Sub KillAltText()
Application.ScreenUpdating = False
Dim Rng As Range, Shp As Shape, iShp As InlineShape, i As Long
With ActiveDocument
  For Each Rng In .StoryRanges
    With Rng
      For Each Shp In .ShapeRange
        With Shp
          If .Type = msoGroup Then
            For i = 1 To .GroupItems.Count
              .GroupItems(i).AlternativeText = ""
            Next
          End If
          .AlternativeText = ""
        End With
      Next
      For Each iShp In .InlineShapes
        iShp.AlternativeText = ""
      Next
    End With
  Next
End With
Application.ScreenUpdating = True
MsgBox "Finished updating", vbOKOnly
End Sub