- Affects motor neurones with their cell bodies in the spinal cord and/or motor nucleus of cranial nerves in the brain-stem.
- Cause : inherited condition in the Brittany [Peripheral neuropathies] and the Swedish Lapland dog.
- Also occurs in the Pointer, the Cairn Terrier, the Rottweiler, the German Shepherd dog, the Griffon Briquet Vendeen dog and giant-breed crosses.
- Several isolated reports of motor neuron disease in puppies of several other breeds, which are believed to be inherited.
- Signs : progressive neuropathy in pelvic and thoracic limbs.
- Diagnosis : signs, EMG and nerve conduction studies, nerve and muscle biopsy. Definitive diagnosis is made postmortem.
- Treatment : none.
- Prognosis : guarded or poor.
Signs of diffuse lower motor neurone lesion
- Weakness or paralysis.
- Decreased or absent muscle tone.
- Decreased or absent tendon reflexes (although this tends to occur late in the course of the disease, because reflexes can be elicited while there are surviving functional motor neurons).
- Hindlimbs first, then forelimbs, progressing to tetraparesis (forelimbs in German Shepherd dogs).
- Progressive muscular atrophy:
- Distribution of atrophy depends on entity, severity depends on degree of axonal degeneration.
- Respiratory distress (involvement of intercostal muscles).
- Dysphonia and dysphagia can result if there is involvement of brainstem motor nuclei.
- Deformities in distal limbs (muscle wasting and contracted tendons).
Other signs, depending on breed
- Head tremor.
- Muscle fasciculations.
- Weakness of muscles of mastication and the tongue.
- Reduced gag reflex.
- Proprioceptive deficits due to profound weakness.
- Because the sensory system is unaffected, ataxia is not a component of the disease.
- Carpal valgus deformity.
- Carpal flexion due to contracted tendons.
- Intention tremor/limb tremor after exercise.
- Reduced postural reactions.
- Pelvic limb extensor rigidity.
- Episodic weakness.
Causes of progressive paresis/paralysis starting with pelvic limb(s)
- Ascending syndrome [Diffuse progressive myelomalacia].
- Distal denervating disease .
- Degenerative myelopathies .
- Metabolic neuropathies.
- Endocrine neuropathies.
- Neoplastic neuropathies.
- Polyradiculoneuritis. [Polyradiculoneuropathies]
- Toxic polyneuropathies.
- Any cervical cord disease.
- Cervico thoracic tumor.
- Life expectancy depends on the individual entity, but tends to be longer the later the onset of the disease.
Expected response to treatment
- In most instances, clinical signs are inexorably progressive until animals are unable to stand/walk.
- Mild forms of motor neuron disease may be seen, eg unilateral forelimb involvement in German Shepherd dogs in which signs may not progress.
- In Brittany spaniels with the 'chronic' disease, clinical signs may stabilize.
Reasons for treatment failure
- Incorrect diagnosis.
- Inadequate nursing care.