The Neurosurgical Treatment of Movement Disorders

The management of movement disorders has been historically treated with both surgical and medical modalities. While L-Dopa has been the medical mainstay for Parkinson’s Disease, surgical techniques have evolved over the past century to the current state of stereotactic procedures in focal parts of the central nervous system. Presented here is a review of the history of this evolution. Over the past century, the approach of the medical institution to the treatment of movement disorders has evolved from neurosurgery to medical therapy and back to a combination of both, with significant improvement in each domain. Specifically, the current use of neurosurgery for the treatment of movement disorders has been greatly enhanced by the precision of stereotactic procedures. However, before the advent of stereotactic technology, neurosurgery for movement disorders progressed through various stages of experimentation with different methods and sites. An overview of that evolution is presented here. The earliest attempts to operate on the central nervous system (CNS) were aimed at the pyramidal system on the belief that the neural mechanisms responsible for normal movement must be responsible for the abnormal movements characterized by chorea, athetosis, hemiballismus, and parkinsonian tremor. Since then, the neurosurgical treatment of movement disorders within the central CNS has developed in both rationale and location, ranging from targeting the entire motor system to the current use of precise stereotactic procedures aimed at focal CNS components, particularly the basal ganglia, thalamus, and subthalamic nucleus (STN). The primary motor cortex, located in the precentral gyrus, was the first target of a neurosurgical approach to movement disorders. In 1890, Horsley reported that he had excised the corresponding portion of motor cortex in an attempt to treat athetosis, resulting in cessation of abnormal movement for two weeks (Horsley, 1890). In 1910, he also reported excising Brodmann’s Area 6 of the right premotor cortex with relief of symptoms for 14 months. However, the patient suffered a significant loss of sensory and motor function, only regaining partial voluntary movement after three weeks (Horsley, 1909). Similar results were achieved over the next few years with varying side effects (Gabriel and Nashold, 1998). Over the next 20 years, several other CNS and extra-CNS sites were targeted to relieve movement disorders, frequently with irreproducible results and limited publication. These included posterior rhizotomies (ablation of the spinal or cranial nerve root), sympathetic ramisection and/or sympathetic ganglionectomy, dorsal cordotomy, thyroidectomy, and cerebellar dentatectomy (Gabriel and Nashold, 1998). Some of these sites would be revisited by neurosurgeons years later, but for the most part the results were not outstanding. Despite the possible side effects of transient or permanent hemiparesis and/or hemianesthesia, the excision of the corresponding contralateral motor or premotor cortex was the standard approach for the next 20 years, with variations on the method of cortical ablation, including the induction of necrosis with ethanol injection (Nafzigger, 1937). However, the unacceptable side effects of cortical procedures, including paresis, aphasia, and seizures, prompted surgeons to explore distal sites in the pyramidal system such as the spinal cord, basal ganglia, and brainstem. In 1931, Putnam attempted to intervene at the spinal cord level. He first performed an anterolateral cordotomy for the treatment of athetosis, excising the anterior section of the cervical spinal cord medial to the dentate ligament. All five patients experienced diminished athetosis with the only adverse events being a mild motor deficit and hemianalgesia (Putnam, 1933). In a larger sample, 17 of 23 patients experienced improvement of athetosis for up to 5 years, but adverse effects included transient flaccid paralysis, transient incontinence, hemianesthesia, decreased male sexual function, and respiratory complications that led to death in three patients (Putnam, 1938, 1940). Parkinsonian tremor, however, was not relieved by anterolateral cordotomy. To focus on this problem, Putnam shifted his method to a lateral pyramidotomy; 20 of 22 patients reported initial relief and one-third reported long-term relief (Putnam, 1940, 1950). This approach was extended by Ebin in 1949 to a combined lateral and ventral pyramidotomy; all nine patients operated on experienced a reduction of tremor at rest for up to 20 months, with consequential motor strength reduction, loss of contralateral pain and temperature sensation, and transient urinary dysfunction