Is MS a Diagnosis of Exclusion? Part 1
One of the readers of this column asked me to write about whether MS is a disease of exclusion. Simply put, it is not. Let me explain what the phrase “a disease of exclusion” means by using Parkinson’s disease as an example. Parkinson’s disease is a movement disorder caused by the degeneration of cells that produce dopamine in a part of the brain called the substantia nigra. Like MS, no one knows its cause and, while there are powerful medications and neurosurgical procedures to control the symptoms, there is nothing to prevent the slow, but relentless progression of the disease.
Parkinson’s disease presents with a number of characteristic features. The major features include a resting tremor that usually starts on one side of the body, slowness of movement (bradykinesia), rigidity of the extremities, and postural instability. Other features include depression, loss of smell, a characteristic “shuffling” gait, decreased facial expression, small handwriting, and sleep disturbances. Only in the later stages of the illness are all features likely to be present. Like with MS, a thorough history and physical exam are the keys to diagnosis.
Also like MS, there are a number of conditions that can cause similar symptoms to Parkinson’s disease. Neurologists will make a distinction between Parkinson’s disease itself and those mimics that cause what is instead called Parkinsonism. These mimics include medications that block dopamine (such as antipsychotics or anti-nausea medications), structural disorders of the brain, essential tremor, multiple strokes, brain tumors, and a large number of other neurodegenerative disorders that are often called Parkinson’s plus syndromes.
Currently, there are no laboratory or imaging tests to diagnosis Parkinson’s disease that are in widespread use; though the use of single-photon emission computed tomography (SPECT) for detecting dopamine transporters can be useful to help confirm the diagnosis. Therefore, a diagnosis of Parkinson’s disease is made when a patient presents with the appropriate history, clinical symptoms, and when all other reasonable causes of these symptoms have been eliminated. For this reason, it is fair to say that Parkinson’s disease is a diagnosis of exclusion. In my next post, I will describe why this is not the case for MS.
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