Diffuse idiopathic skeletal hyperostosis (DISH) is a condition characterised by calcification and ossification of ligaments and entheses. The condition usually affects the axial skeleton, in particular, at the thoracic segment, though also other portions of the spine are often involved. DISH often involves also peripheral tendinous and/or entheseal sites either alone, or in association with the involvement of peripheral joints. At times, new bone formation involves the bone itself, but sometimes it involves joints not usually affected by osteoarthritis (OA) which result in bony enlargement of the epiphysis, joints space narrowing and a reduced range of motion. Because of the entheseal involvement, DISH can be mistaken for seronegative spondyloarthropathies or for a "simple" OA. Furthermore, other implications for the recognition of DISH include spinal fractures, difficult intubation and upper endoscopies, decreased response rates in DISH with concomitant spondyloarthritides, and increased likelihood to be affected by metabolic syndrome and cardiovascular diseases. This Atlas is intended to show the imaging finding in DISH in patients diagnosed with the condition by the Resnick classification criteria.
- ankylosing spondylitis
- hand osteoarthritis
- knee osteoarthritis
- orthopaedic surgery
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What is already known about this subject?
DISH is a relatively common musculoskeletal condition appearing in the rheumatology practice
Although the clinical symptoms are common to other musculoskeletal diseases, the diagnosis is mainly being made using images of the axial and the peripheral skeleton
What does this study add?
We here present a comprehensive imaging Atlas of various, common and rare manifestations of DISH
How might this impact on clinical practice?
This Atlas may help clinicians in daily practice as reference of unclear images of patients who present with clinical symptoms suggestive of DISH and where imaging may be inconclusive.
Diffuse idiopathic skeletal hyperostosis (DISH), is a condition characterised by calcification and ossification of ligaments and entheses. The condition usually affects the axial skeleton, in particular at the thoracic segment though also other portions of the spine are often involved. DISH often involves also peripheral tendinous and/or entheseal sites either alone, or in association with peripheral joints' involvement.1 At times, new bone formation involves the bone itself, but sometimes it involves joints not usually affected by osteoarthritis (OA), which result in bony enlargement of the epiphysis, joints space narrowing and a reduced range of motion.2 Because of the entheseal involvement, DISH can be mistaken for seronegative spondyloarthropathies or for a ‘simple’ OA.3 Furthermore, other implications for the recognition of DISH include spinal fractures, difficult intubation and upper endoscopies, decreased response rates in DISH with concomitant spondyloarthritides, and increased likelihood to be affected by metabolic syndrome and cardiovascular diseases. This atlas is intended to show the imaging finding in DISH in patients diagnosed with the condition by the Resnick classification criteria.1
In the initial stages of the disease, small bony areas in front of the disk space can be observed in the sagittal projection. Then, laminar ossifications appear in the medial–inferior and medial–superior portion of the anterior and lateral vertebral margins. In the following stages, enthesophytes do elongate and thicken, especially on the anterior and right sides of the vertebral bodies. Between the newly formed bone and the anterior border of the vertebral body, a ‘linear radiolucency’ may be detected. Involvement of the T-spine is probably the most characteristic radiographical finding. Ankylosis is often incomplete.4
The upper lumbar segments are involved in a large percentage of cases. Radiographical abnormalities along the anterior aspect of the lumbar spine are similar to those of the cervical spine. Unlike the thoracic spine, the flowing ossifications are equally frequent on the right and left sides of the lumbar spine. One can observe ossifications of the spinous processes and of the interspinous ligaments. The narrowing of the intervertebral space is generally classified as mild to moderate. Degenerative changes in apophyseal joints can occur in the lower lumbar spine and in the lumbosacral junction too. Due to the hyperostosis, spinal stenosis is not rare.5
The hyperostotic process develops along the lower half of the anterior border of the vertebral body: morphological aspects are described appears as ‘falling drop’ or as prevertebral drop at the front of the vertebrae. Subsequently, these kind of ‘drops’ tend to grow, forming spurs (enthesophytes) until they band together; then, the spurs expand on the superior and anterior tracts of the underlying vertebral body, leading in turn to the formation of ‘candle flame’, ‘parrot-beak’ image or ‘bridge’. The cervico-occipital junction may be involved with the vertebral bodies showing increased diameters due to bone neoapposition along the margins. At times, the hyperostotic process may involve the odontoid process and the adjacent ligaments.1
Peripheral involvement in DISH is characterised by several distinctive features:
Involvement of joints usually unaffected by primary OA, such as the elbows, metacarpophalangeal joints, shoulders and others.
Increased hypertrophic changes compared with primary OA. Prominent enthesopathies at various sites adjacent to peripheral joints, including entheseal insertions of joints' capsules, and tendons attachments. Calcification and ossification of entheses in sites other than joints such as the tibial tuberosity, olecranon, Achilles insertion and plantar fascia.2
DISH and ankylosing spondylitis (AS)
DISH and AS are the prototypes of hyperostotic diseases of the axial skeleton.6 The bone proliferation leads in the long term to ankylosis of the spine and functional impairment. Similarly, due to the local osteoporosis and decreased flexibility of the affected bones, vertebral fractures are frequent in both DISH and AS even after minor impact traumata.7 Beyond clinical and genetic differences, the phenotype of new bone formation is different between the diseases. In DISH, the so-called ‘chunky bridging osteophytes’ which grow as an additional layer on the anterior longitudinal ligament are typical, while in AS, the frequently thinner, marginal and symmetrical syndesmophytes which represent an ossification of enthesitic lesions at the area of the attachment of the anterior longitudinal ligament and the annulus fibrosus are more common.6 Although initially DISH and AS were thought to be distinct conditions, recent studies have also reported the simultaneous presence of both diagnoses in some patients.8 Structural changes of the spine and the SIJ may occur in DISH and AS. Therefore, MRI sequences may be helpful differentiating the two diseases as, in addition to structural damage, MRI may show inflammatory changes with the typical pattern of AS. In addition, especially in younger patients, radiation exposure also needs to be considered, making MRI a useful tool in this diagnosis.
Pelvis in DISH
The pelvis is one of the main extraspinal involved sites in DISH and was therefore suggested to be included in future classification criteria for DISH.
Pelvic enthesopathies are considered highly characteristic of DISH and have been shown to be significantly more prevalent and more prominent in DISH subjects compared with controls.9 Indeed, pelvic insertional tendon enthesopathy on pelvic radiographs and on CT, seen as an ossification or calcification of the entheses, has been found to be a good indicator of the presence of radiographical spinal DISH.10 11 Among the main involved pelvic entheses are the origin of the gluteus medius along the iliac crest, the origin of the adductors on the symphysis pubis, the hamstrings origin on the ischial tuberosity and insertion of the gluteus medius on the greater trochanter.
The sacroiliac joints (SIJs) are of main interest in DISH. On one hand, the Resnick and Niwayama criteria exclude their involvement in order to differentiate DISH from AS,12 but on the other hand, recent studies have shown that enthesopathy is also highly abundant in the SIJs of DISH subjects.13 Indeed, erosions are seldom seen in DISH and indeed differentiate it from AS.11 However, enthesopathy of the anterior and posterior ligaments and capsule of the SIJs, as well as bridging, fusing enthesophytes within the joints mimicking joint ankylosis of AS, have been shown to be characteristic of DISH.6 Some preliminary MRI studies have described bone marrow oedema in the SIJs of DISH subjects; however, this observation needs further in-depth evaluation and characterisation.12
DISH and spinal fractures
The osseous bridges connecting vertebral bodies ventrally in DISH may cause stiffening of the spinal column, thereby changing biomechanical characteristics. Although appearing robust with the abundantly formed bone, the spinal column in individuals with DISH is actually more prone to fractures compared with non-affected individuals. Fractures may occur after only minor or trivial trauma, are often severely displaced and are frequently accompanied by neurological deficits due to associated spinal cord injury.13 14 Identifying spinal fractures in individuals with DISH can be challenging due to the radiological presence of degenerative changes, occult fracture lines (although these lines typically run all the way front to back through the spinal segments), and patients not always being able to distinguish between pre-existent and new pain in the back and/or neck. With plain radiographs, spinal fractures in DISH can be easily missed; therefore, a CT scan of the entire spinal column is recommended if a fracture is suspected. MRI scans are helpful in case of suspicion of occult fractures that are difficult to detect with CT.15 Hyperextension is the predominant fracture mechanism in DISH (Arbeitsgemeinschaft für Osteosynthesefragen (AO) type B3), a configuration which generally requires long-segment surgical fixation to provide sufficient mechanical stability to allow for fracture healing and prevent (further) neurological deficits. Patients not fit for surgery may be treated conservatively with collar or brace, but some evidence exists showing the complication rates to be higher in non-operatively treated patients when compared with patients undergoing prompt surgical fixation.16
X-ray images of the thoracic spine are shown in figure 1.
CT images of the thoracic spine are shown in figure 2.
A magnetic resonance image of the thoracic spine is shown in figure 3.
X-ray images of the lumbar spine are shown in figure 4.
A CT image of the thoracic spine is shown in figure 5.
Magnetic resonance images of the lumbar spine are shown in figure 6.
X-ray images of the cervical spine are shown in in figure 7.
CT images of the cervical spine are shown in figure 8.
Magnetic resonance images of the thoracic spine are shown in figure 9.
Peripheral joint involvement
X-ray images of small joints are shown in figure 10.
Peripheral joint involvement
X-ray images of large joints are shown in figure 11.
Enthesopathies in DISH
X-ray and CT images of enthesopathies are shown in figure 12.
DISH and AS
DISH and AS in X-ray and CT are shown in figure 13.
Changes in the pelvis in DISH
X-ray changes in the pelvis in DISH are shown in figure 14.
CT changes in the pelvis in DISH are shown in figure 15.
MRI changes in the pelvis in DISH are shown in figure 16.
Contributors All authors collected the images, agreed on the content, and revised and approved the manuscript. All Authors contributed with images and/or comments to the entire imaging collection of this Atlas.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information. There are no data to serve as a background of this article.