Midbrain (rostral brainstem) disease Flashcards
How frequent is midbrain disease in cats
Midbrain (or mesencephalic) disease is uncommon in feline medicine
What is the main cause of midbrain disease
Midbrain disease is usually secondary to head trauma
Previously, it was seen in association with thiamine deficiency, which is now quite rare)
What are the clinical signs of midbraain disease
May have an altered state of consciousness
If the oculomotor nucleus is involved, have mydriasis on the ipsilateral side
- may also have ventroloteral strabismus and dropping of upper eyelid
May rarely have visual and menance deficits contra-laterally if there is a lesion in the lateral geniculate body
May see central neurogenic hyperventilation
Lesions in the interpeduncular area (ventral midline) may cause “obstinate progression” where the cat is seemingly unable to discontinue an initiated motor movement (e.g., walking into walls and head pressing)
May have decerebrate posturing
Diffuse midbrain disease may result in bilateral pupillary myosis, that gradually changes to fixed pupils (this holds a grave prognosis)
UMN signs and postural reaction sdeficits to all four limbes or limbs on the contralateral side to the lesion
What are your main differentials for midbrain diseases
Neoplastic
- Primary CNS tumors
- Extension of other intracranial tumors
Infectious
- Viral (e.g., FIP)
- Protozoal (e.g., toxoplasmosis)
- Fungal (e.g., cryptococcosis)
- Bacterial (e.g., abscessation)
Vascular
- Trauma
- Other (e.g., emboli)
Nutritional
- Thiamine deficiency (usually has concurrent signs of bilateral central vestibular disease)
Other
- brain herniation secondary to increased intracranial pressure
Explain why thiamine deficiency has declined for pets fed with commercial food
The incidence of thiamine (Vitamin B1) deficiency has declined now that manufacturers supplement canned cat food
Explain why thiamine deficiency has re-emerged with the practice of feeding pet-grade minced meat (e.g., kangaroo, beef, …)
Thiamine deficiency has re-emerged with the practice of feeding pet-grade minced meat because it has been preserved with sulfur dioxide
Can you give another reason (except for non-supplemented cat canned food and pet-grade mince meat) to thiamine deficiency
Feeding an exclusively raw-fish diet could lead to thiamine deficiency because of thiaminase content in fish
What are the lesions induced by thiamine deficiency
Thiamine deficiency causes hemorrhagic necrosis of the oculomotor and vestibular nuclei, the caudal colliculus and the lateral geniculus nucleus due to the high thiamine requirements of these areas of the brain
What is thiamine used for in the body
One of the body’s uses for thiamine is as a component of thiamine pyrophosphate, an enzyme utilized in the metabolism of carbohydrates and amino acids
It is also used in the biosynthesis of some neurotransmitters
What are early clinical signs for thiamine deficiency
Early signs include anorexia and vomiting with bilateral vestibular dysfunction and active cervical ventroflexion
What are the late signs for thiamine deficiency
As the disease progresses bilateral mydriasis, blindness, seizures, coma, and eventually death is observed
- in some cases, seizures may be the only, or primary clinical manifestation
- thiamine deficiency should be considered in cats presented for seizuring or with multifocal neurological signs, even if they are fed a commercial diet
How is a diagnosis of thiamine deficiency made
Diagnosis is usually made via:
- observation of specific clinical signs
- coupled with a history of ingestion of a thiamine-depleted diet
- MRI findings are characteristics and include:
- hyper-intensity of the lateral geniculate nuclei, caudal colliculi, periaqueductal grey matter, and facial and vestibular nuclei
- high profile liquid chromatography, if available, can be used on whole blood samples to compare thiamine diphosphate levels of suspected cases to control animals
How can you track response to thiamine deficiency therapy
MRI can be used to track response to therapy
Explain why thiamine deficiency can still occur in animals fed a combined diet if mince is added to every meal
Sulfur dioxide (food additive 220,221) in pet-mince can destroy the thiamine in vitamin supplements and commercial food thus the condition can still occur in animals fed a combined diet if mince is added to every meal
Owners should be advised to purchase human-grade meat that does not contain preservatives if mince is to be included as a regular part of the cat’s diet
What is the treatment for thiamine deficiency
Treatment involves:
- the administration of thiamine (100-250 mg q12h)
- provision of a well-balanced commercial diet
What is the prognosis for thiamine deficiency
If caught early enough, the neurological lesions induced by thiamine deficiency can be readily reversed
More severely affected animals may be permanently affected
