Laboratory Studies
No laboratory tests are indicated. An apparent association with elevated glucose levels has not been substantiated as a relationship with diabetes. [41, 42]
Imaging Studies
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] :
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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
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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
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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:
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Definite DISH: Bridging of four contiguous vertebral bodies, primarily in the thoracolumbar spine, minimal intervertebral disk disease, and no facet joint ankylosis
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Probable DISH: Bridging of two contiguous vertebral bodies plus bilateral patellar tufting, heel spurring, and olecranon tufting.
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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 Findings
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]
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Radiograph of the thoracic spine (anteroposterior view) showing osteophytes on the right side only, a feature typical of diffuse idiopathic skeletal hyperostosis.
