--hyperreflexia is not as common in neuropathic conditions as hyporeflexia, but it still isn't something to ignore; as was indicated, the most likely explanation is some sort of dysfunction of the spinal cord that causes the muscles to contract too briskly. Rose has talked about hyperreflexia being common in the spinal cord degeneration that is involved in advancing B12 deficiency. Spinal MS can definitely cause it, too.

There are also syndromes that have primarily peripheral effects that have secondary central effects that can cause this, such as Niacin deficiency.

I haven't seen this mentioned with Sjogren's, except in the rare cases where CNS involvement might cause transverse myelitis (and I've only seen the Washington University research website mention that).

It's possible, though, that this is related to arthritic impingment in the spine. The most common casue that I know of, though, after actual spinal injury, is medication side effect--and this is quite common. Time to look at all your meds and the possibility of interactive effects (and I'm glad you'e getting the MRI).