Update SQL Help Needed - SQL 2005 TSQL

Per my client, when it creates the qualifier for 'HCPS-DEN"' it needs to create the qualifier as 'AD' not 'HC'. Currently, with the present update script its inserting 'HC' on all. I need it to say when the 'HCPS-DEN' is used, insert the 'AD' not 'HC'. Everything else should be the HC.

I tried using a CASE statement:
CASE WHEN Description = 'HCPC - DEN' THEN 'AD' ELSE 'HC' END

however I get this back:

Msg 207, Level 16, State 1, Line 10
Invalid column name 'Description'.

I was trying to plug this part in where HC is being entered. I think its missing an obvious Join or maybe there is a better way to write this. Description is being used after the first BEGIN. I know it needs to also go into my insert somehow, but I'm not sure how or if there is an easier way to do this. Any help is greatly appreciated!!


declare @qualid int
if 1=1
BEGIN
if not exists (select * from medlists where tablename='ProcedureCodeQualifier' and Description = 'HCPC - DEN')
begin
declare @listorder int
select @listorder=max(listorder)+1 from medlists where tablename='ProcedureCodeQualifier'

insert into medlists
select 'ProcedureCodeQualifier',NULL,'HC','HCPC - DEN',@listorder,NULL,NULL,NULL,NULL,NULL,NULL,NULL,@listorder,getdate(),'CYSScript',getdate(),dbo.GetLogonId()

update medlists set dotid=medlistsid where medlistsid=scope_identity()
end

select @qualid=medlistsid from medlists where tablename='ProcedureCodeQualifier' and Description = 'HCPC - DEN'

update procedures set CPTProcedureCodeQualifierMId=@qualid where proceduresid in (8634)
END
ELSE
BEGIN
select @qualid =(select top 1 medlistsid from medlists where tablename='ProcedureCodeQualifier' and Description like 'Health Care Financing Administration Common Procedural Coding System (HCPCS) Codes%')
update procedures set CPTProcedureCodeQualifierMId=@qualid where proceduresid in (8634)
END