"In such case" and "in such a case"

• In such a case
• In such case

The former is the most common of the two expressions and is widely used. In such case, however, is mostly restricted to formal writing. It is very common in law, medicine and the sciences. It wouldn't be a good idea to use this in other registers, for example in fiction or letters to friends.

The meaning of the two terms is very similar, but there's one difference that I can think of. This is that in such case can sometimes mean if this is the case as in if this is the case right now. So a lawyer for example might say:

• It has been suggested to us that you might have retained a copy of the keys for the premises. In such case, please return them immediately.

We can't really use in such a case in this instance, because in such a case can only really mean in cases like this one. It can't mean if this is the case.

Aside from this the two are basically freely interchangable in most of those registers where in such case occurs (I'll make a hedge here, in that I don't know if the legal use of the term has any special caveats).

In terms of grammar, there is also one important distinction which could account for the perseverance of in such case in formal writing. This is that in such case can take a content clause as a complement. In such a case does not. Here are a couple of examples:

• Even in such case that the user would have copied the Client Program, the use thereof would be impossible without the connection keys generated by the Connection Manager.

[MP Nieminen, K Kalpio, J Rinkinen - US Patent 6,578,075, 2003 ]

• In such case that the barrier to resistance of a number of molecules needs to be compared, resistance selection protocols need to be developed ... .

[I Vliegen, L Delang, J Neyts - Antiviral Methods and Protocols, 2013 ]

In these instances the idiom in such case is behaving like a conjunctive preposition (read 'subordinating conjunction').