Gastrointestinal barriers to levodopa transport and absorption in Parkinson's disease.

Levodopa is the gold standard for the symptomatic treatment of Parkinson's disease (PD). There are well documented motor and non-motor fluctuations, however, that occur almost inevitably once levodopa is started after a variable period in people with PD. Whilst brain neurodegenerative processes play a part in the pathogenesis of these fluctuations, a range of barriers across the gastrointestinal (GI) tract can alter levodopa pharmacokinetics, ultimately contributing to non-optimal levodopa response and symptoms fluctuations. GI barriers to levodopa transport and absorption include dysphagia, delayed gastric emptying, constipation, Helicobacter pylori infection, small intestinal bacterial overgrowth and gut dysbiosis. In addition, a protein-rich diet and concomitant medication intake can further alter levodopa pharmacokinetics. This can result in unpredictable or sub-optimal levodopa response, 'delayed on' or 'no on' phenomena. In this narrative review, we provided an overview on the plethora of GI obstacles to levodopa transport and absorption in PD and their implications on levodopa pharmacokinetics and development of motor fluctuations. In addition, management strategies to address GI dysfunction in PD are highlighted, including use of non-oral therapies to bypass the GI tract.

The operational definition of epileptiform discharges significantly improves diagnostic accuracy and inter-rater agreement of trainees in EEG reading.

To assess whether trainees can learn and implement the operational definition of interictal epileptiform discharges (IEDs) of the International Federation of Clinical Neurophysiology (IFCN), based on six morphological criteria, and whether its implementation improves their diagnostic performance and inter-rater agreement (IRA). Seven trainees evaluated a balanced dataset of 70 EEG samples containing sharp transients (35 from patients with epilepsy and 35 from patients with non-epileptic paroxysmal events). The gold standard was derived from video-EEG recordings of the habitual clinical episodes. The trainees individually reviewed the EEGs, blinded to all other data, in two successive training sessions, three months apart. The second session was preceded by a teaching module about the IFCN criteria, and the trainees implemented them during the second reading session. By implementing the IFCN criteria, trainees significantly improved their specificity (94.29% vs. 77.14%; p=0.01) and overall accuracy (81.43% vs. 64.29%; p=0.01) for identifying IEDs. Sensitivity also improved but did not reach the level of statistical significance (77.14% vs. 60%; p=0.07). IRA improved significantly from fair (k=0.31; 95% CI: 0.22-0.40) to high-moderate (k=0.56; 95% CI:0.46-0.67) beyond-chance agreement. Implementing the IFCN criteria significantly improves the diagnostic performance and IRA of trainees in identifying IEDs. Teaching the IFCN criteria for IEDs will increase specificity in clinical EEG and avoid over-reading, the most common cause of misdiagnosing epilepsy.