easily remedied causes for the symptoms. Among
such causes might be undiagnosed conditions such
as HYPOTHYROIDISM, DIABETES, vitamin B 12 defi-
ciency, neurosyphilis, and medication reactions or
interactions. The doctor will also take a careful
medical history, looking for evidence of recent
injury or trauma or of family history of conditions
such as Parkinson’s disease and Alzheimer disease.
The doctor may conduct diagnostic imaging proce-
dures such as MAGNETIC RESONANCE IMAGING(MRI)
andCOMPUTED TOMOGRAPHY(CT) SCANto rule out
BRAIN TUMOR, brain hemorrhage, or stroke.
Dementia is generally a clinical diagnosis based on
symptoms and on ruling out treatable causes of
the symptoms.
Treatment Options and Outlook
Treatment and outlook vary with the cause of the
dementia. Metabolic dementia is often transient,
with normal brain function returning when treat-
ment restores the body’s metabolic balance.
Dementia that results from injury to the brain or
neurodegenerative conditions such as Alzheimer’s
disease is generally permanent. Treatment aims to
improve remaining cognitive abilities through
activities that use and exercise the brain, such as
reading and crossword puzzles. Adaptive measures
may also help, such as writing out instructions or
drawing maps or pictures. Persistent, and particu-
larly progressive, dementia may result in loss of
independent function.
Risk Factors and Preventive Measures
Age is the primary risk factor for dementia. About
half of people over age 85 have Alzheimer’s dis-
ease, the leading cause of dementia. Lewy body
dementia and vascular dementia also become sig-
nificantly more common with advanced age.
Appropriate medical and lifestyle management of
conditions such as HYPERTENSION(high BLOOD PRES-
SURE), atherosclerosis, LIVERdisease, and diabetes
helps mitigate their health consequences.
See also COGNITIVE FUNCTION AND DYSFUNCTION;
CREUTZFELDT-JAKOB DISEASE; DELIRIUM; MEMORY AND
MEMORY IMPAIRMENT.
dermatome A region of the body a specific, sin-
gle spinal NERVEroot serves. The SPINAL NERVEScon-
vey motor signals to and sensory signals from the
body. The body’s dermatome pattern is fairly con-
sistent among individuals though each person has
subtle unique characteristics. Identifying the
involved dermatome for chronic PAIN, MUSCLE
weakness, or PARALYSIShelps the neurologist deter-
mine the region of the spine where the damage
originates. This is particularly useful for therapies
such as NEURAL BLOCKADE(NERVE BLOCK) and RHIZO-
TOMY, which are treatments for intractable pain or
spasticity. The body’s dermatome has the appear-
ance of a topographic map when rendered as a
visual representation.
A dermatome is also a bladed surgical instru-
ment used to remove very thin layers of SKINsuch
as for skin transplantation.
See also CEREBRAL PALSY; COMPLEX REGIONAL PAIN
SYNDROME; SPINAL CORD INJURY.dyskinesia Abnormal, involuntary movements.
Dyskinesia results from damage to the structures
within the BRAINresponsible for motor movement
and coordination, notably the basal ganglia.
ATHETOSIS, CHOREA, DYSTONIA, MYOCLONUS, tics, and
tremors are all forms of dyskinesia that may
appear in neurologic disorders such as PARKINSON’S
DISEASE, HUNTINGTON’S DISEASE, TOURETTE’SSYN-
DROME, RESTLESS LEGS SYNDROME, CEREBRAL PALSY, and
essential benign tremor. Abnormally slow move-
ments are bradykinetic (bradykinesia) and abnor-
mally rapid movements are hyperkinetic
(hyperkinesis). It is common for people who have
neuromotor disorders to have more than one form
of dyskinesia. Medications such as anticholinergics
and MUSCLE relaxants can sometimes improve
dyskinesia.
Tardive dyskinesia is a form of dyskinesia that
develops with long-term use of DOPAMINEantago-
nist medications, which block dopamine from
reaching dopamine receptors in the brain.
Dopamine antagonists are the convention of treat-
ment for Parkinson’s disease. Many ANTIPSYCHOTIC
MEDICATIONSto treat SCHIZOPHRENIAand other seri-
ous psychiatric illnesses also are dopamine antago-
nists. Tardive dyskinesia is often irreversible.
See also TREMOR DISORDERS.dyslexia See LEARNING DISORDERS.252 The Nervous System