Basket case

That's going to happen to me after this year, I swear. I will end up as a basket case in some looney bin institution. This week I have been learning about cases in Old Irish (gömlu góðu föllin í málfræði). In Gaelic there are four cases, not too bad, most of the time, but in Old Irish there is one extra. I was telling my friend about them; the nominative (nefnifall), genetive (eignarfall), dative or the prepositional (þágufall), vocative (ávarpsfall) and the last one acusative (þolfall). After this long list of cases my friend suggested that there was a case missing from all of this and I tend to agree with her. There is definitely one case missing - it's the abusive case. There really should be something like that in the list as well. Maybe there even once was since in the old Indo-European language there were 8 cases.
In Icelandic we have four, but we also have 3 genders, masculine, feminine and neuter. Not a problem there, and very easy to understand and figure out what belongs where, when you get your head around the definite article. We have the same cases as Old Irish except the vocative one, I think it is because we are not used to address anyone that we do not know in any other way than: "Hey you!" or "Listen" (Heyrðu) which sounds better and not too rude in Icelandic.