Dogs have an extraordinary sense of smell and disease sniffing dogs have been studied as a diagnostic tool for a variety of conditions from diabetes to cancer. A new study suggests that dogs may be able to detect Parkinson disease before the clinical onset of symptoms, raising the elusive possibility of early intervention.
Parkinson disease is a progressive neurodegenerative disorder primarily characterized by motor symptoms including bradykinesia, resting tremor, and rigidity. Diagnosis is based on clinical findings, meaning that the disease process has already progressed before patients receive a formal diagnosis and begin therapy. The search for biomarkers for Parkinson disease is an active field of investigation because it could allow for early detection and management. Despite the identification of promising biomarkers, none have been specific enough to definitively diagnose Parkinson disease.
One early non-motor symptom in about half of patients with Parkinson disease is seborrheic dermatitis. While the cause of seborrheic dermatitis is not clear, accumulation of sebum (an oily, waxy substance secreted by sebaceous glands in the skin) has been observed in patients with Parkinson disease and could theoretically be an early biomarker of disease. Additionally, sebum has a distinctive odor, which makes it an attractive target for disease sniffing dogs.
In a recent study published in the Journal of Parkinson's Disease, two dogs were trained to distinguish between skin swabs collected from patients with Parkinson disease and healthy controls. After many weeks of training, the dogs were tested in a double-blind trial of 60 control and 40 test (Parkinson disease) skin swabs. Both the dog handler and experimenter were blinded, though we suppose the study could be considered triple-blinded since the dogs were unaware of which samples were which too. Amazingly, the two dogs detected Parkinson disease with sensitivities of 70 percent and 80 percent and specificities of 90 percent and 98 percent. In laymen’s terms, the dogs accurately detected Parkinson disease in 70-80 percent of test skin swabs and ignored 90-98 percent of the control swabs.
Another recent study evaluated the volatile components of sebum via mass spectrometry in patients with and without Parkinson disease to better understand the make-up of sebum in Parkinson disease. The researchers found a signature of volatile metabolites associated with Parkinson disease, which could provide another early sebum-related diagnostic method for Parkinson disease.
Since skin swabs are easy to collect and store, analysis of sebum could provide a novel non-invasive screening tool for Parkinson disease. Combined with other early non-motor symptoms and biomarkers, we could be one step closer to early detection and initiation of physical and medical therapy for patients with Parkinson disease before motor symptoms develop.
