It is a non-inflammatory skeletal disease characterized by calcification and ossification of soft tissues, primarily ligaments and entheses. DISH is also known as senile ankylosing hyperostosis 1).
However, it is now known that this disease is neither limited to the spine nor to older subjects. In 1976, Resnick and Niwayama coined the term “diffuse idiopathic skeletal hyperostosis” (DISH), which is currently widely utilized. Independently of how this condition is named, it consists in a systemic noninflammatory disease characterized by ossification of the entheses – the bony attachment of tendons, ligaments, and joint capsules 2).
This common disorder of unknown etiology is characterized by back pain and spinal stiffness. There may be mild pain if ankylosis has occurred. The condition is recognized radiographically by the presence of “flowing” ossification along the anterolateral margins of at least four contiguous vertebrae and the absence of changes of spondyloarthropathy or degenerative spondylosis. Even in patients who present with either lumbar or cervical complaints, radiographic findings are almost universally seen on the right side of the thoracic spine. Thus, radiographic examination of this area is critical when attempting to establish a diagnosis of DISH. The potential sequelae of hyperostosis in the cervical and lumbar spine include lumbar stenosis, dysphagia, cervical myelopathy, and dense spinal cord injury resulting from even minor trauma. There may be a delay in diagnosis of spinal fractures in a patient with DISH because the patient often has a baseline level of spinal pain and because the injury may be relatively trivial. The incidence of delayed neurologic injury due to such fractures is high as a result of unrecognized instability and subsequent deterioration. Extraspinal manifestations are also numerous and include an increased risk of heterotopic ossification after total hip arthroplasty. Prophylaxis to prevent heterotopic ossification may be indicated for these patients 3).
The disease has about the same frequency in men (65%) and women (35%); it is most common in the thoracic spine and occurs less frequently in the lumbar and cervical spine. The disease most commonly presents in the sixth and seventh decades of life and its estimated frequency in the elderly is 5-15%.
DISH most commonly affects the elderly, especially 6th to 7th decades 4).
The cervical and thoracic (particularly T7-11) 5). spines, in particular, are affected. Additionally, enthesopathy may be identified in the pelvis and extremities.
The aetiology of DISH is still unknown.
Although many external and genetic factors have been reported as being contributors of the pathogenesis of DISH, most of the current theories focus on the pathologic calcification of the anterior longitudinal ligament of the spine. The majority of these theories postulate that this process is due to the abnormal growth and function of the osteoblasts in the osteoligamentary binding 6).
However, it is important to clarify that not all authors accept the association between pathologic calcification and increased bone mineral density 7).
Histopathological features of spinal DISH include :
focal and diffuse calcification and ossification of the anterior longitudinal ligament
paraspinal connective tissue and annulus fibrosis
degeneration in the peripheral annulus fibrosus fibres
anterolateral extensions of fibrous tissue
chronic inflammatory cellular infiltration
periosteal new bone formation on the anterior surface of the vertebral bodies 8).
The condition is commonly identified as an incidental finding when imaging for other reasons.
Spinal hyperostosis can predispose the affected to chronic myelopathic symptoms and acute spinal cord injury.
The involvement of vertebral and extravertebral sites including the pelvis, calcaneum, ulnar olecranon, and patella is frequently found in the literature. The lesions described are the anterior and lateral ossification of the spine, hyperostosis at sites of tendon and ligament insertion, ligamentous ossification, and periarticular osteophytes.
Signs and symptoms include stiffness and pain in the back, dysphagia due to direct esophageal compression/distorsion, pain related to associated tendinitis, myelopathy related to core compression associated to the ossification of the posterior longitudinal ligament, and pain related to vertebral complications–e.g. fracture/subluxation 9).
Neurological complications occur in DISH when the pathological process of ossification extends to other vertebral ligaments, causing ossification of the posterior longitudinal ligaments (OPLL) and/or ossification of the ligamentum flavum (OLF) 10).
Recognised associations include:
Hyperglycaemia 11). approximately one-third of patients tests positive for HLA-B27
The criteria for the diagnosis of diffuse idiopathic skeletal hyperostosis involving the spine are: flowing ossification along the anterior and anterolateral aspects of at least four contiguous vertebrae, preserved intervertebral disc height, no bony ankylosis of the posterior spinal facet joints, and finally no erosion, sclerosis or bony ankylosis of the sacroiliac joints 12) 13).
On imaging, it is typically characterised by the flowing ossification of the anterior longitudinal ligament involving the thoracic spine and enthesopathy (e.g. at the iliac crest, ischial tuberosities, and greater trochanters). There is no involvement of the sacroiliac synovial joints.
While conventional radiography clearly confirms the diagnosis of diffuse idiopathic skeletal hyperostosis, CT and MRI better detect associated findings (e.g. ossification of the posterior longitudinal ligament) and complications (e.g. spinal cord compressive myelomalacia) 14).
DISH involving the spine is identified radiologically by flowing ligamentous ossification and calcification of the anterolateral aspect of the vertebral body with relatively well-preserved disc space of at least four contiguous vertebrae, so-called flowing ossifications 15).
The radiographic criteria, as defined by Utsinger et al., includes:
(1) bridging osteophytes extending over four contiguous vertebral bodies
(2) relatively normal intervening disk space height in relation to height in relation to age
(3) absence of apophyseal joints, bony ankyloses, and absence of erosion, sclerosis, or osseous fusion of the sacroiliac joints 16).
enthesopathy of the iliac crest, ischial tuberosities, and greater trochanters and spur formation in the appendicular skeleton (olecranon, calcaneum, patellar ligament) are frequently present 'whiskering' enthesophytes 17).
Diffuse idiopathic skeletal hyperostosis (DISH) and ankylosing spondylitis (AS) share involvement of the axial skeleton and peripheral entheses. Both diseases produce bone proliferations in the later phases of their course. Although the aspect of these bone proliferations is dissimilar, confusion of radiologic differential diagnosis between the two diseases exists mostly as a consequence of a lack of awareness of their characteristic clinical and radiographic features. The confusion may extend to the clinical field because both advanced DISH and advanced AS may cause the same limitations of spinal mobility and postural abnormalities. However, the radiologic spinal findings are so different that changes due to each disease can be recognized even in patients in whom both diseases occur. This article reviews the clinical and radiologic characteristics that should help clinicians differentiate between the two diseases without much difficulty 18).
syndesmophytes: thinner, form over the annulus, and are vertically oriented (“bamboo spine”)
sacroiliac joint involvement early on and is in the synovial portion (inferior two-thirds)
osteoporosis is prominent
degenerative spine disease
usually has prominent facet and apophyseal joints degenerative changes as well
disc degenerative changes
patients using retinoid acid for skin diseases
predominantly involves the cervical spine
fluorite intoxication due to long-term ingestion
can cause paraspinal ligament calcification
if seen in a child, consider juvenile idiopathic arthritis (JIA)
DISH is generally managed clinically with analgesics and non-steroidal anti-inflammatory drugs when pain and stiffness are related. Possible complications may require specific treatment:
acute spinal fractures
chalk stick fracture
rarely dysphagia caused by mechanical compression due to anterior cervical bone production 19).
DISH rarely causes neurological complications, as evidenced by isolated case reports on the subject; however, if neurological complications do occur, they are often severe enough to warrant major neurosurgical intervention 20) 21) 22) 23).
A retrospective review of patients known to have AS or DISH treated for spinal column fracture at a single institution between 1995 and 2011 was performed. Patients were analyzed by the type of fixation, divided into either a percutaneous group (PG) or an open group (OG). There were 41 patients identified with a spinal column fracture and history of AS or DISH who received surgical intervention. There were 17 (42%) patients with AS and 24 (58%) with DISH. Patients in the PG and OG cohorts presented with similar mechanisms of injury, Injury Severity Scale, number of vertebral fractures, number of additional injuries, and Arbeitsgemeinschaft für Osteosynthesefragen (AO) classification scores. Mean operative time (254.76minutes versus 334.67minutes, p=0.040), estimated blood loss (166.8 versus 1240.36mL, p<0.001), blood transfusion volume (178.32 versus 848.69mL, p<0.001), and time to discharge (9.58 days versus 16.73 days, p=0.008) were significantly less in the PG cohort. The rate of blood transfusion (36% versus 87.5%, p=0.001) and complications (56% versus 87%, p=0.045) were significantly less in the PG cohort. Percutaneous stabilization of fractures in patients with AS or DISH was associated with lower blood loss, shorter operative times and decreased need for transfusion, shorter hospitalization time and a lower perioperative complication rate 24).
Sharma et al. report the results of a retrospective analysis of 74 cases of DISH. Eleven patients presented with progressive spinal cord or cauda equina compression. In nine cases ossified posterior longitudinal ligament (OPLL) and in two cases ossified ligamentum flavum (OLF) were primarily responsible. Surgically treated patients (eight) had far better outcome as compared to the patients managed conservatively, as they had refused surgery. 'DISH' is neither a benign condition, nor it always runs a innocuous clinical course. In fact, in about 15% of the cases, serious neurological manifestations occur, which may require a major neurosurgical intervention 25).
Retrospective evaluation of the osseous pelvis in 93 patients with severe diffuse idiopathic skeletal hyperostosis (DISH) revealed 14 locations of radiographic abnormalities. Two osteoradiologists independently studied these sites for abnormalities in a prospective, blinded fashion in 103 patients over the age of 45 years. Lateral radiographs of the thoracolumbar spine were quantitatively and qualitatively evaluated to determine whether DISH, spondylosis deformans, or a normal spine was present. Statistical analysis was performed for evaluation of interobserver reliability, the relationship between pelvic and spinal abnormalities, and the significance and predictive values of pelvic abnormalities for DISH versus non-DISH and DISH versus spondylosis deformans. Although significantly higher frequencies and greater extents of radiographic abnormalities at 10 of 14 pelvic locations were noted for DISH compared with non-DISH, this number decreased to four of 14 locations when compared with spondylosis deformans. The alterations in three of these four pelvic sites consisted of ossification of ligaments. These changes appear to be good indicators of the presence of spinal DISH and support the concept that DISH is an entity separate from spondylosis deformans 26).
Radiographs of 175 patients with diffuse idiopathic skeletal hyperostosis (DISH) of the spine or ankylosing spondylitis were reviewed. DISH most frequently began in the middle and lower portions of the thoracic spine; it was rare in the upper portion. A few vertebrae were first affected, and then involvement extended, sometimes throughout the thoracic spine. The anterior and lateral aspects of vertebral bodies were mainly affected. Hyperostosis vertically spanning the anterior aspects of the vertebrae varied in thickness up to 10 mm, and the rate at which the hyperostosis proliferated was not specific for any vertebra. Males were 12 times more frequently affected than females, especially in the older age groups. Diabetes mellitus and hypertension have reportedly been associated with DISH, but no such correlation was found in this study. Despite the existence of criteria for differential diagnosis, it is sometimes difficult to distinguish ankylosing spondylitis from DISH radiologically. The radiologic features helpful in the differential diagnosis are described, and a review of the pertinent literature is included 27).
A 78-year-old Japanese man presented with a 6-month history of gait disorder. A magnetic resonance imaging scan of his cervical and thoracic spine revealed anterior spondylolisthesis and severe spinal cord compression at T3 to T4 and T10 to T11, as well as high signal intensity in a T2 weighted image at T10/11. Computed tomography revealed diffuse idiopathic skeletal hyperostosis at T4 to T10. He underwent partial laminectomy of T10 and posterior fusion of T9 to T12. The postoperative magnetic resonance imaging revealed resolution of the spinal cord compression and an improvement in the high signal intensity on the T2-weighted image.
This is the first case of thoracic degenerative spondylolisthesis and spinal cord compression in diffuse idiopathic skeletal hyperostosis. Neurosurgical intervention resulted in a significant improvement of patient's neurological symptoms 28).
A 58-year-old man with diabetes mellitus who did not smoke presented to the hospital with a 12-month history of back pain, progressive numbness in his extremities and difficulty walking. Upon physical examination, the patient had reduced neck motion, bilateral weakness in arm extensors below the elbow, positive Hoffmann sign bilaterally and spastic gait. Radiographic examination showed multilevel contiguous ossification of the anterior longitudinal ligament, ligamentum flavum and posterior longitudinal ligament. We diagnosed diffuse idiopathic skeletal hyperostosis (Figure 1). The patient was treated with a posterior laminectomy and fusion to decompress the spinal cord. His neurologic status improved markedly at six months and remained stable two years after the procedure 29).
Sreedharan et al., report on 3 patients with DISH, who sustained traumatic cervical cord injuries. Two were tetraplegic at presentation. The radiologic findings of the patients are also discussed.
Both the tetraplegic patients were treated non-surgically in view of high surgical risk.
Both the tetraplegic patients died due to mechanical respiratory failure.
The potential catastrophic neurological sequelae of DISH from relatively minor trauma must be understood. Further studies are needed to aid in evidence-based clinical management of asymptomatic patients with DISH 30).
A total of 114 patients undergoing anterior cervical procedures over a 6-year period were included in a retrospective, case-control study. The diagnosis was cervical radiculopathy, and/or myelopathy due to degenerative disc disease, cervical spondylosis, or traumatic cervical spine injury. All our participants underwent surgical treatment, and complications were recorded. The most commonly performed procedure (79%) was anterior cervical discectomy and fusion (ACDF). Fourteen patients (12.3%) underwent anterior cervical corpectomy and interbody fusion, seven (6.1%) ACDF with plating, two (1.7%) odontoid screw fixation, and one anterior removal of osteophytes for severe Forestier's disease. Mean follow-up time was 42.5 months (range, 6-78 months). The overall complication rate was 13.2%. Specifically, we encountered adjacent intervertebral disc degeneration in 2.7% of our cases, dysphagia in 1.7%, postoperative soft tissue swelling and hematoma in 1.7%, and dural penetration in 1.7%. Additionally, esophageal perforation was observed in 0.9%, aggravation of preexisting myelopathy in 0.9%, symptomatic recurrent laryngeal nerve palsy in 0.9%, mechanical failure in 0.9%, and superficial wound infection in 0.9%. In the vast majority anterior cervical spine surgery-associated complications are minor, requiring no further intervention. Awareness, early recognition, and appropriate management, are of paramount importance for improving the patients' overall functional outcome 31).
Association with Retroodontoid synovial cyst has been reported in only one previous study. Cyst probably develop as a result of enhanced mechanical stress on the only remaining mobile joint. In the literature treatment of retro-odontoid mass associated with Forestier has usually involved occipito-cervical fusion with transoral decompression 32).