The issue with 22 digits of precision in DECIMAL is that MATLAB's default number type is DOUBLE which really can only handle around 17 digits at which point the number system itself cannot distinguish the numbers. The import functions are rounding to the nearest double value.
1.000000000000000000000001 is the same as 1.0
If the data are all integers, you can specify int64/uint64.
>> A = readmatrix(filename,'OutputType','int64')
If not integers, than Walter's answer is the best you can do.