Corticobasal degeneration (CBD) is a form of atypical parkinsonian
(parkinsonism plus) syndrome of unknown cause. As the name implies,
CBD results in gradual loss of nerve cells (neurodegeneration) in the
surface of the brain (cortex) and the deep structures (basal ganglia)
involved in control of movement. In contrast to other categories of
atypical parkinsonism, the neurodegeneration in CBD is markedly
asymmetrical and thus the symptoms usually start on one side of body
and remain asymmetrical throughout the course of the disease. The
most characteristic presenting feature of CBD is the gradual loss of
use of one hand or leg (called "apraxia"). Patients may also
experience abnormal postures of limbs or neck (dystonia), painful
rigidity, muscle spasms, and eventually irreversible muscle
contractures, all involving the same side of the body. They may have
a jerking movement (myoclonus) of one hand at rest and/or when using
the hand. Some patients also have difficulties with their speech and
language (primary progressive aphasia). Although some cognitive
changes may be noted early in the course of the disease, dementia
usually occurs only in more advanced stages. On examination, there is
often loss of sensation in one or both sides of the body. On
occasion, an affected limb can seem to have a "mind of its own", and
make seemingly purposeful movements that the patient cannot control
(known as "alien" hand or foot). The symptoms usually progress over 3-
8 years and eventually the patient develops gait and balance problems
and has difficulties with ambulation, becoming wheelchair bound and
bedridden.
Joseph Jankovic, M.D.
There is no diagnostic test for CBD, but the neurologist usually
suspects the diagnosis based on the clinical presentation of
asymmetrical, progressive symptoms and signs. Imaging studies are not
usually very helpful, but CT or MRI may show asymmetrical shrinkage
of cortical (brain surface) areas on the side opposite to the
affected limbs. In some cases the diagnosis cannot be confirmed until
an autopsy examination of the brain which usually shows the typical
findings of focal, asymmetrical neuronal degeneration in the cortex
and basal ganglia, as well as other deep brain structures.
Microscopic examination shows "ballooned" neurons and other
characteristic abnormalities.

As with the other atypical parkinsonian syndromes, treatment with
levodopa and related medications is only rarely, if ever, helpful.
Sometimes muscle spasms and jerking can be reduced with muscle
relaxants, such as clonazepam, and with botulinum toxin injections
into affected parts of the body.