Neurotransmitter: Tiki

Tiki is a 4 year-old spayed female Maltese referred to Bush Veterinary Neurology Service after one week of 30-60 second episodes of lethargy, shaking and keeping her head down. She became progressively worse, started crying out during the episodes and would intermittently circle to the left.

The owner brought a video of the episode, which showed a two-minute episode of vestibular ataxia, mild left head tilt and holding her head down. Tiki would also hold her right pelvic limb up during the episode and appeared alert and aware (would wag her tail when the owner called her name). Immediately after the episode, Tiki moved normally. Neurologic examination showed evidence of an abnormality in the caudal fossa (caudal cerebrum and cranial brainstem), lateralized to the left. Her intermittent episodes were most likely due to an increase in intracranial pressure, rather than seizure activity.

An MRI of the brain was consistent with diffuse encephalomyelitis and cerebellar herniation. A cerebrospinal fluid analysis was recommended to confirm the diagnosis for inflammatory disease, but considered of increased risk due to the foramen magnum herniation. Despite concerns for her long-term prognosis (due to how severe the changes seen on her MRI and her progressive clinical signs) she has continued to do well on medications.

Presenting Complaint:

Increasing frequency of episodes of keeping her head down and mental dullness, lethargy, decreased appetite, and circling to the left.

Assessment (Neurolocalization):

Left lateralized caudal fossa

1. Dull mentation
2. Tendency to hold head and neck down
3. Circling to the left
4. Vestibular ataxia, with intermittent crossing in all four limbs
5. Decreased placing reactions in the left limbs
6. Pain on palpation over the head

Diagnostics:

An MRI of the brain shows moderate enlargement of all ventricles and a non-contrast enhancing hyperintensity within the cervical spinal cord parenchyma. On the post contrast T1W post sagittal image, the caudal aspect of the cerebellum was herniated through the foramen magnum.

Outcome:

Tiki was administered mannitol (1g/kg) intravenously after her MRI to decrease intracranial pressure. Due to her signalment, examination and MR findings, we were most suspicious of an immune-mediated meningioencephalitis, specifically granulomatous meningioencephalitis (GME). Tiki was admitted to the hospital for empirical therapy for her inflammatory disease. She was started on steroid medication (prednisone 0.5mg/kg PO q12h) and immunomodulatory medication with a CRI of intravenous cytarabine (Cytosar) over 48 hours and cyclosporine (5mg/kg PO q12h). She was also placed on famotidine (0.5mg/kg) for gastroprotection while on the steroid. Tiki was discharged from the hospital two days later with an improved neurologic examination (less compulsive circling, mild ataxia and improved postural reactions).

In the few months after her hospitalization, Tiki has shown progressive improvement and is now neurologically normal. She has not required any additional cytarabine therapy and is currently being maintained on daily cyclosporine and a low dose of steroids, which we have been tapering slowly over the past several months. We suspect that due that her prognosis is good, though relapse in patients with immune-mediated inflammatory central nervous system disease is always possible.

Take Home Points:

1. Having clients videotape episodic neurologic abnormalities can be helpful when considered along with the history and neurologic examination in determining a patient’s neurolocalization. This is especially true in cases like Tiki’s, where the neurologic examination is normal between episodes.
2. Cerebellar herniation is a dynamic process and is observed in patients with an increase in intracranial pressure.
3. The prognosis for immune-mediated brain disease like GME was once poor but with the advent of new medications and protocols, the prognosis is much better. A recent retrospective showed that 60% of dogs were normal and the other 40% much improved on azathioprine, the dogs in this study had an average survival of almost 6 years. At BVNS we use prednisone to manage the acute symptoms but try to replace this medication with immune modulators like azathioprine, cyclosporine, leflunomide and/or chemotherapies like cytosar, procarbazine, and lomustine.

To ask a question related to this case or discuss any aspect of it please email Dr. Hague.

A special thank you to Dr. Jennifer Lauer at the Pender Veterinary Center who referred this case. Dr. Lauer is an Ohio State University classmate of Dr. Hague’s and is now practicing at Valley Veterinary Emergency and Referral Center.

If you would like to download a PDF of the case study, please click here.