I don’t have an intrathecal pump, but can see the point of one if your stiffness and / or spasms are making life a misery.
I think the idea of an intrathecal pump is that you can target the Baclofen more effectively, so a much smaller dose is needed to achieve the same effect of a large dose taken in tablet form. This means that you are taking such a reduced amount that the effect of muscle weakness is avoided (once you get the pump).
Do you mean that before the pump can be fitted you have to increase your tablet dose to 90mg over day? And that’s to ensure that the intrathecal dose will do what you need it to?
If that’s the case, then as you’ll be increasing very gradually to the 90mg, you may not see much difference in muscle weakness, but that really depends what dose of Baclofen you’re starting from. I would imagine that to switch to intrathecal you’d already be on a fairly high dose? I currently take 60-70 mg per day, I was taking at least 80 mg until I started taking Cloneazepam, which meant I could reduce the Baclofen. I’ve not especially noticed more muscle weakness or fatigue from increasing the dose, or conversely, when I decreased the dose down to 60 mg.
But, as Jan says, try the PP forum to get views on the actual pump.