Something like diabetes, blood pressure, thyroid etc which don't have a cure and medicine has to be taken throughout life.
These are chronic illnesses or conditions. From Cambridge Dictionaries:
(of an illness) persisting for a long time or constantly recurring: ‘chronic bronchitis’ Often contrasted with acute
1.1 (of a person) having a chronic illness: ‘a chronic asthmatic’
It is used specifically for the kinds of conditions you mention; for example:
Type 1 diabetes, once known as juvenile diabetes or insulin-dependent diabetes, is a chronic condition in which the pancreas produces little or no insulin . . . . ("Type 1 Diabetes." MayoClinic.org.)
Edit: Wikipedia also has a list of chronic conditions that includes diabetes, hypertension (high blood pressure), and thyroid disease.
Note that the medical definition of chronic may include conditions that persist for as little as 3 months (see, e.g., the US National Center for Health Statistics' definition). I haven't found a medical term for a longer period (perhaps because doctors are generally optimistic that any condition might eventually be cured), but some medical definitions of chronic do specifically note that the condition may persist throughout life (see the Free Dictionary medical entry for a good overview, and the entries pulled from Mosby's Medical Dictionary and the Gale Encyclopedia of Medicine as well as the "Patient discussion about Chronic" for definitions that specify life-long conditions).
I would expect if there was a longer term in common medical use it would appear alongside some of the above discussions and definitions of acute and chronic but I don't see such a word; maybe a medical terminology expert can fill the gap if there is a more obscure term.
One possible alternative is permanent condition, which appears to be a legal term (used for worker's compensation determinations and the like). At least one jurisdiction defines this as a condition likely to last at least two years, so still not actually life-long, and as a legal term I would expect it to vary by jurisdiction.
Finally, as your title asks what to call something that "there is no permanent cure for it" and the body of your question specifically references various medical conditions, I have assumed you are asking about the life-long conditions themselves rather than their potential treatments. If that's incorrect, please edit the question so I can amend or remove my answer.