I have wierd nail problems too!!!
Ever since I got GBS I have been experiencing this thng I would call a double toenail on both my big toes. My neurologist has never in his career seen anything like this. As the nails look healthy but they as well split well up the nail bed in a horizontal position. Until lately there has always been a nail underneath but this time the nail underneath was way to thin and soft and came off with the second nail leaving a wonderful practically bare toe. It is heealing now slowly but this strange occurance I hope will end this time as the nail has to somehow grow straight without diveting downwards by the other nail being on top. My fingernails are very brittle and become malformed every now and then. My neurologist said to me it is common after nerve damage to have nail, skin and a whole host of problems afterwards.
Hope that helps.