Parkinson's disease is one of the most common neurological disorders to affect older people. In patients with Parkinson's, the nerve cells, or neurons, that produce the neurotransmitter called dopamine are destroyed, causing many different symptoms. Movement-related symptoms in Parkinson's include bradykinesia--an overall slowing of movement; tremor--an involuntary shaking, often in the hands; rigidity--resistance to someone else moving the patient's arm or leg; and postural instability--difficulty maintaining balance. When patients show movement abnormalities that look like those of Parkinson's disease, this is called parkinsonism. Several diseases or conditions can cause such symptoms.
Lewy Body Dementia
Lewy body dementia is a degenerative neurological disease that gets its name from the small clusters of intracellular proteins, called Lewy bodies, that are found around cortical neurons--the nerve cells within the brain that are involved in thinking, voluntary movement, and sensation. While it was once only rarely diagnosed, it is becoming recognized as a very common degenerative dementia, second only to Alzheimer's disease in its frequency. The National Institutes of Health website MedlinePlus explains that making the diagnosis of Lewy body dementia is often difficult because its symptoms overlap with both Parkinson's disease and Alzheimer's disease. As with Parkinson's disease, patients with Lewy body dementia often suffer from bradykinesia. A patient with bradykinesia may have an abnormal gait called a "shuffling gait"--rather than walking normally, he will seem to be shuffling slowly, with small steps. Rigidity is also a hallmark feature of the parkinsonism found in Lewy body dementia. Tremor, which is a cardinal feature in Parkinson's, is found in Lewy body dementia but is not as common. The overlap with Alzheimer's is the cognitive decline that is seen in patients with Lewy body dementia. However, according to Dr. Ann Marie Hake and Dr. Martin Farlow, writing in the medical reference UpToDate, visual hallucinations are more rarely seen in Alzheimer's disease but are very common in Lewy body dementia, occurring in approximately two-thirds of patients.
Medication-Induced Secondary Parkinsonism
Secondary parkinsonism is the term used to describe the entire group of disorders that causes Parkinson's like abnormalities. Such disorders can be due to brain-related diseases, such as meningitis or stroke. However, certain medications can cause damage to the cells within the brain that dopamine. If dopamine is not being produced normally, the symptoms that result will look very similar to those of Parkinson's disease, even though the patient does not actually have Parkinson's. MedlinePlus lists several medications that may cause secondary parkinsonism. These include antipsychotic medications such as haloperidol, which is used for treating schizophrenia as well as the motor tics associated with Tourette's disorder. Metoclopramide is used to treat a condition called diabetic gastroparesis, which is abnormally slow stomach emptying due to diabetes. It may also be used for treated gastric esophageal reflux disease. Unfortunately, it may also cause secondary parkinsonism. Finally, a group of medicines called phenothiazines--these are drugs used for treating the vomiting and nausea that often accompany chemotherapy--may cause secondary parkinsonism, because they block the receptors that dopamine usually binds to within the brain.
Progressive Supranuclear Palsy
Progressive supranuclear palsy, or PSP, is a rare type of dementia that initially can look very similar to Parkinson's disease. Patients with PSP have symptoms of gait abnormalities, just as patients with Parkinson's disease have. However, a feature that may help distinguish PSP from Parkinson's disease is that patients with PSP have certain eye-related changes. Specifically, a PSP patient may have trouble looking downward without moving his whole head--this is because the nerves that control these eye movements have been destroyed by the disease. Sadly, as with Parkinson's disease and Lewy body dementia, there is no cure for the disease; treatment focuses on improving symptoms as much as possible, but eventually the patient will die from the disease.