they get a type of lateral line erosion that can present on the head and also on the rest of the body. this is usually due to a nutritional deficiency and/or water quality issue. the best way to treat (and they do recover quite well) is by increasing water changes...do larger volume changes and do them more frequently (try once a week at least, more if you can). along with this, you should try to work some vegetable matter into their diet, i have found that algae wafer work great for this.
this combination of treatment has worked whenever i've had lungfishes with these issues. hope that helps and good luck--
--solomon
PS-- what do you feed the fish now?