Overall, sounds like a great vet visit! I'm thrilled to read this, Pauline. This vet sounds like a "keeper".
Somogyi..... You can read up on it, but bottom line is that it is a theory developed nearly 100 years ago, and at best, today, it is considered "suspect" as far as being a valid theory.
What you are seeing, when Teronto shows you higher numbers, is a perfectly natural instinctive reaction to low BG numbers. His body is designed to self-protect itself against a rapid or big drop in BG levels. Just about every cat on insulin does that. A diabetic cat's body becomes used to above normal BG numbers, and many times, if they drop down to perfectly safe "normal" levels, the instincts kick in. Because "normal", to him, is not "normal", if that makes sense. When the insulin pushes him down into normal ranges, it is doing its job - the job that his pancreas would be doing if it were working correctly. But his system no longer feels comfortable with "normal", so it produces glucagon, glycogen, and other hormones that in effect dump "sugar" into his bloodstream to raise the BG to a level that feels "normal". Sometimes it really dumps, and a kitty can go from green numbers to red numbers in a matter of hours. It's actually a good thing when their BG goes down into the normal range, and the more often it happens, the more chance their systems will "relearn normal", and when that happens, the bouncing up and down seems to happen less often, or less severely.
Some people refer to this as "somogyi". My understanding of somogyi rebound is that it is something that becomes chronic, and the numbers continue to spiral up and up. I may not understand it perfectly though. I think the major issue is that people seem to use "somogyi", "bouncing" and "rebound" interchangeably, when really they are all slightly different concepts. Most people (not here however) suggest that the treatment to correct these ups and downs is to reduce the dose or stop the insulin completely like your vet suggests. From what I have observed from reading here, that usually fails as a strategy, and the dose ends up having to go right back up, or maybe even needs to go higher until the numbers start to come back down again.
Today's cycle shows that .75u worked really really well, a little bit too well in fact. That's why the protocol calls for an automatic reduction in dose because at this point, .75u is more than is needed. That dose should keep his numbers from getting worse, and should avoid another episode like today. Eventually however, the same sort of thing could happen on .5u, because as this is going on, his body is getting better. His numbers each day will tell you what the reduced dose is doing for him, and they will indicate when it is time to (hopefully) reduce the dose again.
There are a lot of people here who have been dealing with FD for a lot longer than I've been aware of the disease. They'll probably be able to explain all of this better than I can, and I'm sure they'll chime in. My opinion - Teronto is doing really well, and Lantus is working very well for him. He's on a really small dose of insulin, and with the weight gain, and your observations that he looks better overall, I see lots of reason for you to feel very encouraged.
Carl
