As they say, the devil is in the details!
Scarlet fever is a complication of a streptococcal bacterial infection. In the pre-antibiotic (or early antibiotic) days, such bacterial infections could lead (among other things) to severe ear infections, involving the bone behind the eardrum (the mastoid). Such patients were often left with chronic ear drainage due to infection in the mastoid, as well as holes in the eardrums. In many cases, there was little left of the eardrums. In other cases, surgery was done without reconstruction of the eardrum to get the infection under control.
Patient who have had a "radical mastoidectomy" also have no eardrums at all. The entire middle ear cleft (the drum, the bones, and the bony air cells behind the ear) have been drilled away, leaving a large cavity with skin directly over the opening to the inner ear.
Most ENT doctors would not allow diving after a radical mastoidectomy, or with open perforations, because it may not be possible to determine ahead of time whether or not the pressure changes would cause inner ear damage, leading to permanent deafness. There is even the chance of air being trapped around the brain (pneumocephalus, which has been reported in some patients with chronic ear disease who have been exposed to pressure changes).
Every patient is different, and there may be some patients who are many years out from a mastoidectomy and who can tolerate the pressure change due to scarring, etc... but I am not sure how you would determine this ahead of time. Patients who have had surgery involving the path to the inner ear (such as a stapedectomy) should also not dive for similar reasons.
Unlike Eustachian tube problems, where you would know from the pain whether or not you can safely equalize, the first sign of a problem with the inner ear could be a fistula (leakage of inner ear fluid), resulting in disabling vertigo, complete deafness or worse.
A patient who has had a tympanoplasty (a reparied hole in the eardrum) may be OK to dive as long as it is well healed and he or she can safely equalize pressure (best to try this in a pool first!).
Here is a good summary of these ENT diving issues:
journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=450631
Mike
