Sub test()
Dim DerLig As Long, DerCol As Integer, Plage As Range, c As Range, PlF(), i As Long
DerLig = Range("A" & Rows.Count).End(xlUp).Row
DerCol = Range("A1").End(xlToRight).Column
Rows("2:" & DerLig).ClearFormats
Set Plage = Range("A2:A" & DerLig).SpecialCells(xlCellTypeVisible)
i = 1
For Each c In Plage
ReDim Preserve PlF(1 To Plage.Cells.Count, 1)
PlF(i, 0) = c
PlF(i, 1) = c.Row
i = i + 1
Next c
For i = LBound(PlF) To UBound(PlF) - 1
If PlF(i, 0) <> PlF(i + 1, 0) Then
Range(Cells(PlF(i + 1, 1), 1), Cells(PlF(i + 1, 1), 2)).Font.Bold = True
Range(Cells(PlF(i, 1), 1), Cells(PlF(i, 1), DerCol)).Borders(xlBottom).Weight = xlMedium
End If
Next i
End Sub