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Tremor syndrome in cats

Mauler DA, van Soens I, et al. Idiopathic generalized tremor syndrome in two cats.  J Feline Med Surg. 2014;16(4):378-80.

Idiopathic generalized tremor syndrome (IGTS), formerly known as idiopathic cerebellitis, steroid-responsive tremor syndrome, or “little white shaker syndrome” is an acute tremor syndrome responsive to glucocorticoids that has long been recognized in young small-breed adult dogs. Initially this disease was observed in small breed white dogs such as West Highland white terriers, poodles, and Maltese, hence the name “little white shaker syndrome”, but it is actually known in many other small breed dogs with a variety of coat colors.  This case report describes suspected IGTS in two domestic shorthair cats, which are the first cases of the syndrome reported in cats.

The tremors associated with IGTS are intention tremors; they worsen with movement, and decrease at rest. Other clinical signs can include opsoclonus (irregular, rapid eye movements), head tilt, hypermetria, and a decreased menace response.  Paresis is a less common finding in affected animals.  After the first two to three days, IGTS is nonprogressive, and spontaneous remission may occur.  On necropsy, dogs with IGTS demonstrate mild, nonsuppurative inflammation of the nervous system, not just limited to the cerebellum.  Mild to moderated mixed or mononuclear inflammatory changes in the cerebrospinal fluid (CSF) are found in about half of affected canines.  The etiology of this disease in dogs is suspected to be viral or immune-mediated, but may be different in cats and is unknown in this species.  As in dogs, identification of this disease in the two cats of this report was a diagnosis of exclusion as well as based on clinical signs and response to therapy.  Affected dogs are usually treated with immunosuppressive doses of corticosteroids; diazepam may be added to reduce the severity of the tremors.  In many cases treatment may be discontinued after 1-3 months, but some dogs may need lifelong treatment to prevent relapses.

Both cats discussed in this report were young male neutered domestic shorthair cats; one patient was 10 months old (cat 1) and the other, 17 months old (cat 2).  The cats were from different households and lived strictly indoors; the 10 month old cat had a predominantly white coat, and the 17 month old cat had a completely white coat.  They were on commercial feline diets, and both had received vaccinations for feline panleukopenia, viral rhinotracheitis, and calicivirus a number of months before developing clinical signs; neither was on medications of any kind in the four months prior to onset of the tremor disorder.  Normal CSF findings were demonstrated in both patients. Exposure to tremorgenic toxins such as permethrin, organophosphates, and carbamates was considered highly unlikely in both cats based on their history and lifestyle.

In cat 1, infectious diseases that may be associated with tremors in cats such as toxoplasmosis, feline leukemia (FeLV), feline immunodeficiency virus (FIV), feline coronavirus, Borna virus, and crypotococcosis were excluded using laboratory testing.   Cat 1 was negative for FeLV and FIV based on ELISA testing of a blood sample, and the other infectious diseases were ruled out using PCR testing on a CSF sample.  No abnormalities were detected on a brain MRI of cat 1.  Cat 2 did not undergo infectious disease screening or MRI evaluation, but had a normal complete blood count (CBC) and biochemical screen. The diagnosis of IGTS in cat 2 therefore was presumptive, and partially based on this patient’s excellent response to treatment.  A mild leukocytosis was the only abnormality found on the CBC of cat 1; this cat’s biochemical screen was unremarkable.  Both cats underwent an electrophysiological examination, including electromyography, motor nerve conduction velocity study, and repetitive nerve stimulation evaluation. All of these tests were normal in both cases, ruling out neuromuscular disorders as a cause of the tremors.

Cat 1 received subcutaneous prednisolone and intravenous diazepam therapy due to the initial severity of clinical signs and improved within a few days of initiation of treatment. He was sent home on oral prednisolone and diazepam.  This cat had normal physical and neurological evaluations, CBC, and serum biochemistry four weeks later.  As the medication was tapered, the cat relapsed and mild but generalized tremors returned.  The owners elected to maintain the cat on 0.5 mg/kg of prednisolone every other day; the tremors disappeared completely after 6 months of treatment, and the cat remained in complete remission at the time of last follow-up, which was 14 months after diagnosis. Cat 2 received oral prednisolone and diazepam from the start of therapy; he improved after 2 days and was normal one week later.  His medications were discontinued 8 weeks after presentation and was in complete remission at the time of last follow-up, which was also 14 months after diagnosis.  Liver function in both cats was monitored due to the use of oral diazepam, and no abnormalities were identified. [PJS]

See also:
Penderis J.  The wobbly cat.  Diagnostic and therapeutic approach to generalized ataxia.  J Feline Med Surg. 2009; 11(5):349-59.