A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 2-year-old boy is brought to the physician with complaints of gingival growth in the lower jaw with associated pain for the past few weeks. He has no history of trauma or any other significant medical conditions. His temperature is 37.0°C (98.6°F), pulse is 92/min, and respiratory rate is 24/min. On extraoral examination, a swelling of 4 cm x 2 cm is present on the left lower jaw. On intraoral examination, a diffuse erythematous swelling covered with necrotic slough is present on the gingiva. Computed tomography (CT) scan of the head shows multiple soft tissue density lesions involving mandibular, maxillary, left occipital, and temporal regions. Which of the following findings, if present, would be the most specific indicator of the disease in this patient?
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A
Ragged red fibersIncorrect. Ragged red fibers are characteristic of mitochondrial myopathies (e.g., MELAS, MERRF) on muscle biopsy — irrelevant to LCH.
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B
Prominent perifascicular and paraseptal atrophyIncorrect. Perifascicular atrophy with perimysial inflammation is characteristic of DERMATOMYOSITIS, a muscle disease — not related to multifocal jaw/skull lytic lesions.
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C
Birbeck granulesCorrect. Birbeck granules (rod-shaped or tennis-racquet cytoplasmic inclusions on EM) are the highly specific morphologic finding for Langerhans cell histiocytosis, the most likely diagnosis here.
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D
Endomysial inflammatory infiltrates and myofiber necrosisIncorrect. Endomysial inflammation with myofiber necrosis is the hallmark of POLYMYOSITIS, an inflammatory myopathy — not a feature of LCH.
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E
Reed-Sternberg cells on lymph node biopsyIncorrect. Reed-Sternberg cells are pathognomonic for Hodgkin lymphoma, which presents with painless cervical/supraclavicular lymphadenopathy and B symptoms — not multifocal lytic bone lesions of the jaw and skull characteristic of Langerhans cell histiocytosis.
↑ Tap an answer to reveal the reasoning
Answer: C. A young child with painful gingival/mandibular swelling and necrotic mucosa, plus CT showing MULTIPLE lytic-appearing soft-tissue lesions in the mandible, maxilla, occipital, and temporal regions, is the classic multifocal presentation of LANGERHANS CELL HISTIOCYTOSIS (LCH) — formerly known as Histiocytosis X. LCH is a clonal proliferation of pathologic Langerhans cells (CD1a+, S100+, Langerin/CD207+) that can present as a solitary bone lesion (eosinophilic granuloma) or as disseminated disease (Hand-Schüller-Christian, Letterer-Siwe).
The most SPECIFIC histologic feature on electron microscopy is the presence of BIRBECK GRANULES — rod- or tennis-racquet-shaped cytoplasmic inclusions unique to Langerhans cells and pathologic LCH cells. Immunohistochemistry with CD1a and Langerin/CD207 is the modern diagnostic standard, but Birbeck granules remain the classic 'morphologic specific' answer on board exams.
Clinical syndromes within LCH spectrum: (1) Eosinophilic granuloma = single lytic bone lesion. (2) Hand-Schüller-Christian = chronic multifocal with the triad of lytic skull lesions + diabetes insipidus (posterior pituitary infiltration) + exophthalmos. (3) Letterer-Siwe = acute disseminated infantile form with hepatosplenomegaly, lymphadenopathy, skin rash, and pancytopenia — very aggressive.
This patient (multiple lytic skull/jaw lesions in a 2-year-old) fits Hand-Schüller-Christian / multifocal LCH. Treatment depends on extent: solitary bone lesions may resolve spontaneously or with curettage; multisystem disease is treated with chemotherapy (vinblastine + prednisone).
The distractors target muscle pathologies: ragged red fibers (mitochondrial myopathy), perifascicular atrophy (dermatomyositis), endomysial infiltrate with myofiber necrosis (polymyositis) — none relate to LCH.
**Why each option:**
**A.** Ragged red fibers are characteristic of mitochondrial myopathies (e.g., MELAS, MERRF) on muscle biopsy — irrelevant to LCH.
**B.** Perifascicular atrophy with perimysial inflammation is characteristic of DERMATOMYOSITIS, a muscle disease — not related to multifocal jaw/skull lytic lesions.
**C.** Correct — Birbeck granules (rod-shaped or tennis-racquet cytoplasmic inclusions on EM) are the highly specific morphologic finding for Langerhans cell histiocytosis, the most likely diagnosis here.
**D.** Endomysial inflammation with myofiber necrosis is the hallmark of POLYMYOSITIS, an inflammatory myopathy — not a feature of LCH.