I don't have any personal experience with this but having looked through the guidance provided by the CAA I've come across the following:
- For a single episode of viral encephalitis with a seizure during the acute phase, Class 1 OML possible after 3 years, unrestricted never possible.
- The neurology guidance on centrally acting medicine suggests that in the case of anti-epileptics they are not compatible with medical certification (due to the underlying implication of epilepsy??).
My guess would be that they will likely require you to be off Keppra (unsure of withdrawal times they might require) and that you'll likely need an EEG to rule out any evidence of epileptiform activity. I imagine that they will want all of this performed under the guidance of a Consultant Neurologist (obviously don't just wean yourself off Keppra without the guidance of a medical professional).
I'm not sure that there is a thoroughly established pathway for this particular circumstance but my suggestion would be to get in touch with the AME you intend to use to renew your Class 1 (leading up to the 3 year minimum waiting period). Explain your circumstances, make sure that you have the necessary medical records from your clinic/hospital appointments from your initial illness and take it from there. Your AME should be able to guide you through the steps that will be necessary to regain your certificate in conjunction with the CAA and a Neurology Consultant.
Best of luck with the process.