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Difficulty: Very hardPediatric Hematology and Oncology

A 14-month-old boy is brought to the pediatric clinic by his parents due to a persistent, scaly rash on his scalp and behind his ears that has been present for three months. He has also had chronic, bilateral, purulent ear discharge that has not improved despite three separate courses of oral amoxicillin. Recently, his parents noticed he is excessively thirsty and frequently soaks through his diapers, requiring multiple changes at night. On physical examination, the child is irritable but easily consolable. There is an erythematous, crusted, papular rash over the scalp, postauricular regions, and axillae. Abdominal palpation reveals mild hepatosplenomegaly. A skeletal survey is performed and demonstrates a 2.5-cm sharply marginated, "punched-out" lytic lesion in the right parietal bone without surrounding sclerosis. Which of the following is the most likely finding upon histologic or immunohistochemical evaluation of a biopsy from the bone lesion?

  1. Clonal proliferation of cells that express CD1a and S-100 proteinsAnswer
  2. B
    Heavy infiltration of neutrophils with Gram-positive cocci in clusters
  3. C
    Thickened basement membrane with prominent eosinophilic inclusions
  4. D
    Hyperkeratosis and parakeratosis with abundant Malassezia furfur colonization
  5. E
    Normal trabecular bone architecture with delayed ossification centers

Answer

Clonal proliferation of cells that express CD1a and S-100 proteins
The clinical triad of sharply marginated lytic bone lesions, a seborrheic-like eczematous rash, and central diabetes insipidus (manifesting as polyuria and polydipsia) is classic for Langerhans Cell Histiocytosis (LCH). LCH involves the abnormal clonal proliferation of Langerhans cells, which are specialized dendritic cells of the mononuclear phagocyte system. On immunohistochemical staining, these pathognomonic cells are characteristically positive for CD1a and S-100 surface markers. Furthermore, on electron microscopy, they exhibit distinctive 'tennis racket' shaped intracellular inclusions known as Birbeck granules.

Step-by-Step Solution

1
Analyze the multi-system clinical presentation.
The 14-month-old presents with a therapy-resistant seborrheic-like rash, chronic ear discharge, and signs of central diabetes insipidus (excessive thirst and polyuria).
Identifying these diverse symptoms as part of a single unifying syndrome is required to avoid premature closure on common, benign pediatric diagnoses.
2
Interpret the radiographic findings in the context of the physical exam.
The presence of a sharply marginated, 'punched-out' lytic skull lesion without sclerosis, combined with hepatosplenomegaly, points toward a destructive infiltrative process.
Lytic bone lesions in a child rule out simple developmental delays and strongly suggest an oncologic or severe granulomatous disease.
3
Synthesize the findings to establish the most likely diagnosis.
The classic triad of lytic bone lesions, skin involvement, and central diabetes insipidus is pathognomonic for Hand-Schüller-Christian disease, a systemic variant of Langerhans Cell Histiocytosis (LCH).
Pattern recognition of this triad is essential for identifying this rare pediatric hematology/oncology disorder.
4
Identify the characteristic histologic and molecular markers for the established diagnosis.
LCH is defined by the clonal proliferation of Langerhans cells, which consistently stain positive for CD1a and S-100 markers.
Definitive diagnosis requires biopsy demonstrating these specific immunohistochemical markers.

Key Concept

Diagnosis and histological hallmarks of Langerhans Cell Histiocytosis (LCH)
Estimated Time:2m 0s
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Topics

Pediatric Hematology and Oncology

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