Diffuse Idiopathic Skeletal Hyperostosis (DISH)

Diffuse idiopathic skeletal hyperostosis (DISH) was first described in 1948 by Forestier and Rotes-Querol in a report on nine patients, ranging in age from 50 to 73 years, who suffered from spinal rigidity and had exuberant osteophytes on radiologic studies. These authors termed the condition senile vertebral ankylosing hyperostosis.[5]

DISH is well represented in the zoologic and paleontologic record. It is found in 1-3% of baboons and monkeys, as well as in gorillas, bears, camels, horses, bison, musk oxen, canids, felids, and whales[6, 7, 8, 9, 10, 11, 12] ; DISH was also present in dinosaurs.[13, 14, 15] An age-dependent phenomenon, it occurs in 15-25% of older mammals.

Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by a tendency toward ossification of ligament, tendon, and joint capsule (enthesial) insertions.[16] DISH is often a completely asymptomatic phenomenon, with no alterations detectable based on history or through physical examination.

Causes are unknown. Diffuse idiopathic skeletal hyperostosis (DISH) is simply a tendency toward calcification of entheses.

Epidemiologic studies have identified a range of risk factors for DISH, with higher rates seen with age over 50 years, in men compared with women, and in the White population compared with Black, Asian, and Native-American populations.[4]  Additional risk factors include the following[17] :

• Obesity
• Hypertension
• Metabolic syndrome
• Type 2 diabetes mellitus
• Hyperuricemia

Lantsman et al reported that abdominal computed tomography showed significantly more visceral adipose tissue, as well as a significantly higher ratio of visceral to subcutaneous adipose tissue, in 43 patients with DISH as compared with 42 controls. These authors note that visceral adipose tissue is by itself associated with bone proliferation, and suggest that it is potentially a pathogenic pathway for enthesopathic excessive bone production in DISH.[18]

Frequency

United States

Diffuse idiopathic skeletal hyperostosis (DISH) is present in approximately 19% of men and 4% of women older than 50 years. Frequency information in the US was derived from the study of nonselected skeletal/cemetery populations.[19]

International

In a study by Mori et al of 3013 Japanese patients (1261 females and 1752 males) with a mean age of 65 years, the computed tomograph– based prevalence of thoracic DISH was 8.7%.[20] The posterior longitudinal ligament of the cervical spine is ossified in 2% of Japanese individuals but in only 0.16% of white persons.[21] The anterior longitudinal ligament is calcified in 24% of patients with posterior longitudinal ligament ossification.[22]

DISH was reported in 17% of individuals in the Netherlands, paradoxically with male predominance.[23] A South African study of hospitalized patients 40 years of age and older found that the prevalence of DISH in African blacks was 3.8% in men and 4.2% in women; the prevalence rose with increasing age, from 1% in the 40-49 year age group to 13.6% in those over 70 years.[24]

Race-, sex,-, and age-related demographics

DISH is present in approximately 19% of men older than 50 years but is found in only 4% of women in this age group. It is uncommon in patients younger than 50 years and is extremely rare in patients younger than 40 years.

A study from Finland[25] revealed the age frequency in Finnish men to be as follows:

• 40-49 years - 0.3%
• 50-59 years - 2.7%
• 60-69 years - 8.4%
• 70 years or older - 11.2%

The same study revealed the age frequency in Finnish women to be as follows:

• 40-49 years - 0.2%
• 50-59 years - 1.7%
• 60-69 years - 4.3%
• 70 years or older - 6.9%

In a study of community-dwelling men (n = 630) and women (n = 961), mean age 71.5 years, from the Rancho Bernardo Study, DISH was present in 25.6% of men and 5.5% of women.[26]

A study of middle-aged and elderly people randomly sampled from the resident registry of a rural town in Japan identified DISH in 72 (17.5%) of the 413 participants. The prevalence of DISH tended to increase with age, from 3.1% in subjects in their 50s to 14.0% in those in their 60s, 24.3% in those in their 70s, and 29.0% in those in their 80s. In addition to aging, other independent factors associated with DISH were hypertension (odds ratio [OR] 1.93), male sex (OR 2.88) and elevated body mass index (OR 19.1).[27]

Patients with diffuse idiopathic skeletal hyperostosis (DISH) have an excellent prognosis, as the condition is rarely life-threatening and causes limited morbidity.

DISH appears to be a phenomenon rather than a disease. A double-blind controlled evaluation (in which controls and patients were drawn from the same population) revealed no associated pathology. Arthritis, bursitis, and tendinitis appeared no more frequently in patients with DISH than in controls. Any back pain present was no different in character or duration than that noted in control subjects. A history of back injury was actually found to be twice as frequent in control subjects as it was in patients with DISH. Back flexibility was no more limited in patients with DISH than it was in controls. In fact, patients with DISH who had decreased lumbar spinal motion had a lower frequency of back pain, implying that DISH may be protective.[19, 28]  One study has showed that DISH may be protective against back pain.[29]

In another study, people with DISH were more likely to experience physical functional impairment. This included 1.72-fold increased odds of self-reported difficulty bending; worse grip strength; and in men only,  2.17-fold increased odds of being unable to complete 5 chair stands without using their arms.[26]

A study of 1063 patients treated surgically for lumbar spinal stenosis found that reoperations were performed significantly more often in patients with DISH that extended to the lumbar segment: 22% of such patients underwent reoperation, compared with 7.3% of patients without lumbar DISH (P < 0.001). The authors suggest that the unfavorable outcomes in patients with lumbar DISH may be due to the decreased number of lumbar mobile segments.[30]

Overgrowth of ligamentous calcification could impinge on other structures (eg, the esophagus). Reports of this are rare and often represent inadvertently discovered, neurologically mediated swallowing deficits.[31, 32]   Compression of the larynx leading to vocal cord paresis and airway obstruction has been reported.[33]

Posterior longitudinal ligament ossifications may impinge on the spinal cord on rare occasions.

Reduced vertebral column flexibility predisposes to vertebral fracture. Vertebral fracture risk (cervical, 60%; thoracic, 34.5%; lumbar, 5.5%) is inherent with an ankylosed hyperostotic vertebral column from minor trauma, preoperative and postoperative positioning, or intraoperative maneuvers (eg, retroperitoneal or hip replacement surgery).[3, 34, 35]  Note that as well as with fully ankylosed spines, partially ankylosed spines also are at risk, with fractures occurring adjacent to the fused regions.[36]  The risk of fracture increases with the number of vertebra ankylosed.[37]  Obesity is an additional risk factor for fracture,[38]  overstressing the already at-risk spine.

Diffuse idiopathic skeletal hyperostosis (DISH) is often an asymptomatic phenomenon that is discovered incidentally on imaging studies taken for some other reason. Reported manifestations, which may result from neuropathy or from physical impingement by bony overgrowth, have included the following[1] :

• Polyarticular pain
• Neck/thoracic/lumbar/extremity pain
• Acute monoarticular synovitis
• Limited range of spinal motion
• Dysphagia ^[39]
• Increased susceptibility to unstable spinal fractures
• Airway obstruction of varying degrees

If vertebral fusion is quite extensive, reduction in range of spinal motion occurs.[40] Because uniform vertebral involvement is extremely rare, no relatable findings exist.

No laboratory tests are indicated. An apparent association with elevated glucose levels has not been substantiated as a relationship with diabetes.[41, 42]

Diffuse idiopathic skeletal hyperostosis (DISH) involves the thoracic vertebrae in 100% of cases, the lumbar vertebrae in 68-90%, and the cervical vertebrae in 65-78%. Ligamentous ossification affects both sides of the lumbar vertebral column but tends to be unilateral in the human spine.

Prominence of DISH on the right lateral aspect of the thoracic spine is apparently related to aortic pulsations. Left-sided overgrowth is much reduced, also probably because of the influence of aortic pulsations, an idea supported by the notation of left-sided prominence in individuals with situs inversus (left-sided thoracic aorta).

The earliest sign of DISH appears to be new bone formation adjacent to the midportion of the vertebral body, a phenomenon often below the limits of radiologic detection. Recognition of DISH is facilitated by its separation from the body of the vertebrae. Radiologically, this appears as a radiodense line paralleling the longitudinal axis of the spine but separated by a clearly definable space.

The most commonly used diagnostic criteria for DISH are those set by Resnick and Niwayama, which are as follows[43, 44] :

• Calcification and ossification along the ventrolateral aspects of at least four contiguous vertebral bodies, with or without localized pointed excrescences at intervening vertebral body–disk junctions
• Relative preservation of intervertebral disc height in the involved areas, with absence of extensive radiographic changes of degenerative disc disease (intervertebral osteochondrosis), including vacuum phenomena and vertebral body marginal sclerosis
• Absence of apophyseal joint bony ankylosis and sacroiliac joint erosion, sclerosis, or intra-articular bony fusion

Criteria suggested by Julkunen and colleagues are substantially the same as those from Resnick and Niwayama, but also include the presence of bridges connecting two vertebral bodies in at least two sites on the thoracic spine.[45] Utsinger criteria are as follows:

• Definite DISH: Bridging of four contiguous vertebral bodies, primarily in the thoracolumbar spine, minimal intervertebral disk disease, and no facet joint ankylosis
• Probable DISH: Bridging of two contiguous vertebral bodies plus bilateral patellar tufting, heel spurring, and olecranon tufting.
• Possible DISH: Two vertebrae joined in the absence of extraspinal enthesophytes, or symmetrical extraspinal enthesophytes in the absence of spinal involvement

The general term DISH emphasizes that the ligamentous ossification phenomenon is not limited to the spine. Exuberant ossification at sites of tendon, ligamentous, or joint capsule insertion (enthesitis) is strongly suggestive of the diagnosis. A tendency toward such ossification at any site of ligament and perhaps tendon insertion appears to exist. One study found pelvic enthesopathy on CT to be significantly more prevalent in patients with DISH compared with matched control patients.[46]

Enthesial reaction at the iliac crest and ischial tuberosities often is referred to as pelvic whiskering and typically is quite exuberant. Such whiskering was noted in two thirds of iliac crests studied and in 53% of ischial tuberosities. Enthesial reaction was noted in 42% of lesser and 36% of greater trochanters of the femur. Enthesial spurs at the site of insertion of the quadriceps mechanism into the patella were present in 29% of patients studied. Osseous bridging of fibula and tibia was noted in 10% of patients. Distal metacarpal and phalangeal capsular hyperostosis were present in 13% of patients with DISH.[19]

Katzman et al reported that DISH is associated with greater kyphosis in older men and women. However, DISH was not significantly associated with a change in kyphosis over 4-5 years, and in women followed over 15 years, those with DISH had less progression of kyphosis than those without DISH.[47]

Whole-spine computed tomography (CT) is mandatory in patients with DISH who have experienced low-impact trauma, according to Lantsman and colleagues, because the rigid spinal structure resulting from DISH increases susceptibility to spinal fracture, and radiographs have low specificity for detecting those fractures. In their study of 147 patients with verified DISH who presented to the emergency department after low-energy trauma, significantly more acute fractures were evident on whole-spine CT than on radiographs (55 versus 32, respectively; P < 0.00001).[48]

These authors also found that in 57% of all acute fractures, the site of tenderness was not indicative of the fractured spinal segment. In addition, two patients with tenderness at the site of one fracture also had asymptomatic distant fractures.[48]

For complete discussion, see Imaging in Diffuse Idiopathic Skeletal Hyperostosis (DISH).

Histologic examination of vertebral specimens from patients with diffuse idiopathic skeletal hyperostosis (DISH) show partial or complete bone bridges consisting of cortical haversian bone, accompanied by morphological changes in the adjoining part of the intervertebral disc.[49] Ossified tissues in DISH are composed of normal-appearing haversian bone, as opposed to the wormian or disorganized structure of bone seen in patients with hypervitaminosis A.[50]

No cure for diffuse idiopathic skeletal hyperostosis (DISH) exists. Therapy is symptomatic and empirical, and may include measures such as the following[2] :

• Physical therapy
• Analgesics
• Sedation
• Anti-inflammatory drugs
• Muscle relaxants

Successful treatment of dysphagia with nighttime continuous positive airway pressure (CPAP) therapy has been reported.[51]

Surgery may be indicated to provide relief of severe symptoms, such as airway obstruction or dysphagia, that have not responded to conservative treatment.[2]  Although tracheotomy is the treatment described in most cases of DISH-related airway obstruction in the literature, Yosimatsu et al report a case of successful treatment with careful airway management and surgical osteophytectomy.[52]