SQL Server 2012 :: Query To Find The Difference In Values From Previous Month?

I have my sql tables and query as shown below :

CREATE TABLE #ABC([Year] INT, [Month] INT, Stores INT);
CREATE TABLE #DEF([Year] INT, [Month] INT, SalesStores INT);
CREATE TABLE #GHI([Year] INT, [Month] INT, Products INT);
INSERT #ABC VALUES (2013,1,1);
INSERT #ABC VALUES (2013,1,2);

[code]....

I have @Year and @Month as parameters , both integers , example @Year = '2013' , @Month = '11'

SELECT T.[Year],
T.[Month]

-- select the sum for each year/month combination using a correlated subquery (each result from the main query causes another data retrieval operation to be run)
,
(SELECT SUM(Stores)
FROM #ABC
WHERE [Year] = T.[Year]
AND [Month] = T.[Month]) AS [Sum_Stores],
(SELECT SUM(SalesStores)

[code]....

What I want to do is to add more columns to the query which show the difference from the last month. as shown below. Example : The Diff beside the Sum_Stores shows the difference in the Sum_Stores from last month to this month.

Something like this :

+------+-------+------------+-----------------+-----|-----|---+-----------------
| Year | Month | Sum_Stores |Diff | Sum_SalesStores |Diff | Sum_Products |Diff|
+------+-------+------------+-----|------------+----|---- |----+--------------|
| 2013 | | | | | | | |
| 2013 | | | | | | | |
| 2013 | | | | | | | |
+------+-------+------------+-----|------------+--- |-----|----+---------| ----