or use (gasp) COALESCE 😉
select @searchvar = case when COALESCE(@var1,@var2,@var3) is null and @var4 is not null then 'RESULT' else '1' end
But we believe the OP is trying to use @var4 as a search string, and @var1,@var2,@var3 are used to tell the procedure which column to search on.
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Against stupidity the gods themselves contend in vain. -- Friedrich Schiller
Stop, children, what's that sound? Everybody look what's going down. -- Stephen Stills