Q: Initially my friend’s doctor thought he might have Parkinson’s, but now they say he has CBGD. What is this?

A: Cortical basal ganglionic degeneration is a rare degenerative brain condition first identified as a specific disease entity in 1967. It affects less than 1 per 100,000 people; it is thought to be sporadic, meaning it may occur in anyone, but it is possible there is a familial component in some cases. The cause of this condition is unknown, but it falls into the class of diseases where certain brain proteins (for CBGD it is the tau protein) develop abnormally (for CBGD the protein "folds" incorrectly).

As with Parkinson’s disease, patients with CBGD usually present with movement abnormalities, hence CBGD is sometimes referred to as an "atypical" Parkinson-like disease. About 5 percent of patients evaluated in specialized movement disorder clinics are subsequently diagnosed with CBGD. However, while Parkinson's patients typically have motor symptoms that include slow movements called bradykinesia, rigid movements, resting tremor and/or gait abnormalities that affect both sides of the body, the motor symptoms of CBGD patients typically present asymmetrically, usually beginning in one limb.

The symptoms in CBGD patients usually begin insidiously between the ages of 50 and 70, and progress over several years (patients usually survive 2 to 12 years, average about 7, after the clinical diagnosis is made). The symptoms include progressive loss of motor function (explaining why pneumonia, caused by the loss of breathing muscle function, is the most common acute complication leading to death in CGDB patients) which typically starts in one limb and eventually compromises the patient’s ability to walk, progressive dementia, "alien" limb syndrome (where the patient may say their limb seems to move "with a mind of its own"), cognitive impairment, as well as other symptoms (which may include hallucinations, sensory loss, rigidity, speech alterations, compromise of the muscles that move the eyes, and many others). CBGD patients do not typically develop a resting tremor (as do PD patients), and there are other characteristics (such as no loss of autonomic functions) that help differentiate it from other conditions.

There is no definitive test for CBGD; the diagnosis is based on the clinical symptoms and by excluding other conditions (for example ruling out a stroke in a patient who has weakness of a single limb). Therefore, the tests done when CBGD is suspected (certain blood tests and imaging tests, such as a brain MRI) are to help rule out other conditions. For example, “probable CBGD” is diagnosed in patients with an asymmetric motor limb presentation who have two of the following symptoms: limb rigidity or akinesia; limb dystonia; or limb myoclonia, in addition to two of the following additional symptoms: limb apraxia; cortical sensory deficit; or alien limb phenomena. Since CBGD is a clinical diagnosis, verification of the diagnosis may require evaluation of the patient’s brain at autopsy.

Currently there is no specific treatment for CBGD patients. Certain medications used for Parkinson's disease may help alleviate some of the symptoms, and other supportive care is indicated. Due to the progressive nature of this disease, both the patient and their family should be included in health care plan discussions.

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.