Canine detection of volatile organic compounds unique to human epileptic seizure

Abstract

Objective: Literature accounts of service dogs alerting patients prior to their seizures are a mix of historically poor quality data and confounding diagnoses. In a group of epilepsy patients, Canine Assistants and Florida International University characterized a unique scent combination of volatile organic compounds present during the immediate postictal period, but never at other times. The current study was designed to confirm prospectively if this unique scent, and potential biomarker, can: (1) be detected in an epilepsy monitoring unit (EMU), (2) whether this scent is present with nonepileptic seizures, and (3) whether this scent also precedes the clinical-electrographic seizure.

Methods: Following consent and approval, sweat samples taken from EMU admissions at Denver Health Medical Center were sent to Canine Assistants in Georgia. Their team of service dogs, who had been imprinted to recognize the unique scent, were then asked to process these sweat samples in a simple yes/no identification paradigm.

Results: Sixty unique subjects were enrolled over a two-year period. In the first part of this study, a total of 298 ictal sweat samples of 680 total observations were collected. The dogs had a 93.7% (OR: 14.89, 95% CI: 9.27, 23.90) probability of correctly distinguishing between ictal and interictal sweat samples. In the nonepileptic seizure population, 18 of the 19 NES events that were accompanied by sweat sample collections were not associated with identification of the unique seizure scent. In the second part of the study, in which subjects had samples collected every hour, dogs identified the unique seizure scent presence before 78.7% of all seizures captured, at a probability of 82.2% (OR: 4.60, 95% CI: 0.98, 21.69) of a positive detection predicting a seizure. The average duration of the warning phase of the scent was 68.2 min. The average duration of the tail phase of the scent faded after 81 min.

Significance: This study confirms the unique seizure scent identified by Canine Assistants and FIU may be collected and recognized by dogs trained to do so, in a prospective manner. A significant number of seizures appear to be associated with the unique scent presence prior to clinical-electrical onset of the seizure itself, and therefore further study of this biomarker is warranted.

Keywords: Canine scent detection; Epilepsy biomarker; Epileptic seizure; Seizure alert dog; Seizure prediction; Volatile organic compounds (VOC).