How often do you hear "my dog's legs shake when s/he stands?" (Okay, perhaps not as often as I do...but I'm going to assume you hear it at least a LITTLE bit of the time!)
Etiology
Orthostatic tremors can be primary, meaning the tremor is the disease itself. This is suspected to originate from the cerebellum or brainstem but is still, as of now, unknown. The disease is progressive therefore neurodegenerative causes have been considered.
Tremors that are associated with another neurologic disease are termed OT-Plus and include an assortment of spinal cord compressive diseases such as Wobbler's or LS disc herniation. The tremors with OT-PLUS are therefore suspected to be associated with weakness driven from the primary myelopathy, not a disease process in its own right.
Description
When rising to stand, during standing, or occasionally when rising to sit, dogs will exhibit a fine, involuntary tremor in pelvic limbs (most commonly), all four limbs (second most commonly) or thoracic limbs only (rarely). These abate when recumbent, or in active motion (walking, running). Specific awake electrodiagnostic testing confirms the disease but the clinical suspicion is high with the history alone. Orthostatic tremor (OT) has been described in large or giant breed dogs only. Signs begin between 9 months and 2 years of age for OT, and a bit older for OT-plus. In fact, Retrievers and older age were associated factors with OT-plus in a recent retrospective study reporting on orthostatic tremors. (10.1111/jvim.16328.)
Treatment
Okay this is super interesting to me (and hopefully you)! This data is for primary OT, not OT-plus.
Phenobarbital/primidone - 15/15obtained remission (2 lost to follow up)
Gabapentin/pregabalin - 25/29obtained remission (3 lost to follow up)
Clonazepam - 5/6 obtained remission (1 lost to follow up)
Improvement was more likely to be partial than complete resolution (7:3) but some improvement was noted. Interestingly, clonazepam is reported to be the drug of choice for human OT and yet the response to treatment is minimal compared to what we see with our canine patients.
Why do these treatments help? Unknown. It isn't a convulsive disorder therefore these medications are helping from a different angle. I'll keep you posted as we hear more!
Take away from this:
Young, large or giant breed dogs with tremors may have OT
Look for an underlying cause if signs onset at an older age, especially in a retriever breed
Try one of the treatments listed, let me know what you think!
As always, thanks for reading. Please let me know if you have any questions about OT, or any other case you are evaluating.
I appreciate your business and look forward to continuing to work with you and your team!