Diffuse Idiopathic Skeletal Hyperostosis

Diffuse idiopathic skeletal hyperostosis (DISH) is a non-inflammatory skeletal disorder characterised by flowing calcification and ossification along the anterolateral aspects of at least four contiguous vertebral bodies, predominantly affecting the thoracic spine. It is associated with ossification of peripheral entheses (ligament and tendon insertions) throughout the axial and peripheral skeleton. DISH is common, underdiagnosed, and frequently confused with ankylosing spondylitis (AS) or degenerative disc disease.

In Australia, DISH affects approximately 10–20% of adults over 60 years of age and is more prevalent in men, people with type 2 diabetes, obesity, and metabolic syndrome. Prevalence increases dramatically with age, reaching 25–35% in those over 70. It is increasingly recognised as a systemic manifestation of metabolic dysregulation rather than a purely mechanical condition.

The pathogenesis of DISH involves dysregulated entheseal bone formation driven by metabolic factors. Unlike inflammatory arthropathies, DISH is not primarily driven by immune activation or synovial inflammation.

Key Pathogenic Mechanisms

• Insulin and insulin-like growth factor (IGF-1): Hyperinsulinaemia (as in metabolic syndrome and type 2 diabetes) stimulates osteoblast proliferation and new bone formation at entheses — the strongest metabolic driver of DISH
• Retinoid signalling: Vitamin A derivatives and retinoids promote periosteal bone formation; chronic high retinol intake is a risk factor for DISH
• Mechanical stress: Repetitive entheseal loading contributes to localised ossification at tendon/ligament insertions
• Adipokines (leptin, adiponectin): Adipose tissue-derived factors modulate bone remodelling; obesity-associated adipokine dysregulation promotes ectopic ossification
• Genetic susceptibility: Associations with COL6A3 polymorphisms and genes regulating bone morphogenetic protein (BMP) signalling

Anatomical Distribution

DISH preferentially involves the right side of the thoracic spine — possibly due to pulsation inhibition from the descending aorta on the left side. The thoracic spine (T7–T11 most commonly) is the primary site. Other common sites include the cervical spine, lumbar spine, calcaneal entheses, olecranon, iliac crest, and patella.

Metabolic Associations

DISH is frequently asymptomatic and discovered incidentally on imaging. When symptomatic, the most common complaints are spinal stiffness and reduced range of motion, particularly thoracic. Pain is typically mild to moderate — much less severe than inflammatory spondyloarthropathy.

Spinal Manifestations

• Thoracic stiffness: Reduced thoracic rotation and lateral flexion; dull aching mid-back pain worsening with prolonged static posture
• Lumbar stiffness: Reduced lumbar flexion/extension; may be mistaken for degenerative disc disease
• Cervical DISH: Upper cervical ossification may cause dysphagia (anterior osteophytes compressing oesophagus), dysphonia, sleep apnoea, or cervical myelopathy
• Cervical myelopathy (rare): Upper motor neuron signs, gait disturbance, hand clumsiness — due to posterior longitudinal ligament ossification (OPLL) or anterior osteophyte cord compression
• Fracture: DISH segments are relatively brittle — low-energy trauma can cause fractures through fused spinal segments (hyperextension injuries); these are unstable and highly dangerous

Peripheral Enthesopathy

• Calcaneal enthesopathy: Posterior heel pain (Achilles insertion) and plantar heel pain (plantar fascia insertion) — common and often bilateral
• Olecranon enthesopathy: Triceps insertion pain at elbow
• Patellar enthesopathy: Quadriceps or patellar tendon insertion pain
• Iliac crest / greater trochanter: Hip abductor insertion pain
• Shoulder: Rotator cuff enthesopathy, subacromial entheseal ossification

Features Distinguishing DISH from Ankylosing Spondylitis

Diagnosis of DISH is radiological. The Resnick criteria (1976) remain the standard for diagnosis and require flowing ossification along the anterolateral aspects of at least four contiguous thoracic vertebrae, with preservation of disc height and absence of facet joint ankylosis or sacroiliac joint erosion.

• Inv-Essential
  Thoracic and Lumbar Spine X-Ray

  First-line imaging. Shows characteristic 'flowing candle wax' ossification along the anterior vertebral column, typically right-sided in the thoracic spine. Disc heights are preserved. Absence of sacroiliitis confirms DISH over AS. Resnick criteria: ≥4 contiguous vertebral bodies, preserved disc height, no sacroiliac erosion.
• Inv-Essential
  Cervical Spine X-Ray

  Indicated if cervical symptoms (dysphagia, dysphonia, neck stiffness, myelopathy). Anterior osteophytes most prominent at C4–C7. CT preferred for detailed assessment of degree of anterior osteophyte formation and oesophageal compression.
• Inv-Recommended
  CT Spine

  Better delineation of ossification extent, facet joint status, and spinal canal dimensions. Essential if: (1) myelopathy suspected, (2) fracture evaluation after trauma, (3) pre-operative planning. CT whole-spine for fracture evaluation in trauma — plain X-ray misses up to 50% of DISH fractures.
• Inv-Recommended
  MRI Spine

  Indicated for: myelopathy symptoms (cord compression assessment), fracture with soft tissue/cord involvement, or to distinguish DISH from inflammatory spondylitis. MRI shows cord signal change in myelopathy.
• Inv-Essential
  Fasting Glucose and HbA1c

  Screen for type 2 diabetes in all patients with DISH. Metabolic syndrome is strongly associated. HbA1c preferred for diagnosis and monitoring. Tight glycaemic control may slow DISH progression.
• Inv-Essential
  Fasting Lipid Profile

  Screen for dyslipidaemia (component of metabolic syndrome). Uric acid if gout suspected (co-occurrence common). BMI and waist circumference as part of metabolic assessment.
• Inv-Recommended
  CRP and ESR

  Should be NORMAL in DISH — elevated inflammatory markers suggest alternative or co-existing diagnosis (inflammatory spondyloarthropathy, infection, malignancy). HLA-B27 testing if AS considered in differential.
• Inv-Recommended
  Barium Swallow or Fibreoptic Endoscopy

  Indicated if dysphagia present. Assesses degree of oesophageal compression from anterior cervical osteophytes. Referral to gastroenterology or ENT for management.

DISH severity is stratified by the presence and severity of complications. Most patients have asymptomatic or mildly symptomatic disease; a minority develop clinically significant complications requiring specialist intervention.

Fracture Risk in DISH

Dysphagia Severity (Cervical DISH)

• Mild: Intermittent difficulty with solids; compensates with dietary modification
• Moderate: Difficulty with solids and semi-solids; weight loss risk; aspiration risk
• Severe: Unable to swallow solids or liquids; aspiration pneumonia risk; surgical intervention often required

DISH has no disease-modifying therapy proven to halt or reverse ossification. Pharmacological management focuses on symptom control (pain and stiffness) and addressing modifiable metabolic risk factors. Unlike ankylosing spondylitis, biological DMARDs (TNF inhibitors, IL-17 inhibitors) are NOT indicated for DISH.

Analgesia and Anti-inflammatory Agents

Management of Metabolic Comorbidities

• Type 2 diabetes: Optimise glycaemic control (HbA1c target <53 mmol/mol for most); metformin first-line; SGLT2 inhibitors and GLP-1 agonists have additional bone-protective effects
• Obesity: Weight loss reduces entheseal mechanical loading and improves metabolic profile; refer to dietitian and bariatric program if BMI >35
• Gout: Urate-lowering therapy (allopurinol, febuxostat) if uric acid elevated and gout confirmed
• Dyslipidaemia: Statin therapy per cardiovascular risk guidelines; rosuvastatin preferred in patients with diabetes
• Retinoid use: Avoid high-dose retinol supplements; consider switching systemic retinoids (acitretin, isotretinoin) to alternative therapies if DISH is progressing

Specific complications of DISH require targeted interventions beyond general symptom management. Early recognition and specialist referral is critical for severe dysphagia and myelopathy.

Dysphagia Management (Cervical DISH)

Myelopathy Management

• Urgent neurosurgery referral for any DISH-related myelopathy
• MRI spine to define level and extent of cord compression
• Surgical decompression (laminectomy or anterior decompression) is the definitive treatment
• Avoid high-dose corticosteroids for DISH myelopathy — no evidence of benefit
• Post-operative physiotherapy for neurological rehabilitation

Fracture Management

• Spinal precautions immediately in any DISH patient with trauma and new spinal pain
• CT whole-spine to exclude fracture — plain X-ray is insufficient
• All DISH spinal fractures should be managed as potentially unstable — urgent spine surgery referral
• DISH fractures have high rates of neurological deterioration and mortality — early surgical stabilisation is usually required
• Rigid cervical collar provides some initial immobilisation pending definitive management

Peripheral Enthesopathy Management

• Calcaneal enthesopathy: Stretching, silicone heel cups, NSAIDs, physiotherapy; corticosteroid injection if refractory (short-term benefit only)
• Plantar fasciitis: Stretching exercises, orthotics, ESWT (extracorporeal shock wave therapy — covered by some health funds in Australia)
• Other enthesopathies: Physiotherapy, load management, NSAIDs; ultrasound-guided corticosteroid injection for refractory cases

Physiotherapy is central to DISH management. The primary goals are maintaining spinal and joint mobility, preventing further stiffness, and optimising function. Exercise does not worsen or accelerate ossification.

Spinal Mobility Program

• Thoracic extension exercises: Foam roller thoracic extension, doorway chest openers, thoracic rotation — counteract kyphotic stiffening from ossification
• Cervical mobility: Gentle range-of-motion exercises (flexion, extension, rotation, lateral flexion) — particularly important in cervical DISH to prevent myelopathy from hypomobility
• Lumbar mobility: Cat-cow, knee-to-chest stretches, lumbar rotation
• Hydrotherapy: Warm water exercise — ideal for generalised stiffness; reduces joint loading while enabling mobilisation
• Frequency: Daily home exercise program; 2–3 supervised physiotherapy sessions initially to establish safe technique

Occupational Therapy

• Assessment of activities of daily living impacted by reduced spinal mobility
• Assistive devices: long-handled shoe horns, reachers, elevated toilet seats for patients with severe spinal rigidity
• Driving assessment if cervical rotation severely limited (safety concern)
• Workplace ergonomic review if spinal stiffness affects work capacity

Weight Management and Lifestyle

• Weight loss is both metabolically therapeutic (reduces hyperinsulinaemia) and mechanically beneficial (reduces entheseal loading)
• Referral to dietitian for structured weight management program
• Mediterranean diet pattern: reduces insulin resistance and systemic inflammation
• Avoid high-dose vitamin A (retinol) supplements — risk factor for DISH progression
• Adequate calcium and vitamin D intake for bone health (particularly important in elderly patients)

Fall Prevention

Monitoring for DISH focuses on: (1) metabolic comorbidity control, (2) surveillance for complications (dysphagia, myelopathy, fracture risk), and (3) functional status and mobility.

Metabolic Monitoring Targets

Neurological Surveillance

• Assess for myelopathy signs at each visit: Hoffman's sign, hyperreflexia, clonus, Babinski — particularly if cervical DISH
• Assess for new dysphagia with direct question at each visit — cervical osteophytes grow silently
• MRI cervical/thoracic spine if new neurological symptoms — do not delay

🩺 Type 2 Diabetes

Type 2 diabetes is the strongest modifiable risk factor for DISH. Patients with diabetes and DISH require aggressive metabolic management.

• HbA1c optimisation is the primary goal — hyperinsulinaemia drives DISH progression
• SGLT2 inhibitors (empagliflozin, dapagliflozin): reduce insulin resistance, body weight, and cardiovascular risk — preferred in patients with DISH and established CVD or heart failure
• GLP-1 receptor agonists (semaglutide, dulaglutide): significant weight loss, reduce insulin resistance — suitable for obese patients with DISH and T2DM
• Metformin: first-line; weight-neutral to weight-reducing; reduces hepatic glucose output

👴 Elderly Patients

• Elderly patients with DISH have high fracture risk — falls prevention program is essential
• NSAIDs require careful consideration: renal function, GI risk, cardiovascular risk — prefer COX-2 inhibitor or paracetamol
• Physiotherapy and hydrotherapy preferred over pharmacological management
• Dysphagia in elderly DISH patients increases aspiration pneumonia risk — swallowing assessment important
• Concurrent osteoporosis common — DXA and bone-protective therapy (bisphosphonate) if indicated

🔬 Patients on Systemic Retinoids

• Systemic retinoids (acitretin for psoriasis; isotretinoin for acne) are independent risk factors for DISH-like ossification
• Spinal imaging before and during long-term systemic retinoid therapy in at-risk patients
• Consider switching to alternative agents if DISH is progressing on retinoid therapy
• Avoid high-dose vitamin A supplements (>3,000 µg/day retinol) in all DISH patients

💼 Patients with Occupational Spinal Demands

• Manual workers with DISH have reduced spinal mobility — ergonomic workplace assessment and modified duties may be required
• Cervical DISH with restricted rotation may limit safe driving and operating machinery — driving assessment referral
• Heavy lifting with rigid fused spine increases fracture risk — occupational physiotherapy and task modification

🛡️ Post-Traumatic Management

• Any DISH patient presenting after trauma (including minor falls) with new spinal pain requires immediate spinal precautions and CT whole-spine
• Normal neurological examination does NOT exclude unstable fracture — radiological clearance mandatory
• Coordinate with emergency medicine and spine surgery for acute trauma assessment

Stewardship for DISH focuses on avoiding inappropriate prescribing of biological therapies (which are ineffective and costly), overuse of imaging, and inappropriate surgical referral for asymptomatic disease.

NSAID Stewardship

• NSAIDs in DISH are for symptomatic relief only — they do NOT slow ossification or disease progression
• Use minimum effective dose for minimum duration; reassess regularly
• Avoid long-term NSAIDs in elderly patients — GI, renal, and cardiovascular risk outweighs modest symptomatic benefit
• Topical NSAIDs (diclofenac gel) appropriate for peripheral enthesopathy — lower systemic risk

Surgical Stewardship

• Surgery (osteophytectomy, decompression) is indicated only for complications: severe dysphagia, myelopathy, or unstable fracture
• Asymptomatic DISH with incidental imaging findings does NOT require surgical referral
• Post-osteophytectomy recurrence of anterior cervical ossification occurs in 30–50% of cases within 5 years — patient counselling required

Long-term follow-up for DISH focuses on metabolic comorbidity management, complication surveillance, and maintaining functional mobility through exercise.

Prevention of Complications

• Metabolic optimisation: Best evidence for slowing progression — glycaemic control, weight loss, retinoid avoidance
• Exercise: Daily spinal mobility exercises prevent progressive stiffness and reduce fall risk
• Fall prevention: Balance training, home hazard modification, footwear assessment — reduces catastrophic fracture risk
• Patient education: Awareness of fracture risk, when to seek emergency care, recognising dysphagia and myelopathy symptoms
• Medication review: Avoid agents that accelerate DISH (high-dose retinoids); optimise metabolic medications

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