Diffuse idiopathic skeletal hyperostosis (DISH), also known as Forestier disease, is a common condition characterised by bony proliferation at sites of tendinous and ligamentous insertion. It primarily affects the spine of older individuals. On imaging, it manifests as flowing bridging anterior vertebral osteophytes, most prominent in the thoracic spine, and enthesopathy particularly around the pelvis. The presence of flowing anterior ossification spanning at least four vertebral levels with preserved disc spaces is often used to define the disease.

Epidemiology

DISH is more common with increasing age ²³, and is most common in the 6^th to 7^th decades ³. The estimated prevalence is ~15% (range 3-42%) with a male predominance ^6,23,24. The prevalence appears higher in developed countries.

Risk factors

• chronic isotretinoin use (retinoid medication used for cystic acne) ²⁶

Diagnosis

The Resnick and Niwayama criteria remain the most widely used in the imaging diagnosis of DISH (c. 2021 ²⁴), requiring ¹⁹:

• flowing osteophytes over at least four contiguous vertebrae of the thoracic spine

• preservation of intervertebral disc space without extensive degenerative intervertebral disease

• absence of facet and costovertebral joint ankylosis

• absence of sacroiliac joint (SIJ) erosion, sclerosis or fusion*

However, this represents end-stage DISH and others ^ref have suggested using a vertebral span of three or even two levels in the setting of prominent extra-spinal enthesopathy. Other criticism includes that only axial manifestations form part of these criteria ²⁴.

*NB SIJ enthesophytes have subsequently been shown to common in patients with DISH ²².

Clinical presentation

DISH is often asymptomatic and identified as an incidental finding on imaging performed for other reasons ²³. However, back pain and spinal stiffness are common symptoms in patients with DISH although it is unclear if this is specific to the diagnosis of DISH ²³. Similar symptoms of pain and stiffness in the peripheral joints have been reported ²³.

When DISH affects the cervical spine, dysphagia, airway obstruction, and/or difficult tracheal/oesophageal intubation may occur from mechanical compression due to anterior cervical bone production upon the hypopharynx and upper oesophagus ^22,23.

Spinal fractures, following even low impact trauma, may be a presenting scenario if DISH results in spinal ankylosis ²³.

Pathology

The aetiology of DISH is unknown (c. 2020) ²³ but likely involves an imbalance of growth factors and inhibitors leading to excessive bone formation. Histopathological features of spinal DISH include ⁵:

• focal or diffuse calcification and/or ossification of the anterior longitudinal ligament

  • controversial as some studies have shown ALL not to be involved ²³

• ossification of the paraspinal connective tissue and annulus fibrosus

• degeneration of the peripheral annulus fibrosus fibres

• anterolateral extensions of fibrous tissue

• hypervascularity

• chronic inflammatory cellular infiltration

• periosteal new bone formation on the anterior surface of the vertebral bodies

The rate at which the ossification progresses is reported to be around one vertebral space bridged every 10 years ¹⁴. The bone outgrowth begins at the anterior vertebral body above and below the disc.

Location

• thoracic spine (most common) ²²

  • right anterolateral ossifications: particularly T7-T11 ⁵

  • descending aortic pulsation prevents it on the left (opposite occurs if there is situs inversus)

• cervical spine: anterior ossification, maximal at lower half of vertebral body

• lumbar spine

  • upper lumbar segments commonly involved ²²

  • osteophytes are usually bilateral ²²

  • implies advanced/late disease

• pelvis (common) ²²

  • sacroiliac joints: bridging osteophytes located ventrally

  • pelvic enthesophytes are thought to be highly characteristic ²²

    • gluteus medius origin at the iliac crest and insertion at the greater trochanter

    • adductor complex origin at the symphysis pubis

    • hamstring complex origin at the ischial tuberosity

• appendicular skeleton

  • enthesophytes around the knee, elbow, ankle ²²

  • involvement of peripheral (e.g. elbow, metacarpophalangeal, glenohumeral) joints not usually affected by osteoarthritis ²²

Associations

• ossification of the posterior longitudinal ligament: in ~50% of cervical DISH cases ¹³

• metabolic syndrome, hypertension, obesity and diabetes mellitus ²³

• ossification of the stylohyoid ligament and Eagle syndrome: DISH and ankylosing spondylitis patients both have measurably longer styloid process than controls ¹⁶

• ankylosing spondylitis: can be both a co-existing condition and differential diagnosis ²²

Radiographic features

Plain radiograph and CT

Spinal features

• flowing ossifications

  • florid, flowing ossification along the anterior or right aspects of at least four contiguous vertebrae ^7,22

  • the left lateral aspect is usually spared in the thoracic spine, thought due to aortic pulsation inhibiting ossification ⁵

• osteophytes are largely paraspinal with a linear lucency often seen between the anterior vertebral body cortex and the osteophyte ²²

  • this helps distinguish DISH from degenerative endplate osteophytes and from the syndesmophytes of ankylosing spondylitis ²¹

• disc spaces are usually well preserved: osteophytes/ossification is out of proportion to the degree of disc degeneration ²²

• resultant ankylosis and rigidity is more common in the thoracic than cervical or lumbar spine

  • frequently incomplete ²²

  • can have interdigitating areas of protruding disc material in the flowing ossifications

• no facet joint of costovertebral ankylosis although entheseal bridging may be present ¹⁷

• chunky ossifications from the lower anterior half of the vertebral body in the cervical spine have been described as being like a candle flame, fall drop, or parrot-beak ²²

Sacroiliac features

• no sacroiliitis or erosions, however bridging osteophytes anterior to the sacroiliac joints, similar to flowing osteophytes in the spine, are common

• posterior bridging osteophytes occur less commonly

• the bridging osteophytes may mimic joint ankylosis on x-ray

Extraspinal features

• enthesopathy of the iliac crest, ischial tuberosities, and greater trochanters

• prominent pelvic enthesophytes are strongly associated with DISH ¹⁶

• exuberant spur formation in the appendicular skeleton (olecranon, calcaneum, patellar tendon) frequently present

• 'whiskering' enthesophytes

• peripheral joint manifestations including epiphyseal enlargement and joint space narrowing ²²

MRI

• findings correspond to those on CT

• typically true ossification with marrow signal

• fat metaplasia at the vertebral corners, and to a lesser degree bone marrow oedema, may occur in DISH, but this is less common than in ankylosing spondylitis ¹⁸

Treatment and prognosis

DISH is generally managed symptomatically with analgesics, such as non-steroidal anti-inflammatory drugs, when pain and stiffness are related ²³. Managing comorbid conditions like obesity and diabetes mellitus is important.

Complications

Possible complications may require specific treatment: 

• spinal stenosis ²²

• acute spinal fractures, in particular chalk stick fracture, in low impact trauma

  • inspect the ossified ligaments for disruption, and compare with prior imaging where available to discern fracture from a region without ossification

  • note that fractures can also occur above or below the rigid segment due to altered biomechanics

• dysphagia: resection of osteophytes can relieve mechanical symptoms ²³

• cervical DISH can make intubation more difficult ^11,22

• lumbar DISH can cause radiculopathy ¹¹

Differential diagnosis

• ankylosing spondylitis

  • syndesmophytes: thinner, form over the annulus, and are vertically orientated ("bamboo spine") 

  • true sacroiliitis involving the synovial joint (inferior two-thirds) with erosions, adjacent marrow oedema/fat metaplasia and eventual intra-articular ankylosis, as opposed to the para-articular bridging osteophytes seen in DISH

  • osteoporosis is prominent

  • may co-exist with DISH ²²

• spinal degeneration (spondylosis)

  • disc degeneration and height loss

  • osteophytes arise from the endplates rather than anterior cortex/paraspinal location

  • anterior longitudinal ligament uncommonly ossified in degenerative disease alone ⁹

  • prominent facet and apophyseal joints degenerative changes

• retinoid arthropathy 

  • patients using retinoid acid for skin diseases

  • skeletal hyperostosis 

  • predominantly involves the cervical spine

• fluorosis

  • fluorite intoxication due to long-term ingestion

  • can cause paraspinal ligament calcification

  • will have accompanying osteosclerosis, or trabecular blurring/haziness

• if seen in a child, consider juvenile idiopathic arthritis (JIA)