Spinal manifestations of Paget's disease

Principles of management of osteometabolic disorders affecting the aging spine

Osteoporosis is the most common contributing factor of spinal fractures, which characteristically are not generally known to produce spinal cord compression symptoms. Recently, an increasing number of medical reports have implicated osteoporotic fractures as a cause of serious neurological deficit and painful disabling spinal deformities. This has been corroborated by the present authors as well. These complications are only amenable to surgical management, requiring instrumentation. Instrumenting an osteoporotic spine, although a challenging task, can be accomplished if certain guidelines for surgical techniques are respected. Neurological deficits respond equally well to an anterior or posterior decompression, provided this is coupled with multisegmental fixation of the construct. With the steady increase in the elderly population, it is anticipated that the spine surgeon will face serious complications of osteoporotic spines more frequently. With regard to surgery, however, excellent correction of deformities can be achieved, by combining anterior and posterior approaches. Paget's disease of bone (PD) is a non-hormonal osteometabolic disorder and the spine is the second most commonly affected site. About one-third of patients with spinal involvement exhibit symptoms of clinical stenosis. In only 12-24% of patients with PD of the spine is back pain attributed solely to PD, while in the majority of patients, back pain is either arthritic in nature or a combination of a pagetic process and coexisting arthritis. In this context, one must be certain before attributing low back pain to PD exclusively, and antipagetic medical treatment alone may be ineffective. Neural element dysfunction may be attributed to compressive myelopathy by pagetic bone overgrowth, pagetic intraspinal soft tissue overgrowth, ossification of epidural fat, platybasia, spontaneous bleeding, sarcomatous degeneration and vertebral fracture or subluxation. Neural dysfunction can also result from spinal ischemia when blood is diverted by the so-called "arterial steal syndrome". Because the effectiveness of pharmacologic treatment for pagetic spinal stenosis has been clearly demonstrated, surgical decompression should only be instituted after failure of antipagetic medical treatment. Surgery is indicated as a primary treatment when neural compression is secondary to pathologic fractures, dislocations, spontaneous epidural hematoma, syringomyelia, platybasia, or sarcomatous transformation. Five classes of drugs are available for the treatment of PD. Bisphosphonates are the most popular antipagetic drug and several forms have been investigated.

The neurologic complications of Paget's disease

Paget's disease of bone is associated with involvement of the central and peripheral nervous system. The brain, spinal cord, cauda equina, spinal roots, and cranial nerves can be affected in Paget's disease due to their anatomic relationship to bone. Neurologic syndromes are uncommon but include headache, dementia, brain stem and cerebellar dysfunction, cranial neuropathies, myelopathy, cauda equina syndrome, and radiculopathies. The central complications result from pagetic involvement of the skull. Expansion of diseased bone can result in compression of cranial nerves as they exit their bony foramina. Softening of the skull leads to basilar invagination with compression of the brain stem, cerebellum, and lower cranial nerves. Brain stem compression can cause hydrocephalus. Rarely, there is direct compression of the brain from acute epidural hematoma or hypertrophy of the calvarium. Myelopathy, cauda equina syndrome, and radiculopathies most commonly result from hypertrophy of the spine with direct compression. Spinal stenosis can also result from ossification of extradural structures or pathologic fractures. Ischemia from vascular compression or a steal syndrome has also been described. Neurologic complications rarely occur due to sarcomatous transformation of pagetic bone. Magnetic resonance imaging (MRI), computerized tomography (CT)-myelography, and bone X-rays are helpful to localize the lesion and direct therapy. Treatment options include surgical decompression, ventricular shunt placement, and medical management with calcitonin and/or the bisphosphonates. The selection of treatment will vary depending upon the rate of progression and the severity of the neurologic deficit.