Diffuse idiopathic skeletal hyperostosis

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Consider a diagnosis of diffuse idiopathic skeletal hyperostosis (DISH) if a person aged over 50 years presents with:

Spinal stiffness/decreased range of motion
Back pain
Stooped posture
Pain and stiffness in other joints.

DISH is gradually progressive with a slow increase in the rate of osteophyte growth.

Symptoms are secondary to new bone formation (the process of calcification and ossification) creating an osteophyte (a small bony bridge or spur), which connects one vertebral body to the next. Spine radiography is the investigation of choice for identifying characteristic bone formation.[24] Bear in mind, though, that DISH is often an incidental finding during routine imaging in patients who are asymptomatic.[1]

Key differentials to consider include ankylosing spondylitis and peripheral osteoarthritis. Note that DISH and osteoarthritis may co-exist in some patients. See Differentials.

History

Take a careful history; specifically ask about the following spine symptoms:

Spinal pain
- In a study of 200 patients with DISH, 72% experienced back pain.[1][9][25]
- The aetiology of the pain is not well understood and may result from either inflammation or bone proliferation.[4]
Stiffness of the spine
- The patient may experience difficulty flexing the spine, leading to functional impairment.[1]
- Morning stiffness of the spine was reported in two-thirds of 200 patients with DISH.[1][9][25]
- Data regarding back pain and stiffness are conflicting, with some reports suggesting that DISH-related spinal fusion may increase the stability of the spine and prevent back pain.[2][26][27]
Stooped posture[9]
- Can in some cases resemble the characteristic posture associated with ankylosing spondylitis.
- It has been postulated that stooped posture may result from abundant new bone formation causing stiffening of the spine, but there are no definitive data to support this hypothesis.
Decreased range of motion
- Reported in approximately 50% of patients with DISH.[9][25]
Spinal fracture[9]
- May, rarely, be the first presenting sign of DISH.
- The ankylosed spine in DISH distorts the previously deformable articulating structures. This deviation prevents the distribution of energy in low-impact trauma that would normally take place in spinal segments and subsequently increases the risk of fractures.[9]
- DISH may also increase the risk of secondary neurological deficits (often as a consequence of the fracture).[9]

Enquire about symptoms of lumbar radiculopathy due to exuberant bone formation and subsequent lumbar spinal stenosis.[28]

Enquire about presence of extraskeletal manifestations of DISH due to cervical enthesophytes, which may include:[1][2][29]

Dysphagia
Dyspnoea
Sleep apnoea
Cervical myelopathy
Cervical radiculopathy
Aspiration pneumonia
Oesophageal obstruction
Stridor
Hoarseness
Thoracic outlet syndrome.

Ask about peripheral joint pain, stiffness, and decreased range of motion.[2] Although hyperostosis was initially reported in the thoracic spine, DISH may affect any skeletal structure to a varying extent.[9][14][30]

There may be involvement of entheses and peripheral joints not typically implicated in osteoarthritis, including the metacarpophalangeal joints, elbows, wrists, shoulders, and ankles.[9][30]
- This is a consequence of ossification and calcification of entheses adjacent to joints.
There are inconsistent findings in the few controlled trials that have evaluated pain in hyperostotic peripheral joints.[31][32] Calcification and ossification of the peripheral entheses in the heels, ribs, and pelvis has also been reported.[9][33][34]
Patients may have poor grip strength, leading to functional impairment.[2][35]
Patients with DISH are more likely to develop heterotopic ossifications in reaction to local events, such as joint replacement surgery, reflecting the systemic bone-forming nature of DISH.[14]

Bear in mind that many patients with DISH are asymptomatic, with ossification often identified incidentally on imaging.[1][2] One hypothesis is that DISH may increase the stability of the spine as a result of the naturally occurring fusion, therefore reducing pain.[2][27]

Enquire about past medical history, including a history of cardiometabolic disease.

Diabetes mellitus, metabolic syndrome, gout/hyperuricaemia, dyslipidaemia, and hypertension are associated conditions and often precede the diagnosis of DISH.[2][16][17]

Risk factors and associated conditions

Key risk factors for developing DISH include:[2][6][7][8][15]

Age >50 years[14]
Male sex
Obesity.

Be aware that diabetes mellitus, metabolic syndrome, and hypertension are comorbid conditions often seen in people with DISH, which may increase cardiovascular morbidity.[2][16][17][36]

Physical examination

Record blood pressure and body mass index (BMI), and consider measuring waist:hip ratio, because metabolic syndrome is commonly associated with DISH.

Perform a careful spine examination, paying particular attention to:

Posture, noting any evidence of kyphosis
Areas of spinal tenderness
Range of motion of the cervical spine and lumbar spine
Signs of radiculopathy (evidenced by a positive straight leg raise test, presence of clonus, spasticity, or a positive Babinski's sign).

As part of the physical examination, also:

Assess for any evidence of spinal fractures, particularly in cases of trauma[1][37]
Assess spinal cord integrity, by assessing neurological function of the arms, legs, bladder, and bowels
Examine peripheral joints for any evidence of bony tenderness or enthesitis
Evaluate gait for any abnormalities or a cautious approach to walking or movement.

Inspection of the back

How to perform an inspection examination of the back, including inspection of gait and posture

Physical examination of the back demonstration

A GP demonstrates how to perform a physical examination of the back

Neurological examination of the back demonstration

A GP shows how to perform a neurological examination of the back

Initial investigations

Spine radiography is the cornerstone of the diagnosis of DISH, although DISH is often an incidental finding during routine imaging.[1]

On radiography, the 'flowing' osteophytes typical of DISH are most likely to be seen on the right anterior thoracic spine, directly across from the pulsating aorta.[1] Pelvic enthesopathies are commonly observed in people with DISH; pelvic insertional tendon enthesopathy is observed as an ossification or calcification of the entheses on pelvic radiographs and on computed tomography (CT).[3]

Radiography

Order plain radiographs if you suspect DISH, based on the patient's history of symptoms and any positive indications after physical examination.

Look for coarse, thick osteophytes that develop mostly on the right side and horizontally along the anterior longitudinal ligament.[4] These findings are often described as having a 'flowing candle wax' appearance. 'Flowing' osteophytes, at a minimum of 3-4 contiguous vertebrae, are a distinguishing feature of DISH.[34][38][39][40]
- There is a lack of universally accepted validated criteria. In practice, 4 continuous flowing osteophytes is generally considered a definitive diagnosis of DISH and 3 is considered probable DISH.
Other characteristic diagnostic features include:[34]
- Preservation of disc height and lack of significant degenerative changes at the involved vertebral segments
- Absence of ankylosis at the facet-joint interface and absence of sacroiliac joint erosion, sclerosis, or fusion.

Bear in mind that DISH frequently co-exists with age-related disc or facet joint degenerative changes, which may be noted on radiographs.[41]

[Figure caption and citation for the preceding image starts]: X-ray images of the thoracic spine of a patient with DISH. (A–C) Posterior–anterior and (D) lateral: large right-sided flowing bridges (white arrows). Note the space between the ligament and the vertebral body (*). Thick flowing ossification of the anterior lateral ligament is shown (black arrow)Mader R, et al. RMD Open 2020; 6: e001151. doi: 10.1136; used with permission [Citation ends]. com.bmj.content.model.Caption@750e842b

Computed tomography (CT)

Although spine radiography is the investigation of choice for identifying characteristic bone formation, CT may also be considered.[4] In particular, CT is useful for detection of early changes secondary to DISH, and is a more sensitive imaging modality than x-ray in showing structural changes; however, this must be weighed against the harm of additional radiation exposure.

Other indications for CT include:

Fracture detection[1][3]
- Request a whole-spine CT scan for patients with suspected spinal fractures.
- It can be challenging to identify spinal fractures in DISH on plain radiographs, due to the presence of degenerative changes and occult fracture lines, and CT can provide a clearer view.
Assessment of dysphagia.[1]

Criteria have been proposed to identify patients with early DISH on CT:[38]

A score from 0 to 3 is assigned for each vertebral segment adjacent to a complete bone bridge, depending on presence of osteophytes, near complete bridging (<2 mm distance between bony structures), and complete bridging (full connection between two adjacent bones with abundant new bone formation).
The presence of <3 adjacent segments with a complete bone bridge is identified as early DISH, while the presence of ≥3 is labelled as definite DISH.[38]

[Figure caption and citation for the preceding image starts]: CT images of the thoracic spine in DISH. (A–C) Sagittal: CT scan images of anterior flowing osteophytes (arrows). (D) Coronal: dish of the thoracic spine (arrow) reconstructed from the chest CT scan. L = leftMader R, et al. RMD Open 2020; 6: e001151. doi: 10.1136; used with permission [Citation ends]. com.bmj.content.model.Caption@7053cdcc

Other investigations

Tailor subsequent diagnostic testing to suspected areas of spinal or extraspinal involvement. This may include imaging, such as x-ray or CT of the cervical spine or lumbar spine (if not previously obtained), or x-ray of peripheral joints.[4] Imaging of additional spinal segments is recommended in cases of suspected fractures.[1] Magnetic resonance imaging (MRI) can detect occult fractures, particularly in patients with neurological deficits.[1] Musculoskeletal ultrasound can be used for evaluation of entheseal changes in peripheral joints.[42]

In cases of soft-tissue involvement secondary to osteophytes, consider a swallow study or refer to an otolaryngologist or gastroenterologist.

Consider pulmonary function testing in patients with suspected restrictive lung disease, as there may be an association between DISH and pulmonary function abnormalities.[43] A restrictive spirometry pattern with evidence of extrathoracic obstruction was noted in one study of a cohort of heavy smokers with DISH.[43]

Consider dual-energy x-ray absorptiometry (DXA)/whole-spine vertebral fracture assessment (VFA) in patients with fracture secondary to DISH. Note that ossification of ligaments and formation of bony bridges in patients with DISH can be mistaken for increased bone density by the DXA scan; consider testing with quantitative computed tomography (QCT) as an alternative to DXA, which can differentiate between cortical and trabecular bone.[44]

Blood tests, such as erythrocyte sedimentation rate, C-reactive protein, HLA-B27, rheumatoid factor, and antinuclear antibody levels, are recommended to help exclude differentials such as ankylosing spondylitis; note, results are frequently normal in patients with DISH. Also consider screening for metabolic disorders that are commonly associated with DISH, such as diabetes and hyperlipidaemia. See Type 2 diabetes in adults, Hypercholesterolaemia, and Metabolic syndrome.

Sclerostin and parathyroid hormone are emerging as biomarkers that are possibly associated with DISH. The bone turnover marker sclerostin has been studied in women with type 2 diabetes with and without DISH, and has been noted to be lower in patients with DISH.[1][16] Levels of parathyroid hormone may also be low in patients with DISH.[45]

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