Neurosurgical considerations in osteopetrosis

Osteopetrosis is a metabolic bone disease resulting in skeletal hyper-sclerosis. Three major genetic subtypes of the disease are phenotypically expressed into three distinguishable forms of the disease, each dictating specific management. Autosomal recessive “severe” osteopetrosis occurs secondary to defective osteoclastic resorption of immature bone. Regarding the neurosurgical considerations in this group cranial concerns rather than spinal symptoms often predominate. Visual deterioration is the most frequent presenting complaint often beginning within the first few months of life. A secondary complication is hearing loss which is estimated to affect op to 78% of children within their first year of life. Here neurosurgical interventions for foraminal bony encroachment is of little long-term benefit with a more favourable outcome is seen with medical therapies. The autosomal recessive “intermediate form” of osteopetrosis is frequently not evident at birth and has a milder more protracted clinical course with individuals often surviving into adulthood. Labelled marble brain disease several case reports note the association between this form of the disease and intracranial calcifications and subsequent neuronal degeneration. Neurosurgical interventions have a beneficial role here but must be exercised in a patient specific manner. Autosomal dominant “benign” osteopetrosis has a relatively late onset typically occurring in early adolescence. In these individuals cranial nerve compression neuropathies are far less common with an approximate incidence of only 5%. These patients largely come to the attention of the attending neurosurgeon for the management of spinal complications which include spinal fractures, kyphoscoliosis, accelerated spinal degeneration and spinal osteomyelitis. Regarding the treatment of spinal fractures in patients with osteopetrosis no clear evidence-based guidelines currently exist. Several case reports note a high complication rate with surgical intervention however acceptable long term outcomes do occur with augmented, relatively protracted, post-operative bracing.