So this cat presents with lameness in the rear limbs. We rule out a broken back and herniated disks with radiographs and a myleograms.
Still not knowing what it is, we ultrasound the abdomen and find a huge fluid filled mass. We drained half a liter of pus. We still don't what kind of bacteria it is, since it's so slow growing.
I'll bet you it's Actinomycetes. Yeah had a case of that recently. Took 250 mg of Ampicillin three times daily for 9 months to clear that up.