Return column header, max value, 2 values same

I have the following spreadsheet, for which I wish to identify the highest number in a row, then return the corresponding column header. For example, for the bottom row, the highest number is 10, and the following formula: =INDEX($A$1:$D$1,MATCH(MAX(A7:D7),A7:D7,0)) returns TP1 as the highest. However, there are 2 values of 10 (the other being in TP4 column), but the above formula only returns the first instance.

Is there any way to make excel return all column headers, in instances where there are two or max values the same? For example, listing them seperated by commas would be ideal.

TP1 TP2 TP3 TP4
1 2 3 4
3 3 1 2
2 2 3 8
5 5 7 5
7 3 3 2
10 7 8 10

Thanks in advance for your help!