Hole in the Head isn't really a disease. Common also with freshwater Discus, many experts believe it is brought on by poor diet and/or water parameters. If your fish has HLLE you need to check all your water parameters and vary your diet. Its not going to go away with any kind of medicine if your water isn't good or your diet is poor. What kind of fish is this? Make sure all fish get their veggies and make sure angels get their sponges. Soak your food in Zoe or Selcon.
Minor cases will kind of fill in and return to normal. Many serious cases can be treated but the fish will never look the same again!