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Published on: September 3, 2020
Scotopic threshold response changes after vigabatrin therapy in a child without visual field defects: a new
Pasquale Parisi1, Paolo Tommasini, Giuseppe Piazza
1Child Neurology, Department of Pediatrics, La Sapienza 2 University, c/o Sant'Andrea Hospital, Via di Grottarossa, 1035-1039 Rome, Italy. parpas@iol.it
Insights
Vigabatrin (VGB) therapy can alter the scotopic threshold response (STR), an electroretinogram (ERG) marker, in patients with epilepsy. This finding may help identify early retinal damage from GABA-ergic drugs.
Area of Science:
- Ophthalmology
- Neuroscience
- Pharmacology
Background:
- Vigabatrin (VGB) is used for drug-resistant epilepsy and West syndrome.
- Visual field loss has been reported with VGB therapy.
- Electrophysiologic markers are sought to understand VGB-induced retinal damage.
Observation:
- A 13-year-old male patient received VGB monotherapy.
- Complete electroretinography (ERG) was performed before and after VGB initiation.
- Only the scotopic threshold response (STR) showed alterations.
Findings:
- The STR, a specific ERG wave, was reduced after VGB therapy.
- The STR is mediated by glial K+ spatial buffer currents.
- This is the first report linking VGB to STR reduction.
Implications:
- The study suggests VGB may affect retinal glia.
- STR changes could serve as an early marker for VGB retinal toxicity.
- This ERG response may aid in evaluating new GABA-targeting drugs.
Abstract:
Vigabatrin (VGB) has been widely used in patients affected by drug-resistant epilepsy and West syndrome. Following reports of visual field loss associated with vigabatrin therapy, some authors have investigated retinal electrophysiologic variables to identify early electrophysiologic markers and pathogenetic mechanisms of retinal damage. There are no previous reports of a scotopic threshold response (STR) reduction associated with vigabatrin therapy. A 13-year-old male child was submitted to a complete electroretinographic study before and after the start of vigabatrin therapy. Of the electroretinographic responses analyzed, only the scotopic threshold response was altered. The scotopic threshold response is a corneal-negative wave in the electroretinogram (ERG) of a fully dark-adapted eye. In cat, this response has been shown to be mediated by K+ spatial buffer currents that flow from proximal to distal retina in retinal glia as a result of elevated concentration of K+ in proximal retina following depolarization of local neurons in response to light onset. The prospective nature of the study in a previously untreated patient on vigabatrin monotherapy allows us to speculate on the underlying pathogenetic mechanisms and level of action of vigabatrin therapy-related retinal damage. If the predictive value of the scotopic threshold response changes is documented, this ERG response could be used to perform a preliminary evaluation of drugs, which modify gamma-aminobutyric acid (GABA) receptors and/or GABA levels.
