DISH (Diffuse Idiopathic Skeletal Hyperostosis) - Spine

Introduction

A very common disorder of unknown etiology that is characterized by back pain and spinal stiffness
- defined by presence of non-marginal syndesmophytes at three successive levels (involving 4 contiguous vertebrae)
- also known as Forestier disease
- can include enthesopathy of the spine, shoulder, elbow, knee and calcaneus
Epidemiology
- demographics
  - overall incidence 6-12%
  - uncommon before 50 years old
  - prevelence
    - > 50 y.o. (25% males; 15% females)
    - > 80 y.o. (28% males; 26% females)
  - less common in Black, Native-American and Asian populations
- location
  - occurs anywhere in spine
    - most common in the thoracic spine (right side) > cervical > lumbar
      - postulated to be due to the protective effect of the pulsatile aorta on the left of the thoracic spine
    - symmetrical in the cervical and lumbar spine (syndesmophytes both on left and right of the spine)
- risk factors
  - gout
  - hyperlipidemia
  - diabetes
Diagnostic criteria
- flowing ossification along the anterolateral aspect of at least 4 contiguous vertebrae
- preservation of disk height in the involved vertebral segment; relative absence of significant degenerative changes (e.g. marginal sclerosis in vertebral bodies or vacuum phenomenon)
- absence of facet-joint ankylosis; absence of SI joint erosion, sclerosis or intraarticular osseous fusion
Associated conditions
- lumbar spine
  - lumbar spinal stenosis
- cervical spine
  - dysphagia and stridor
  - hoarseness
  - sleep apnoea
  - difficulty with intubation
  - cervical myelopathy
- spine fracture and instability
  - because ankylosis of vertebral segments proximal and distal to the fracture creates long lever arms that cause displacement even in low-energy injuries
  - hyperextension injuries are common
  - seemingly minor, low energy injury mechanisms may result in unstable fracture patterns. One must have increase vigilance in patients with pain and an ankylosed spine

Presentation

Symptoms
- often asymptomatic and discovered incidentally
- thoracic and lumbar involvement
  - mild chronic back pain
    - usually pain is minimal because of stabilization of spinal segments through ankylosis
  - stiffness
    - worse in the morning
    - aggravated by cold weather
- cervical involvement (with large anterior osteophytes)
  - pain and stiffness
  - dysphagia
  - stridor
  - hoarseness
  - sleep apnea
Physical exam
- decreased ROM of the spine
- neurologic symptoms of myelopathy or spinal stenosis

Imaging

Radiographs
- recommended views
  - AP and lateral spine radiographs of involved region
- findings
  - non-marginal syndesmophytes at three successive levels (4 contiguous vertebrae)
  - thoracic spine
    - radiographic findings on the right side
      - thoracic spine is often involved in isolation
      - particularly T7-T11
      - radiographic examination of this area is helpful when attempting to establish a diagnosis of DISH
  - cervical spine
    - anterior bone formation with preservation of disc space (best seen on lateral cervical view)
    - lateral cervical radiographs useful to differentiate from AS
      - AS will demonstrate disc space ossification (fusion between vertebral bodies)
  - lumbar spine
    - symmetrical syndesmophytes (on left and right side of lumbar spine)
  - other joint involvement e.g. elbow
Technetium bone scan
- increased uptake in areas of involvement
  - may be confused with metastases
CT or MRI
- patients with DISH, neck pain and history of trauma must be evaluated for occult fracture with CT

Differential

	DISH	Ankylosing spondylitis
Syndesmophytes	Nonmarginal	Marginal
Radiographs	"Flowing candle wax"	"Bamboo spine", squaring of vertebral bodies, "shiny corners" at attachment of annulus fibrosus (Romanus lesions)
Disc space	Preservation of disc space	AS in cervical spine will show ossification of disc space
Osteopenia	No osteopenia (rather, there may be increased radiodensity)	Osteopenia present
HLA	No evidence of association with HLA-B27 Associated with HLA-B8 (common in patients with DISH and diabetes)	Strong association with HLA-B27
Age group	Older patients (middle aged)	Younger patients
SI joint involvement	No involvement (SI joint abnormality generally excludes diagnosis of DISH)	Bilateral sacroiliitis
Diabetes	Yes	No

Treatment

Nonoperative
- activity modification, physical therapy, brace wear, NSAIDS and bisphosphonate therapy
  - indications
    - most cases
- cervical traction
  - indications
    - cervical spine fracture
      - use with caution because traction may result in excessive distraction due to lack of ligamentous structures
Operative
- spinal decompression and stabilization
  - indications
    - reserved for specific sequelae (e.g., lumbar stenosis, cervical myelopathy, adult spinal deformity)

Complications

Mortality
- for cervical spine trauma in DISH
  - 15% for those treated operatively
  - 67% for those treated nonoperatively
- higher mortality rates than cervical spine trauma with ankylosing spondylitis
- similar mortality rates to patients with ankylosing spondylitis overall
Heterotopic ossification
- increased risk of HO after THA
  - 30-50% for THA in patients with DISH
  - <20% for THA in patients without DISH