Diffuse idiopathic skeletal hyperostosis

What is diffuse idiopathic skeletal hyperostosis (DISH)?

Diffuse idiopathic skeletal hyperostosis (DISH) is a disease of the ligamentous structures of the spine. The cause of DISH is unknown. The hallmark of this disease is confluent ossification of the spinal ligamentous structures that spans at least three spinal interspaces. DISH occurs most commonly in the thoracolumbar spine, but it also can affect the cervical spine, ribs, and bones of the pelvis.

DISH has also been called Forestier’s disease and ankylosing hyperostosis. It is a bone-forming condition in which ossification occurs at skeletal sites subjected to stress. It occurs most frequently in the thoracic spine, leading to stiffness or decreased motion.

Pain is usually not a significant symptom; if severe, the patient should be evaluated for other causes of pain. Involvement of the cervical spine can cause dysphagia. DISH occurs in approximately 12% of the elderly population and may coexist with other disorders, particularly type 2 diabetes mellitus.

Causes of Abnormal Bone Growth in and About the Axial Skeleton

Seronegative spondyloarthropathies
Acromegaly
Charcot neuroarthropathy
Trauma
Degenerative changes
Diffuse idiopathic skeletal hyperostosis
Abnormal urate deposition
Excessive fluoride intake
Ochronosis

Also known as Forestier disease , DISH causes stiffness and pain of the cervical and thoracolumbar spine. The symptoms are worse on wakening and at night. When the disease affects the cervical spine, cervical myelopathy may result. If anterior spurring of the cervical spine occurs, dysphagia may result. DISH is a disease of the late fifth and early sixth decades. It also can cause a relative spinal stenosis with intermittent claudication. It affects men twice as commonly as women. DISH is a disease that affects primarily whites. Patients with DISH have a higher incidence of diabetes mellitus, hypertension, and obesity than the general population. DISH usually is diagnosed by plain radiographs of the spine.

What are the Symptoms of Diffuse idiopathic skeletal hyperostosis

A patient with DISH reports stiffness and pain in the area of the affected spinal segments or bone. Patients also may note numbness, weakness, and lack of coordination in the extremities subserved by the spinal segments affected by DISH. Muscle spasms, back pain, and pain referred to the buttocks are common. Occasionally, a patient with DISH experiences compression of the spinal cord, nerve roots, and cauda equina, resulting in myelopathy or cauda equina syndrome. DISH is the second most common cause of cervical myelopathy after cervical spondylosis. Patients with lumbar myelopathy or cauda equina syndrome experience varying degrees of lower extremity weakness and bowel and bladder symptoms; this represents a neurosurgical emergency and should be treated as such.

How is Diffuse idiopathic skeletal hyperostosis diagnosed?

Radiographic findings in DISH

DISH is diagnosed by plain radiographs. Confluent ossification of the spinal ligamentous structures spanning at least three interspaces is pathognomonic for the disease. Disk space height is preserved and sacroiliac joints are spared in patients with DISH. If myelopathy is suspected, magnetic resonance imaging (MRI) of the spine provides the best information regarding the status of the spinal cord and nerve roots. MRI is highly accurate and helps identify other abnormalities that may put the patient at risk for the development of permanent spinal cord injury.

In patients who cannot undergo MRI, such as a patient with a pacemaker, computed tomography (CT) or myelography is a reasonable second choice. Radionucleotide bone scanning and plain radiographs are indicated if fracture or bony abnormality, such as metastatic disease, is being considered.

Normal bone mineralization is seen in addition to “flowing” ossification of the anterior longitudinal ligament connecting at least four contiguous vertebral bodies.

The calcification of the anterior longitudinal ligament is seen as a radiodense band separated from the anterior aspect of the vertebral bodies by a thin radiolucent line, similar to flowing candle wax. Ossification of multiple tendinous or ligamentous sites in the appendicular skeleton may also be seen. Disc spaces, apophyseal joints, and sacroiliac joints are typically normal on radiographs, helping to separate DISH from OA and ankylosing spondylitis.

Although this testing provides useful neuroanatomical information, electromyography and nerve conduction velocity testing provide neurophysiological information that can delineate the actual status of each individual nerve root and the lumbar plexus. Screening laboratory tests, consisting of complete blood cell count, erythrocyte sedimentation rate, and automated blood chemistry testing, should be performed if the diagnosis of DISH is in question.

Differential Diagnosis

DISH is a radiographic diagnosis that is supported by a combination of clinical history, physical examination, and MRI. Pain syndromes that may mimic DISH include neck and low back strain; bursitis; fibromyositis; inflammatory arthritis; ankylosing spondylitis; and disorders of the spinal cord, roots, plexus, and nerves. Thirty percent of patients with multiple myeloma or Paget disease also have DISH. Screening laboratory tests consisting of complete blood cell count, erythrocyte sedimentation rate, antinuclear antibody testing, human leukocyte antigen (HLA) B-27 antigen screening, and automated blood chemistry testing should be performed if the diagnosis of DISH is in question to help rule out other causes of the patient’s pain.

Treatment

DISH is best treated with a multimodality approach. Physical therapy, including heat modalities, range-of-motion exercises, and deep sedative massage, combined with nonsteroidal antiinflammatory drugs (NSAIDs) and skeletal muscle relaxants represents a reasonable starting point. The addition of steroid epidural nerve blocks is a reasonable next step if pain remains a problem. Underlying sleep disturbance and depression are best treated with a tricyclic antidepressant compound, such as nortriptyline, which can be started as a single bedtime dose of 25 mg.

Complications and Pitfalls

Failure to diagnose DISH accurately may put the patient at risk for the development of myelopathy, which, if untreated, may progress to paraparesis or paraplegia. Electromyography helps distinguish plexopathy from radiculopathy and helps identify coexistent entrapment neuropathy, which may confuse the diagnosis.

Clinical Pearls

Given the association of DISH with multiple myeloma and Paget disease, these potentially life-threatening diseases must always be included in the differential diagnosis. DISH and degenerative arthritis and discogenic disease may coexist. Each disease process may require its own specific course of treatment.

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