CNS Idiopathic Conditions - Pathology

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Idiopathic Epilepsy

  • A seizure is a brain disorder which manifests as paroxysmal cerebral dysrhythmia.
    • The episode has a sudden onset and ceases spontaneously.
    • Seizures tend to recur.
  • In epilepsy, individuals appear to have a low seizure threshold.
    • This predisposes their neurons to depolarize of their own volition.
  • "Idiopathic epilepsy" is said to occur when no other cause of seizuring is apparent.

Pathogenesis

  • All seizures arise from a small group of neurons that periodically and spontaneously depolarize.
  • In addition to being idiopathic (i.e. low seizure threshold), this sudden, uncontrolled neuronal discharge can occur due to:
    • Structural causes
      • Neoplasms
      • Inflammation
      • Trauma
    • Biochemical causes
      • Hypocalcaemia
      • hypoglycaemia
      • Hepatic encephalopathy.

Pug Dog Encephalitis

  • A non-infectious central nervous inflammatory disease
  • Affects pugs.
    • Similar conditions are seen in yorkshire and maltese terriers.
  • Officially known as necrotising meningoencephalitis of small dogs.
  • Characterised by histological forebrain inflammation and necrosis.
  • The disease is uniformly fatal.
    • Corticosterid treatment has no effect.

Granulomatous Meningoencephalitis

  • A non-infectious central nervous inflammatory disease
  • May occur as:
    • A disseminated disease
    • A focal mass lesion
    • A primary occular disease
  • Brainstem signs are common, although the forebrain is primarily affected.
  • May be incorrectly diagnosed as lymphoma.
  • Changes are apparent in the CSF.
    • There is usually a mononucloear pleocytosis.
    • Sometimes only protein is elveated.
  • Diffuse inflammatory changes or a mass lesion will be seen by advanced imaging.
    • However, biopsy is required for a definative diagnosis.
  • Life span is between 6 months and 1 year from diagnosis.

Polyneuritis equi

  • A non-infectious central nervous inflammatory disease
  • Polyneuritis equi (PNE) is an uncommon disease which affects mature horses
  • Formerly known as 'cauda equina syndrome' or 'cauda equina neuritis'
  • May occur as:
    • A disease effecting the spinal nerve roots and ganglia of the cauda equina.
    • A disease effecting the cranial nerves.
  • Cauda equina disease is characterised by progressive loss of anal tone, tail paralysis, urinary and/or faecal incontinence, urine scalding of the hindlimbs, hyperaesthesia and muscle fasciculations over hindquarters.
  • If the pelvic nerve roots are also involved, there may be changes in hindlimb gait.
  • Cranial nerve signs may be apparent, including signs associated with facial nerve paralysis.
  • Changes in the CSF are often non-specific.
    • There is usually a moderate mononucloear pleocytosis.
    • Protein is usually elveated.
  • Histologically, the disease presents as a severe, chronic, destructive lymphocytic and histiocytic polyradiculoneuritis.
  • Pathogenesis not completely understood, but considered to be caused by a T-lymphocyte mediated response to myelin, followed by destruction of myelin and axons by macrophages
  • Disease appears similar to:
    • Guillain-Barré Syndrome (GBS), an autoimmune demyelinating diease in humans
    • Experimental allergic neuritis (EAN) in laboratory animals
  • Important differential diagnoses for progressive neurologic signs effecting the bladder, rectum, perineum, tail, penis and hindlimbs in horses include:
    • Equine herpesvirus-1 myeloencephalopathy
    • Sacral/coccygeal trauma
    • Equine motor neuron disease
    • Abberant parasite migration (e.g. Strongylus spp.)
    • In endemic areas, Sarcocystis neurona myelitis (equine protozoal myelitis), rabies and rhodococcus equi myeloencepahlitis should also be considered.