Cerebellum: tremors & movement disorders ✔️

Tremor

• involuntary rhythmic oscillatory movement of any body part

• can vary in frequency & amplitude

Myoclonus

• repeated arrhythmic shock-like jerks

• sudden contraction of a muscle group followed by immediate relaxation

• often associated w/distemper, can be caused by any meningoencephalitis

Tetanus vs tetany

• continuous contraction of extensor mm.

vs

• intermittent & variable contraction of extensor mm.

Myotonia

• sustained mm. contraction w/delayed relaxation

Fasciculation

• contraction of mm. fibers associated w/motor unit (no limb/body movement)

Dyskinesia

• involuntary alteration in movement lasting for long periods of time

• type of movement disorder caused by lesion in basal nuclei

• often mistaken for seizures

• differences: pts conscious during episode, may last seconds-hours, no post-ictal period, no facial involvement

• may be hypo or hyper

  • ex: limb hyperflexion

• Tx: gluten free diet

Dystonia

• sustained involuntary contraction of a group of mm. producing abnormal postures

• often associated w/dyskinesia

Ddx for tremors

• cerebellar Dz (congenital vs acquired)

• steroid responsive tremor syndrome

• metabolic Dz (hypocalcemia vs hypoglycemia)

• toxins/medications

• myelin disorder

Dx approach for tremors

• signalment: breed + age

• onset: acute (intoxication, encephalitis, steroid responsive tremor syndrome, metabolic) vs chronic (congenital)

• episodic vs constant

• assessment of characteristics (area involved, frequency + amplitude)

• other signs

Cerebellar hypoplasia

• often secondary to intrauterine infections (panleukopenia, herpesvirus) or may be genetic

• classic cerebellar signs starting when pt starts to walk, non-progressive

• Dx: MRI, histopath, often presumptive based on non-progressive signs

• Tx: none

Cerebellar abiotrophy

• spontaneous cell death mostly affecting Purkinje cells, often go on to affect other areas of the nervous system

• genetic or immune-mediated, onset + progression vary by breed

• Dx: signalment + signs, usually histopath @ necropsy

• Tx: none

Meningoencephalitis

• any inflammatory CNS Dz can cause cerebellar signs w/multifocal CNS lesions

• may be caused by distemper, FIP, herpesvirus, Neospora, or immune-mediated

  • steroids contra-indicated for infectious Dz

Neosporosis

• protozoal Dz, causes progressive cerebellar signs in adult dogs

• should not immunosuppress (don’t use steroids)

• Dx: serology, high CK

Cerebellar neoplasia

• uncommon

• usually causes asymmetric signs

• medulloblastomas, oligodendrogliomas

Steroid responsive tremor syndrome

• acute onset of generalized high-frequency tremors + fever, likely due to immune-mediated encephalitis

  • less common signs: head tilt, opsoclonus, decreased menace

• causes: Mycotoxin, hypocalcemia, hypoglycemia

• mostly seen in young small dogs

• Dx: imaging useless, CSF may show mild mononuclear pleocytosis

• Tx: steroids

Head tremor syndrome

• seen in bulldogs, Boxers, labs, Dobies

• may be focal epileptic seizures or paroxysmal movement disorder

• do careful neuro exam, can be structural brain Dz

• may be caused by tumors or meningoencephalitis

Tremor-causing toxins

• moldy foods (mycotoxins)

• theobromine

• organophosphates, carbamates

• medications: metoclopramides, metronidazole

Metabolic Dz

• hypocalcemia

• hypoglycemia: rapid glycopenia

• Addison’s

• hepatic encephalopathy

Canine leukodystrophies

• uncommon breed-related Dz, mostly seen in young dogs

• myelinolytic disorders, disturbs central myelinogenesis

Hypomyelination vs dysmyelination

• incomplete formation of myelin

• genetic Dz, spontaneously resolves

vs

• abnormal myelination

• much worse prognosis

both uncommon conditions that cause high amplitude tremors that worsen w/movement/stress