That is not an Ichthyophthirius cyst. Could be the nematodes parasites Geoff has mentioned. If so, recommend taking frog to veterinary in order to obtain a correct dosage prescription for treatment. In lieu of that; you could try the temporary fix Geoff described.
Both metronidazole and levamisol have been used against nematodes; but correct dosage and treatment duration are important, because applied wrongly, they can do more damage than good. There are other anti-nematode medications to treat fish aquariums; but I have not used them with frogs yet.