Paresis and Ataxia in Two or Four Limbs
Quadriparesis and hemiparesis are seen with lesions affecting the mid to caudal brainstem (midbrain, pons, medulla oblongata) or the cervical spinal cord (C1 to T2 spinal cord segments).
Quadriparesis can also be seen in generalized peripheral nerve or muscle disease, discussed later. Paraparesis results from disease lesions of the spinal cord affecting segments T3 to S2 or the peripheral nerves to the pelvic limbs. Disease of the forebrain does not produce appreciable paresis and ataxia when the animal is walking in a straight line on a level surface, but these signs may become apparent in the limbs contralateral to the lesion when the animal is asked to circle, back, step over obstacles, or walk on a slope. Localization of the lesion when signs of paresis and ataxia are present depends on the assessment of muscle mass and tone, spinal reflexes, and evaluation of brainstem function; the last is determined by the presence or absence of signs such as altered mentation and cranial nerve deficits.■ TABLE 8.11
Diseases of the Brainstem and Cranial Nerves
| Disease | Location | Clinical Signs and Laboratory Findings |
| Nonrabies viral | Multifocal brainstem, | Head tilt, nystagmus, circling, ataxia, tongue paralysis, |
| encephalomyelitis, rabies, | particularly medulla | anisocoria, dilated nonresponsive pupils, strabismus, |
| malignant catarrhal fever (cattle only) | oblongata | lingual paralysis, dysphonia, dysphagia; CSF may show pleocytosis (mainly mononuclear cells) and high protein concentration |
| Listeriosis (ruminants, | Multifocal brainstem, | Circling, head tilt, facial paralysis, stridor, stertor, |
| horses [rare]) | particularly basal ganglia, metencephalon, and medulla oblongata | dysphagia, obtundation, coma, convulsions, ataxia; CSF shows pleocytosis (mainly mononuclear) and a high protein concentration |
| Thromboembolic meningoencephalomyelitis (cattle) | Multifocal brainstem | Circling, nystagmus, head tilt, strabismus, tongue paralysis, dysphagia, facial paralysis, coma, convulsions, obtundation; xanthochromic CSF with increased neutrophils and protein concentration |
| Peripheral vestibular disease | Petrous temporal bone, membranous labyrinths, vestibulocochlear nerve, often accompanied by facial nerve paralysis | Head tilt, circling, or leaning toward lesion side; ventrolateral strabismus on ipsilateral side; dorsomedial strabismus on contralateral side; nystagmus (usually horizontal and constant) |
| Verminous encephalitis | Multifocal brainstem, most commonly thalamus | Circling, nystagmus, head tilt, strabismus, tongue paralysis, facial paralysis, obtundation, coma, convulsions, depression, proprioceptive deficit, bradycardia, salivation, head pressing, blindness; high protein concentration and increased nucleated cell count in CSF |
| West Nile virus | Multifocal brainstem | Fasciculations of neck and facial muscles in addition to the other signs |
| Equine protozoal | Multifocal brainstem and | Seizures, head tilt, facial paralysis, circling, nystagmus, |
| myeloencephalitis | cerebrum | dysphagia, facial paralysis, blindness, ataxia, paresis, hyporeflexia, hyperreflexia |
| Space-occupying mass | Cerebellopontine angle; | Head tilt, strabismus, proprioceptive deficit, facial analgesia, |
| Tumor, abscess | cranial nerves V, VII, and VIII | jaw drop, obtundation, coma, strabismus, nystagmus, hyperreflexia, hypertonia, falling or circling toward affected side, blindness on contralateral side, tongue paralysis, hemianopsia, bradycardia, coma, convulsion |
| Horner’s syndrome | T1 to T3 motor neurons (gray matter), spinal roots, vagosympathetic trunk, sympathetic UMN of spinal cord (tectotegmentospinal), periorbita | Miosis, lack of nasal sweat (cattle only), ipsilateral facial swelling (horses only) |
| Guttural pouch mycosis (horses) | Guttural pouch | Dysphagia, head shyness, headshaking, roaring, dysphonia, protrusion of the tongue from the mouth, epistaxis, head tilt, nystagmus, facial sweating, shivering, Horner’s syndrome, colic, facial paralysis |
CSF, Cerebrospinal fluid; UMN, upper motor neuron.
Quadriparesis and ataxia with normal muscle mass and tone and normal to increased spinal reflexes can be explained by a lesion of the descending and ascending tracts in the brainstem or spinal cord segments C1 to C5. Note that such a finding does not exclude multifocal lesions within the same areas of the CNS.
Presence of clinical signs of brain disease indicates that the lesion (if singular) is in the brainstem, as described earlier. Lesions in the midbrain cause contralateral postural and proprioceptive deficits, whereas those in the medulla oblongata cause ipsilateral signs. Cerebellar disease causes head, neck, truncal, and limb ataxia, without limb weakness. Lesions of the forebrain (thalamus and cerebrum) cause minimal to no paresis or ataxia when the animal moves on a level surface, but contralateral subtle proprioceptive and postural reaction deficits are present. Altered mentation and other signs of forebrain disease such as compulsive circling or central blindness are expected. Animals with spinal cord disease have normal mentation. The clinical signs shown by such patients depend on the location of the lesion and the relative amount of damage to gray (cell bodies) and white (myelinated spinal cord tracts) matter. Loss of white matter affects upper motor neurons and proprioceptive and other sensory pathways, whereas gray matter damage produces lower motor neuron deficits. The sensory losses manifest as either proprioceptive deficits or loss of cutaneous sensation. Spinal cord diseases may be localized to one of the following five regions: high cervical (C1 to C5), cervicothoracic (C6 to T2), thoracolumbar (T3 to L2), lumbosacral (L3 to S2), and sacrococcygeal (S3 to Cd5) regions. Tables 8.4 and 8.5 list the peripheral nerves and the spinal segments that innervate them.
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