T–U

tardive dyskinesia See DYSKINESIA.

thalamotomy A surgical procedure in which the
neurosurgeon destroys a small portion of the THAL-
AMUS, which plays a role in certain kinds of motor
movement. Thalamotomy may be an appropriate
treatment for tremor-predominant PARKINSON’S
DISEASE, tremor disorders such as benign essential
tremor, and DYSTONIA. Neurosurgeons first per-
formed thalamotomy in the 1950s. Until recent
advances in technology, however, the risks of the
surgery (especially damage to adjacent BRAINstruc-
tures) were far greater than the benefits. Current
neurosurgery techniques use MAGNETIC RESONANCE
IMAGING(MRI) to locate the portions of the thala-
mus that participate in movement, typically the
ventral intermediate (VIM) nucleus. The neuro-
surgeon then uses MRI to precisely guide the
insertion and placement of a thin probe into the
VIM. A burst of heat through the electrode
ablates, or destroys, a few cells at a time until the
OPERATIONachieves the desired result. The person
remains conscious during the operation and
responds with movements as the neurosurgeon
directs.
The first step of thalamotomy is the placement
of a stereotactic halo, a circular brace the neuro-
surgeon attaches to the skull (done under local
anesthetic). The halo holds the instruments steady
and in precise position during the operation. The
neurosurgeon uses a local anesthetic to numb the
SKINand periosteum covering the cranium, the
only areas that contain nerves sensitive to PAIN,
and drills a small hole in the BONE. The neurosur-
geon slowly feeds the probe toward the thalamus,
using MRI to guide the process. The operation
takes 60 to 90 minutes, and improvement is
apparent immediately. The neurosurgeon removes

the stereotactic halo when the operation is com-

pleted. Complications are rare; when they do

occur they may include excessive bleeding, post-

operative INFECTION, and stimulation of taste or

visual disturbances (due to the probe passing near

or through these areas of the brain). Most people

return to full and regular activities in about two

weeks.

The effects of thalamotomy are permanent and

may end symptoms for some people, especially

those who have benign essential tremor. Symp-

toms often reemerge when the underlying condi-

tion is progressive. However, thalamotomy is not

very effective treatment for the DYSKINESIAof clas-

sic Parkinson’s disease.

See also DEEP BRAIN STIMULATION; PALLIDOTOMY;

SURGERY BENEFIT AND RISK ASSESSMENT.

tic An involuntary MUSCLE SPASMthat typically

occurs repetitiously and spontaneously. Tics most

commonly involve muscle groups in the face and

neck and may appear purposeful, such as an eye-

lid tic that gives the appearance of winking or a tic

involving the muscles around the MOUTH that

causes a person to look as though he or she were

grimacing. Vocal tics are spasms that involve the

VOCAL CORDSand produce noises such as grunts.

Tics are very common, especially in childhood,

and in isolation usually have no neurologic signifi-

cance. Some people experience tics during times

of anxiety. Tics that persist or occur in conjunction

with other symptoms may indicate a compressed

NERVEor an underlying neurologic or neuromus-

cular condition. Tic disorders that reflect neuro-

logic disturbances include TOURETTE’S SYNDROME

and tic douloureux (more commonly called

trigeminal NEURALGIA).

See also CEREBRAL PALSY; DYSKINESIA.

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