Diffuse Idiopathic Skeletal Hyperostosis

Diffuse idiopathic skeletal hyperostosis (DISH), also previously known as Forestier disease, is a disorder of unknown etiology that was first described in 1950 by Forestier and Rotes-Querol and termed senile ankylosing vertebral hyperostosis. However, the disease is not limited to the elderly nor is it isolated to the spine, with extraspinal manifestations being common. Resnick and Niwayama thus suggested a change in terminology to diffuse idiopathic skeletal hyperostosis.

To assist in diagnosis and allow for further investigation, Resnick and Niwayama determined specific criteria, as listed in Box 100-1 . The first criterion defines DISH as flowing osteophytes along the anterolateral border of the vertebral body at four contiguous spinal levels. Criteria 2 and 3 eliminate other possible etiologies of this radiographic finding, allowing for no degenerative changes and no ankylosis of the facet or sacroiliac joints. Mata and colleagues subsequently developed a scoring system to quantify involvement.

DISH is characterized by significant calcification and subsequent ossification of the entheses, particularly, but not limited to, the thoracic spine with preferential involvement of the anterior longitudinal ligament.

The presence of hyperostosis suggests possible links to similar ankylosing or rheumatologic diseases, but no connection has been noted to date, including no association with human leukocyte antigen (HLA)-B27, a common marker for ankylosing spondylitis. Though no genetic factors have yet been identified, the focal distribution of disease suggests a genetic link exists as such. Research from the Osteoporotic Fractures in Men (MrOS) study demonstrated a high prevalence in men, 42%, increasing with age from 50 to 80 years. In addition, DISH was highly associated with higher body mass index (BMI) and hypertension compared to those without the disease. The association with higher BMI was corroborated along with additional factors noted such as diabetes and hyperuricemia in a case control study by Kiss and coworkers. Metabolic factors, including hyperlipidemia and hypervitaminosis A, have also been implicated as part of a metabolic syndrome including DISH. Another possible factor was suggested in a pathologic study —hypervascularity via increased number and width of nutrient foramina, which resulted in increased size of the vertebrae as well.

The exact prevalence of DISH is unclear. As previously mentioned, MrOS noted a prevalence of 42%. An autopsy series of 75 spines performed by Boachie-Adjei and Bullough found a 28% prevalence of DISH in subjects with an average age of 65 years. Lateral chest x-rays were reviewed in a study of African blacks with a prevalence of 3.9% increasing with age from 1% in those aged 40 to 49 years to 13.6% in individuals older than 70 years. In a similar study at the University of Minnesota, radiographs of consecutive patients found DISH in 25% of males over 50 years old and 15% of females over 50 years. Prevalence increased to 28% and 26%, respectively, over the age of 80 years. The patient population varied significantly from the aforementioned study, and the prevalence in African Americans, Native-Americans, and Asian populations was noted to be less than the total prevalence reported. A similar population-based study in Finland demonstrated DISH in 3.8% of men and 2.6% of women, with a subgroup analysis of Eastern Finland demonstrating higher rates with 10.1% in men older than 70 years. Though the etiology of DISH remains unclear to date, this evidence certainly indicates a genetic or at least regional factor as well as a higher prevalence in men that increases with age.

With regard to presentation, DISH is often an incidental finding noted on a chest x-ray or other radiograph obtained for an unrelated indication. However, patients do occasionally present with mild mid- or low-back pain or, more likely, back stiffness. Other extraspinal symptoms such as generalized joint stiffness or tendonitis may also be present, with Achilles tendonitis being particularly common.

Cervical Spine

DISH occurs occasionally in the cervical spine with preference for the lower cervical segments. The presence of DISH in the cervical spine primarily presents with midline pain and neck stiffness. Tolerance for large, anterior osteophytes in the cervical spine is significantly lower than in the thoracic or lumbar spine. Occasionally, dysphagia secondary to cervical osteophytes may be present in severe cases. In addition, impingement on other anterior neck structures including the trachea is possible. With this, patients may present with hoarseness or possibly difficulty with intubation. Impingement on the trachea by osteophytes is occasionally the primary culprit in sleep apnea. Other reports have been made of patients presenting with myelopathic symptoms secondary to focal outgrowth of fibrous tissue with severe stenosis.

There are few indications for surgical management specifically for DISH and no other potential pain generators. However, surgery may be appropriate in the setting of severe dysphagia or airway dysfunction. Impinging anterior cervical osteophytes may be excised either through an anterior paravertebral approach or via a transoral approach. Surgical excision should only be considered after other potential non-spine-related etiologies of dysphagia are ruled out, often through consultation with otolaryngologists.

Thoracic and Lumbar Spine

The presence of DISH in the thoracic spine is particularly common, and suspicion should remain high in patients with midaxial pain. Radiographs of the thoracic spine often reveal the aforementioned flowing osteophytes, particularly on the right anterolateral side. This differs from the cervical and lumbar spine, which has symmetric osteophyte formation. It has been postulated that the pulsatile action of the descending aorta has a protective effect on the left side of the spine, preventing the formation of osteophytes. This unilateral osteophyte formation may again cause pain and stiffness throughout the thoracic region. In addition, thoracic myelopathy has been reported secondary to DISH.

Laboratory values have not proven useful in the diagnosis of DISH but may be useful in ruling out other concerning diagnoses. These include typical infectious labs such as tests of complete blood count, erythrocyte sedimentation rate, and C-reactive protein. Osteoporosis labs may also prove useful in explaining axial back pain, including tests of calcium, vitamin D, parathyroid hormone, and others depending on specific protocol. A rheumatologic workup may be appropriate if radiographs are not entirely consistent with DISH.

Radiographs are the lone diagnostic tool for DISH and should include the region of complaint, frequently the thoracic or lumbar spine. Additional films may help to eliminate other potential etiologies. These may include two views of the cervical spine as well as the sacroiliac joint. However, if DISH is suspected, a chest radiograph or two views of the thoracic spine is diagnostic.

The flowing candlewax pattern of syndesmophytes differs significantly from the bamboo spine appearance of ankylosing spondylitis and should be easily differentiated on anteroposterior and lateral radiographs. The syndesmophytes are exclusively extra-articular and located along the anterior longitudinal ligament. Radiographic evaluation of patients with DISH presents special circumstances in the setting of trauma, and this particular issue is discussed later.

Treatment for back pain secondary to DISH in the cervical, thoracic, or lumbar spine frequently includes a combination of physical therapy, nonsteroidal anti-inflammatory drugs (NSAIDs), temporary bracing, and muscle relaxants. Of course, treatment for specific pain generators is important to consider, including epidural, foraminal, and facet injections. Conservative treatment is important in the setting of DISH and may be sufficient to alleviate pain.

Newer medications aimed at treatment of hyperostosis are under development, but none to date are available nor have they demonstrated effectiveness. Successful treatment with nontraditional therapies, including acupuncture and chiropractic manipulation, has been noted in single case reports.

Management of spinal pain secondary to DISH remains a significant challenge. Patients with DISH are vulnerable to common pain generators, including central spinal stenosis, foraminal stenosis, fractures and soft tissue injury, and deformity. Management of these disorders is beyond the scope of this chapter.