Langerhans cell histiocytosis, multifocal/multisystem

Langerhans cell histiocytosis (LCH) is a clonal, inflammatory myeloid neoplasm driven by activating mutations of the MAPK (RAS-RAF-MEK-ERK) pathway, producing lesional CD1a-positive/CD207-positive histiocytes admixed with eosinophils and inflammatory cells.[1][2][3] The multifocal/multisystem forms occupy the aggressive end of a spectrum that ranges from a single indolent bone lesion to disseminated, life-threatening disease.[1][4] In the jaws, the posterior mandible is the most common site, where LCH characteristically produces osteolytic destruction of the alveolar process with the classic "floating teeth" appearance.[5][6] Because oral or jaw lesions may be the first or only manifestation of what proves to be multifocal or multisystem disease, recognition by the dental team is pivotal: a substantial proportion of apparently localized presentations are upstaged after full staging.[7][8] Management is risk-adapted, from local curettage for isolated bone lesions to systemic therapy for multisystem involvement.[2][4]

Current practice classifies LCH within the Langerhans-related "L group" of the Histiocyte Society's 2016 revised classification of histiocytoses, reflecting its recognition as a neoplastic rather than purely reactive process.[4][10] Disease extent, not eponyms, now drives nomenclature and treatment:

• Single-system LCH (SS-LCH): one organ/system, unifocal or multifocal.
• Multisystem LCH (MS-LCH): two or more organs/systems, further stratified as risk-organ-positive (high-risk) or risk-organ-negative (low-risk).[4][7]

The risk organs are the liver, spleen, and hematopoietic system (bone marrow); their involvement defines high-risk disease.[4][10] The older eponyms—Hand–Schüller–Christian disease (chronic disseminated/multifocal), Letterer–Siwe disease (acute disseminated), and eosinophilic granuloma (localized bone)—and the term "histiocytosis X" are obsolete and should be avoided except to prevent confusion with legacy records.[8][11]

LCH is predominantly a disease of childhood, with an annual incidence of approximately 4.6 cases per million children under 15 years and 1–2 per million adults.[1][4] There is a slight male predominance (male-to-female ratio approximately 1.2:1).[1][12] Incidence peaks in infancy, and younger age—particularly the first year of life—correlates with multisystem and risk-organ disease.[11][13] Among US children, incidence is higher in Hispanic and lower in Black populations.[1][13]

Bone is involved in roughly 60–80% of patients overall, and craniofacial bones are among the most frequently affected skeletal sites.[3][10] Within the jaws, the mandible is affected far more often than the maxilla, with a strong predilection for posterior/molar regions; maxillary involvement is uncommon.[5][15] Jaw LCH spans a wide age range but, consistent with the overall disease, is most often diagnosed in children and young adults.[16]

Jaw and oral LCH typically presents with localized swelling and pain, the most frequent complaints, often accompanied by gingival changes.[5][16][17] Characteristic oral findings include:

• Gingival inflammation, hyperplasia, ulceration, and bleeding, frequently mimicking periodontal disease.[8][18][19]
• Loose, mobile, or displaced teeth from alveolar destruction; "floating teeth" may be noted clinically and radiographically.[5][20]
• Mucosal ulceration of gingiva or hard palate, including soft-tissue-only disease.[5][21]
• In infants, premature eruption of teeth and marked periodontal destruction.[20][21]

Tempo is variable, from indolent and chronic to rapidly progressive.[1][10] Because jaw disease may herald systemic involvement, examination should seek red flags of multisystem/high-risk disease: scaly or papular rash, hepatosplenomegaly, lymphadenopathy, cytopenias, and polyuria/polydipsia from arginine vasopressin (AVP) deficiency (diabetes insipidus), the most common endocrinopathy.[3][5][17] Lesions of the orbit, temporal/mastoid, sphenoid, zygomatic and ethmoid bones, maxilla, and paranasal sinuses (and of the anterior or middle cranial fossa with intracranial extension) are CNS-risk sites associated with later pituitary dysfunction and neurodegeneration; the mandible is not.[7]

Location and distribution

Jaw LCH concentrates in the posterior mandible, especially the molar region and ramus; maxillary lesions are much less frequent.[5][15] In multifocal and multisystem disease, lesions may be multiple and bilateral, and can involve both arches simultaneously, producing scattered or coalescing radiolucencies.[5][6] Lesions arise in two patterns: an intraosseous (central, medullary) type and an alveolar type centered on the tooth-bearing bone; intraosseous lesions are the more common.[16]

Relationship to teeth and the alveolar process

Alveolar involvement characteristically begins at the mid-root level rather than at the crestal margin, a useful discriminator from marginal periodontitis.[6] Progressive destruction of supporting bone around roots produces the "floating teeth" / "teeth floating in air" appearance, with teeth apparently suspended in a radiolucent defect.[5][22][23] Lesions may also center at the apices of vital teeth, simulating periapical inflammatory disease.[15][22]

Periphery and shape

Early lesions are well-defined, noncorticated (punched-out) radiolucencies with sharply demarcated borders.[6][22] With growth they enlarge and coalesce into larger, more irregular zones of destruction, and in aggressive multifocal disease the margins may become ill-defined with a moth-eaten quality.[5] Lesions are most often unilocular but can appear multilocular.[5]

Internal architecture

The internal structure is predominantly radiolucent with loss of the normal trabecular pattern.[5][24] Lesions are typically devoid of internal calcification; a true bony septation is not expected, and apparent loculation reflects residual trabeculae.[5]

Effects on teeth and adjacent structures

Beyond floating teeth, LCH may cause tooth displacement and loosening, and may give the impression of teeth being "pushed out" of their sockets.[5][20] Loss of the lamina dura and alveolar crest is common when the periodontium is involved.[6] Overt root resorption is not a characteristic feature, which helps separate LCH from some odontogenic tumors.[5]

Cortical involvement, periosteal response, and extent

Lesions can be expansile with cortical thinning or perforation, and a periosteal reaction (solid or sunburst/spiculated) and perilesional sclerosis have been described in mandibular disease, contributing to overlap with osteomyelitis.[16][25] An adjacent soft-tissue component frequently accompanies craniofacial bone lesions.[23][25] Lesions have a mean diameter of roughly 2 cm but may be considerably larger when multifocal.[16]

Recognized variants

When disease extends to the calvarium, the "hole-within-a-hole" appearance and button sequestrum are classic skull findings that may coexist in craniofacial multifocal disease.[25] Soft-tissue-only (extraosseous) gingival or palatal LCH occurs without a corresponding osteolytic defect.[5]

Whole-body staging

Any jaw lesion confirmed as LCH mandates staging to detect occult multifocal/multisystem disease. Whole-body FDG-PET/CT (vertex to toes) is preferred for detecting additional skeletal and visceral sites and for response assessment in adults and in suspected multisystem disease; a skeletal survey is also used, particularly in children.[3][26] Marrow, liver, and spleen assessment establishes risk-organ status.[10][26]

Soft-tissue extent and CNS-risk evaluation

Cross-sectional imaging better delineates the soft-tissue mass and osseous extent than plain films, and typically shows T2-hyperintense, avidly enhancing lesions with relatively high ADC values that favor LCH over malignancy.[23][25] Because maxillary, orbital, temporal/mastoid, and other skull-base lesions are CNS-risk sites, contrast-enhanced brain/sella MRI is indicated to evaluate the pituitary–hypothalamic axis and neurodegenerative change, especially with AVP deficiency.[3][14]

Jaw LCH is a classic radiographic mimic; the alveolar "mid-root" origin, floating teeth without root resorption, and multifocality are the most useful discriminators, but overlap with infection and malignancy is substantial, so tissue diagnosis is required.

The highest-risk pitfall is treating LCH as refractory osteomyelitis or periodontitis; persistent, atypical, or therapy-resistant jaw destruction—particularly multifocal lesions in a young patient—should prompt incisional biopsy with immunohistochemistry and MAPK-pathway molecular testing, followed by systemic staging.[3][16][19]

Diagnosis rests on identifying lesional Langerhans-type cells with oval, grooved, reniform, or lobulated nuclei, finely granular chromatin, inconspicuous nucleoli, and abundant eosinophilic cytoplasm, typically set in a mixed infiltrate rich in eosinophils and histiocytes, including multinucleated forms.[3][24] The required immunophenotype is CD1a-positive, Langerin/CD207-positive, S100-positive, and cyclin D1-positive, with CD207 and cyclin D1 particularly helpful in distinguishing neoplastic LCH from reactive Langerhans cell collections.[3] Birbeck granules on electron microscopy are classic but no longer required for diagnosis given reliable immunohistochemistry.[24]

Molecular confirmation of clonal MAPK activation supports the diagnosis and guides therapy. BRAF V600E is present in roughly 50–55% of cases (VE1 immunostaining supports but does not replace molecular testing), with MAP2K1, BRAF indels/exon-12 deletions, ARAF, and N/KRAS mutations and rare kinase fusions (BRAF, ALK, RET, NTRK1) accounting for most remaining cases.[3][12] BRAF V600E has been associated with more frequent risk-organ involvement, reactivation, and neurodegeneration.[12] Radiologic–pathologic correlation is essential, because the bland cytology and inflammatory background can mimic osteomyelitis and reactive processes.[3]

Confirmed jaw LCH requires referral for complete staging (history/examination, laboratory evaluation, whole-body imaging, and marrow assessment when counts are abnormal) to determine single-system versus multisystem and risk-organ status before definitive treatment.[3][26] Multidisciplinary coordination (hematology-oncology, oral/maxillofacial surgery, endocrinology, and dentistry) is standard.[17][24]

Treatment is risk-adapted:

• Isolated jaw/bone lesion: conservative local therapy—limited curettage (not aggressive resection) with or without intralesional corticosteroid, with observation for asymptomatic lesions; bisphosphonates or indomethacin are options. Low-dose radiotherapy is reserved for surgically inaccessible or high-risk sites given growth-impairment concerns in children.[3][7][22][25]
• Multifocal bone or multisystem disease:systemic therapy, standard being 12 months of vinblastine plus prednisone, with 6-mercaptopurine added for high-risk disease; cytarabine, cladribine, and clofarabine are important alternatives/salvage agents. For adults, cladribine or cytarabine is commonly used first-line.[3][7][13][26]
• Targeted therapy:BRAF inhibitors (vemurafenib, dabrafenib) for BRAF V600E disease and MEK inhibitors (trametinib, cobimetinib) for other MAPK-pathway mutations produce high response rates but frequent reactivation after discontinuation.[3][11]

Reactivation/recurrence is common—exceeding 30% overall and around 28–34% in multifocal bone and multisystem cohorts—with most relapses within 2–3 years and the majority occurring as (often bone) single-system events that remain salvageable with repeat chemotherapy.[2][27] Surveillance combines interval clinical examination, laboratory testing, and imaging of involved sites, with brain MRI monitoring for CNS-risk and high-risk patients.[3] Prognosis is favorable for localized and low-risk disease (5-year survival over 90%), whereas risk-organ (liver, spleen, marrow) involvement, older adult age, and poor treatment response predict worse survival; permanent consequences—most often endocrine (AVP deficiency, anterior pituitary deficits) and neurodegeneration—are a major long-term burden, particularly after relapse.[11][17][28]