - Papular xanthoma

A normolipemic 3-year-old child presents with multiple, firm, yellow to reddish-yellow papules and nodules scattered on the trunk and extremities. The lesions have appeared over the past few months and are asymptomatic. A biopsy of one lesion reveals a dense, well-circumscribed dermal infiltrate of foamy histiocytes. Notably, Touton giant cells and other inflammatory cells are absent. What is the most likely diagnosis?

A. Juvenile xanthogranuloma
B. Papular xanthoma
C. Xanthoma disseminatum
D. Benign cephalic histiocytosis
E. Erdheim-Chester disease

Correct Answer: B. Papular xanthoma

Answer and Explanation

The correct answer is B. This question describes the classic presentation of papular xanthoma. The key clues are the age (childhood), the morphology (asymptomatic yellow papules/nodules), the normolipemic state (normal blood lipids), and the specific histology: a dense infiltrate of foamy histiocytes with a conspicuous absence of Touton giant cells and significant inflammation. This "pure" foamy cell infiltrate is the hallmark that distinguishes it from its closest mimic, juvenile xanthogranuloma.

Why the Other Options are Incorrect:

• A. Juvenile xanthogranuloma (JXG): This is the most common histiocytosis in this age group and a key differential. However, JXG typically has a more polymorphous infiltrate that characteristically includes Touton giant cells, lymphocytes, and eosinophils. The absence of Touton giant cells in the biopsy is the critical feature pointing away from JXG and toward papular xanthoma.

• C. Xanthoma disseminatum: This condition presents in older children and adults. It is characterized by a dramatic eruption of hundreds to thousands of red-brown to yellow papules and nodules that have a strong predilection for flexures and mucous membranes (eyes, mouth, upper respiratory tract) and can be associated with diabetes insipidus. The clinical distribution and systemic associations are not described here.

• D. Benign cephalic histiocytosis (BCH): BCH presents as red-brown macules and papules, not yellow papules/nodules. Furthermore, BCH is almost exclusively confined to the head and neck region, not the trunk and extremities. The histiocytes in BCH are not typically foamy.

• E. Erdheim-Chester disease (ECD): This is a serious, multisystem non-Langerhans cell histiocytosis of adults. It is characterized by symmetric sclerosis of long bones and infiltrates in organs like the heart, lungs, and retroperitoneum. It is not a purely cutaneous disorder of childhood.

Additional High-Yield Information for Exams:

• Histopathology: The diagnosis hinges on the histology. It shows a well-circumscribed, dense dermal nodule composed almost entirely of monomorphous, lipid-laden foamy histiocytes with small, central nuclei. The absence of Touton giant cells is a defining feature. The immunophenotype is consistent with a non-Langerhans cell histiocytosis: the cells are CD68+, CD163+, Factor XIIIa+, and are CD1a- and S-100-.

• Clinical Features:

  • Age: Most common in infants and children, but can occur in adults.

  • Lipid Status: Patients are almost always normolipemic, which distinguishes it from the xanthomas associated with hyperlipidemia (e.g., eruptive xanthomas).

  • Course: The lesions are benign and often undergo spontaneous regression over months to years.

• Differential Diagnosis: The main differential is with other non-Langerhans cell histiocytoses. The most important distinction is from Juvenile Xanthogranuloma (JXG). Papular xanthoma is characterized by a pure infiltrate of mature foamy histiocytes with minimal to no inflammation and a definitive lack of Touton giant cells. In contrast, Juvenile Xanthogranuloma shows a polymorphous infiltrate with a mixture of histiocytic cells, including non-foamy early forms, and the pathognomonic presence of Touton giant cells, often accompanied by other inflammatory cells like lymphocytes and eosinophils.

• Prognosis: Excellent. It is a benign, self-resolving condition.

• Management & Rationale:

  • Rationale: The primary goal is to confirm the diagnosis via biopsy to rule out other histiocytoses and to provide reassurance about the self-limited nature of the condition.

  • First-line: Clinical diagnosis, confirmation with biopsy, and reassurance. No active treatment is necessary.

  • Monitoring: Simple observation is all that is required. The family should be educated about the expected natural history of spontaneous resolution.