Diffuse sclerosing osteomyelitis

Diffuse sclerosing osteomyelitis (DSO) is a chronic, nonbacterial, sterile inflammatory disease of bone that predominantly affects the mandible.[1][2] It is classified as a form of primary chronic osteomyelitis and is now widely considered part of the chronic nonbacterial osteomyelitis (CNO) / SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) spectrum.[3][4] The etiology remains incompletely understood; an autoinflammatory pathogenesis is favored over an infectious one, as bacteriologic cultures are consistently negative and antibiotic-based treatments have historically been ineffective.[5][6] Masticatory muscle overuse (tendoperiostitis) has been proposed as a contributing mechanical factor.[7] The signature imaging pattern is diffuse cortical and medullary sclerosis with subperiosteal new bone formation, in the absence of sequestra or pathological fractures.[2] Management is primarily nonsurgical, with bisphosphonates reserved for refractory cases.[3][8]

• Diffuse sclerosing osteomyelitis (DSO) is the most widely used term in the oral and maxillofacial literature.[1][2]
• Chronic nonbacterial osteomyelitis (CNO) of the mandible is the preferred term in the rheumatologic and pediatric literature and is considered synonymous when the mandible is the affected site.[3][9]
• Chronic diffuse sclerosing osteomyelitis/tendoperiostitis has been used by the Leiden group to emphasize the proposed role of masticatory muscle overuse.[2][8]
• DSO should be distinguished from focal (condensing) sclerosing osteomyelitis, a localized periapical sclerotic reaction to low-grade odontogenic infection, and from proliferative periostitis (Garré osteomyelitis), which is an infection-driven periosteal reaction typically in children with an identifiable odontogenic source.[10]
• When DSO occurs with systemic bone, joint, or cutaneous manifestations, the umbrella term SAPHO syndrome applies; the pediatric multifocal counterpart is chronic recurrent multifocal osteomyelitis (CRMO).[4][11]

• Incidence: Ultra-rare; precise incidence is unknown.[1]
• Sex: Female predilection. In a large cohort of 446 patients, isolated (simple) DSO showed approximately 70% female predominance; syndrome-type DSO was more evenly distributed (≈45% female).[4]
• Age: Onset spans childhood through adulthood. Isolated DSO has a younger median onset (13 years) compared with syndrome-type DSO (25 years). Other series report mean ages in the mid-20s to 40s, reflecting referral patterns.[4][8][12]
• Site: The mandible is affected in the vast majority of cases, with the body and ramus most commonly involved; the condyle may be included. Involvement is predominantly unilateral (≈82–92%), though bilateral disease occurs more frequently in syndrome-type DSO (≈30%).[1][2][4][12]
• Nearly half of DSO patients exhibit systemic bone, joint, or cutaneous manifestations consistent with the SAPHO/CRMO spectrum.[4]

Symptoms and presentation

• Pain is the cardinal symptom, reported in approximately 95% of patients, often severe (VAS 8–10), and characteristically episodic with symptom-free intervals punctuated by acute flares.[1][12]
• Soft-tissue swelling of the face, sometimes producing visible asymmetry, is present in virtually all cases.[12]
• Trismus occurs in roughly half of patients and may mimic temporomandibular disorder (TMD), leading to misdiagnosis.[12][13]

Tempo and course

The disease follows a relapsing-remitting course. Symptom duration before referral often exceeds three years, reflecting diagnostic difficulty.[8] Elevated erythrocyte sedimentation rate (ESR) may be observed during flares, particularly in pediatric CNO.[9] Bone turnover markers (osteocalcin, β-CTX) are frequently elevated, especially in isolated DSO.[4]

Red flags and complications

• Persistent or worsening pain unresponsive to TMD therapy should prompt imaging to exclude DSO.[13]
• Condylar involvement may lead to progressive deformation and functional impairment.[2]
• Systemic screening (skin, joints, other bones) is warranted to identify SAPHO/CRMO manifestations.[1][4]

Location and distribution

DSO involves the mandibular body and ramus, frequently extending over multiple anatomic subregions. The condylar process is involved in a subset of cases.[1][2] Unilateral involvement predominates (>80%), though bilateral disease is recognized, particularly in syndrome-type DSO.[4][12]

Periphery and shape

The margins of DSO are characteristically poorly defined, with an indistinct boundary between affected and normal bone.[12] There is no encapsulation or well-demarcated cortical border separating the lesion from adjacent medullary bone. The overall shape is diffuse and elongated, conforming to the long axis of the mandible rather than forming a discrete mass.

Internal architecture

• Diffuse medullary and cortical sclerosis is the hallmark finding, producing a generalized increase in radiopacity throughout the affected segment on panoramic radiographs.[1][2]
• Small, poorly defined lytic foci may be interspersed within the sclerotic bone, creating a mixed pattern, but frank osteolysis is not a dominant feature.[9][12]
• The trabecular pattern is effaced and replaced by dense, homogeneous sclerosis in advanced disease.
• Sequestra are characteristically absent, a key distinction from chronic suppurative osteomyelitis (CSO) and osteoradionecrosis (ORN).[2]

Subperiosteal new bone formation

Periosteal reaction with subperiosteal new bone formation is a defining radiographic feature, present in 60–70% of cases.[2][4] The periosteal reaction is typically solid or lamellated, adding layers of new bone to the outer cortex and contributing to mandibular enlargement. This feature is more prevalent in isolated DSO than in syndrome-type DSO.[4]

Cortical involvement and extent

• The cortex is thickened and may show areas of discontinuity or lysis, but complete cortical destruction is uncommon.[2][12]
• The corticomedullary boundary becomes blurred or indistinct.[1][12]
• Pathological fractures do not occur in DSO, distinguishing it from CSO and ORN.[2]

Effects on the mandibular canal and teeth

• The inferior alveolar nerve canal appears blurred or obscured on panoramic radiographs and may show enlargement. Mandibular canal enlargement has been associated with a need for repeated bisphosphonate dosing.[1][14]
• Unlike fibrous dysplasia, DSO does not typically cause significant tooth displacement or mandibular canal displacement; rather, the canal is engulfed by sclerotic bone.[12]
• Root resorption is not a prominent feature.

Condylar changes

Condylar process deformation is observed in DSO and is not seen in CSO or ORN, making it a useful discriminator.[2] The condyle may appear enlarged, sclerotic, and irregularly contoured.

Effects on masticatory muscles

Cross-sectional imaging reveals hypertrophy and edema of the masseter and other masticatory muscles ipsilateral to the affected mandible.[2][15] This finding correlates with the clinical trismus and supports the tendoperiostitis hypothesis.

Recognized variants

• Isolated (simple) DSO: Mandible-only disease, younger onset, higher periosteal reaction prevalence, elevated bone turnover markers.[4]
• Syndrome-type DSO: Mandibular disease with systemic bone/joint/skin manifestations (SAPHO spectrum), older onset, higher bilateral involvement, higher CRP.[4]

MRI findings

MRI using a dedicated mandibular coil demonstrates thickened cortical bone (≈86%), contrast enhancement within the mandibular bone (≈79%) and masticatory muscles (≈43%), pathologically enlarged lymph nodes (≈64%), and cortical destruction in approximately 36% of cases.[15] Perineural edema along the inferior alveolar nerve is present in approximately 57% of patients overall and in 100% of patients during active pain relapse, suggesting it may serve as an imaging biomarker for disease flare.[15] MRI is superior to CT for evaluating soft-tissue and perineural inflammatory changes.

Bone scintigraphy

Skeletal scintigraphy shows increased tracer uptake in the affected mandible and is recommended when SAPHO syndrome is suspected, as it can identify clinically occult multifocal skeletal involvement.[1][4] SPECT/CT improves localization and can monitor treatment response; residual low-grade uptake is common even in clinical remission and reflects ongoing bone remodeling.[16]

DSO produces diffuse mandibular sclerosis with periosteal reaction and no sequestra, a pattern that overlaps with several entities. Clinical correlation—particularly the presence of episodic pain, trismus, and negative cultures—is essential for narrowing the differential.

The highest-risk diagnostic pitfall is misdiagnosis as osteosarcoma, given overlapping features of sclerosis, periosteal reaction, and pain. Biopsy is essential when aggressive periosteal reaction, soft-tissue mass, or PDL widening raises concern for malignancy.[18][19]

DSO is a diagnosis of exclusion, and histopathologic findings are nonspecific, which can challenge pathologists.[1]

Microscopic features

• Reactive bone hyperplasia with dense lamellar and woven bone trabeculae in a fibrous stroma is the predominant pattern.[5]
• Areas of woven bone with hypocellular fibroblastic stroma may closely resemble fibrous dysplasia, creating a well-recognized diagnostic overlap.[1][9]
• Additional features described in pediatric CNO include parallel and interconnected osteoid seams, atypical osteoid deposition, and patchy nodular fibrosis.[9]
• Inflammatory infiltrate is typically sparse and nonspecific; acute suppuration and bacterial colonies are absent.[5]
• Cultures are consistently negative for microorganisms.[5]

Radiologic-pathologic correlation

The diffuse medullary sclerosis seen on imaging corresponds to the dense reactive bone hyperplasia on histology. The absence of sequestra radiographically correlates with the absence of necrotic bone fragments histologically, distinguishing DSO from suppurative osteomyelitis.[2][5]

Molecular differentiation

GNAS mutation analysis reliably distinguishes DSO from fibrous dysplasia: activating GNAS mutations at codon 201 are present in approximately 83% of fibrous dysplasia cases but are absent in DSO.[17] This molecular test is recommended when histopathologic overlap precludes confident diagnosis.

Initial workup

Diagnosis requires integration of clinical findings (episodic pain, swelling, trismus, negative cultures), imaging (diffuse sclerosis, periosteal reaction, absent sequestra), and histopathology (reactive bone hyperplasia without suppuration).[1][2] Biopsy is standard to exclude other bone diseases.[1] Screening for SAPHO/CRMO with skeletal scintigraphy and dermatologic evaluation is recommended.[1][4]

First-line treatment

Conservative, nonsurgical management is recommended as the initial approach for both children and adults:[7][8]

• Occlusal splint therapy
• Physiotherapy for masticatory muscles
• Disease counseling
• NSAIDs for symptomatic control during flares

This approach achieved remission in 75% (12/16) of adults and 55% (6/11) of children in prospective series.[7][8]

Second-line treatment

For patients refractory to conservative therapy (typically after 3–12 months), bisphosphonates are the established second-line treatment:[3][22]

• Oral alendronate (70 mg weekly) has demonstrated symptom improvement within 72 hours in case series.[22]
• Intravenous zoledronate suppressed pain in all 18 patients in one series, with median onset of effect at 1 day. Recurrence occurred in 67%, with a median time to recurrence of 29 months. Adverse reactions (flu-like symptoms) occurred in 72% but were minor; no medication-related osteonecrosis of the jaw (MRONJ) was observed.[14]
• A systematic review confirmed bisphosphonate efficacy with minimal MRONJ risk.[3]

Other therapies

Anti-TNF agents (e.g., etanercept) have been reported to achieve complete remission in refractory cases, though evidence is limited to case reports.[6] Radical surgery is discouraged, as outcomes have historically been poor and the disease is nonsuppurative.[5][6]

Prognosis and surveillance

DSO follows a chronic relapsing course. Condylar lesions appear particularly prone to recurrence after bisphosphonate therapy.[14] Long-term follow-up with clinical assessment and periodic imaging is warranted. Patients requiring multiple bisphosphonate doses, particularly those with mandibular canal enlargement, may represent a more refractory subgroup.[14]

SAPHO syndrome association

Nearly half of DSO patients harbor systemic manifestations consistent with SAPHO syndrome, including sternoclavicular hyperostosis, palmoplantar pustulosis, acne, and peripheral arthritis.[4] Simple DSO and syndrome-type DSO show overlapping features but differ in age of onset, sex distribution, and bone metabolic activity, suggesting they may represent different stages or subtypes of the same disease.[4] Rheumatologic referral is appropriate when systemic features are identified.

Pediatric considerations

In children, mandibular CNO is frequently one focus of CRMO rather than an isolated lesion; over half of pediatric patients have a family history of autoimmune or autoinflammatory disease.[9] Conservative therapy remains first-line, but bisphosphonates appear safe in the growing skeleton with minimal risk of skeletal disturbance.[3][7]