While most people with a reduced sense of smell will not develop Parkinson's, the majority of Parkinson's disease patients do have reduced sense of smell. Loss of sense of smell is often overlooked by diagnosing physicians as an early sign of PD. There are of course many other reasons a person may be experiencing a loss in sense of smell.
If you believe that you may have trouble with smell, consult your doctor.
Little is confirmed about what causes the early, pre-motor symptoms of Parkinson's, such as hyposmia, this loss of smell. But one prevalent theory in Parkinson's research about disease progression has to do with the protein alpha-synuclein, whose clumping is found in all people with the disease.
This theory, based on the research of Heiko Braak, MD suggests that the disease may start not in the substantia nigra (the region of the brain where loss of nerve cells leads to the dopamine deficit experienced by people with PD) but in the gastrointestinal system and the olfactory bulb, the part of the brain that controls sense of smell. Researchers have hypothesized that the alpha-synuclein clumps found in all people with Parkinson's may form in these parts of the body first, before migrating to other parts of the brain. Should this turn out to be true, and if researchers can find the clumps and break them up before they reach the brain, it may become possible to treat Parkinson's before major neurological damage occurs.
Early detection is a crucial step to understanding the causes of and developing better treatments for Parkinson's disease. Even before the typical tremor and slowness of movements occur in PD, it may be possible to detect early changes in the brain and symptoms that are associated with PD. Loss of sense of smell is a common but little noticed symptom that may occur years before the onset of motor symptoms or a PD diagnosis. That's why the Foundation's flagship study PPMI is studying a cohort of people with hyposmia to help determine the underlying connection and how it may improve diagnostics and potentially new treatments for PD.