Dermatology MCQ - Infiltrative and Neoplastic Disorders - Benign cephalic histiocytosis

A healthy 2-year-old child develops multiple, small, red-brown macules and papules confined to the face and ears. The lesions are asymptomatic and have been gradually increasing in number over the past year. The child is otherwise well, with no systemic symptoms, organomegaly, or diabetes insipidus. A biopsy of one lesion reveals a dermal infiltrate of histiocytes with abundant, pale cytoplasm. The histiocytes are positive for CD68 and negative for CD1a and S-100. What is the most likely diagnosis and expected outcome?

A. Benign cephalic histiocytosis; lesions typically undergo spontaneous regression within a few years.
B. Generalized eruptive histiocytoma; lesions are more widespread and often persist into adulthood.
C. Juvenile xanthogranuloma; lesions are typically larger, yellow-colored, and contain Touton giant cells.
D. Langerhans cell histiocytosis; requires systemic workup due to potential for multi-organ involvement.
E. Urticaria pigmentosa; lesions would demonstrate Darier's sign and a dermal mast cell infiltrate.

Correct Answer: A. Benign cephalic histiocytosis; lesions typically undergo spontaneous regression within a few years.

Answer and Explanation

The correct answer is A. This question describes the classic presentation of benign cephalic histiocytosis (BCH). The key clues are the age (infants/young children), the exclusive location on the head and neck ("cephalic"), the morphology (small, red-brown maculopapules), and the benign clinical course. The immunophenotype (CD68+, CD1a-, S-100-) confirms it is a non-Langerhans cell histiocytosis. The most important point is that BCH is self-limited and resolves spontaneously without sequelae.

Why the Other Options are Incorrect:

• B. Generalized eruptive histiocytoma: This condition presents with recurrent crops of widespread histiocytomas on the trunk and extremities, not confined to the head and neck. The lesions are more numerous and can persist longer.

• C. Juvenile xanthogranuloma (JXG): While JXG can occur on the head, the lesions are typically larger, dome-shaped nodules that are yellow or orange-brown in color due to lipid accumulation. The histology of JXG is more polymorphous and characteristically shows Touton giant cells, which are not a feature of BCH.

• D. Langerhans cell histiocytosis (LCH): This is the most critical entity to rule out. However, LCH cells are CD1a+ and S-100+. Furthermore, LCH often has scale, crust, or purpura and is associated with a significant risk of systemic involvement, which is not described here.

• E. Urticaria pigmentosa: This form of cutaneous mastocytosis presents as red-brown macules or papules that urticate (form a wheal) when rubbed (Darier's sign). Histology would show a dermal infiltrate of mast cells, not histiocytes.

Additional High-Yield Information for Exams:

• Histopathology: BCH shows a relatively sparse, superficial dermal infiltrate of monomorphous histiocytes with abundant, pale, eosinophilic cytoplasm. The nuclei are oval or reniform (kidney-shaped). The key is the absence of Touton giant cells and the negative staining for CD1a and S-100.

• Immunophenotype: The histiocytes in BCH are positive for markers of the monocyte/macrophage lineage, such as CD68, CD163, and Factor XIIIa. This profile places it within the spectrum of non-Langerhans cell histiocytoses.

• Differential Diagnosis: The main differential, as outlined, is with other histiocytoses of childhood, particularly the early macular stage of JXG and LCH. The location (head/neck) and immunophenotype are key to distinguishing it.

• Associated Conditions & Prognosis:

  • Prognosis: Excellent. BCH is a benign, self-resolving condition. The lesions typically involute spontaneously over a period of 2 to 5 years, often leaving no trace or slight hyperpigmentation.

  • Association: There are rare case reports of BCH evolving into other non-Langerhans cell histiocytoses, such as generalized eruptive histiocytoma, but this is not the typical course.

• Management & Rationale:

  • Rationale: The primary goal is to correctly diagnose the condition to provide reassurance and avoid unnecessary investigations or treatments for more sinister conditions like LCH.

  • 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.