Page 210 - Cote clinical veterinary advisor dogs and cats 4th

Atlantoaxial Instability 87

• Intention tremor (i.e., tremor precipitated • Caudal occipital malformation syndrome • In patients being treated conservatively for
(Chiari-like malformation)
by the onset of voluntary movement, such • Vascular event suspected disc extrusion, strict cage confine-
VetBooks.ir • Preservation of strength and postural Additional details on the causes of ataxia are • In patients who knuckle when they walk, Diseases and Disorders
ment is recommended for 4 weeks (p. 555).
as responding to a command)
reactions
provided on p. 1201.
booties should be used for preventing trauma.
• Ipsilateral absent menace response possible
with cerebellar disease DIAGNOSIS Possible Complications
• Head tilt away from the lesion in paradoxical • Trauma resulting from falls associated with
vestibular syndrome Diagnostic Overview ataxia
• Opisthotonos with normal/anxious menta- Diagnosis and initial evaluation of ataxia • Anorexia and dehydration due to incapacita-
tion, thoracic limb extensor rigidity, and depends on performing a careful neurologic tion or nausea
pelvic limb flexion with acute severe lesions exam to demonstrate neurologic deficits that • Respiratory dysfunction with severe cervical
(decerebellate rigidity) localize the lesion to a specific region of the spinal cord lesions
nervous system.
Etiology and Pathophysiology Recommended Monitoring
Proprioceptive ataxia: Differential Diagnosis Follow-up exam and serial diagnostic studies
• IVDD • Orthopedic disease (e.g., ruptured cranial as directed by the patient’s clinical progression
• Cervical spondylomyelopathy/wobbler cruciate ligament, hip dysplasia)
syndrome • Weakness (metabolic, neuromuscular) PROGNOSIS & OUTCOME
• Degenerative myelopathy
• Congenital malformations (spina bifida, Initial Database • Depends on the underlying cause
syringomyelia) • Complete physical and neurologic examination • In general, diseases with an acute onset have
• Intraarachnoid diverticula (p. 1136), including fundic (p. 1137) and a more favorable prognosis than those with
• Fibrocartilaginous emboli otoscopic exam (p. 1144) to precisely localize a chronic course.
• Neoplasia the lesion and guide further diagnostics
• Myelitis • CBC, serum chemistry, urinalysis, thyroid PEARLS & CONSIDERATIONS
• Trauma profile to rule out systemic causes
Vestibular ataxia: Comments
• Idiopathic peripheral vestibular disease (old Advanced or Confirmatory Testing • Accurate identification and characterization
dog, any age cat) • Imaging modalities (radiography, MRI of ataxia are the most important aspects of
• Otitis media/interna [p. 1132], CT, myelography) neurologic localization.
• Vascular event • Cerebrospinal fluid analysis (pp. 1080 and • Diffuse lower motor neuron disease causes
• Encephalitis 1323) essential for the diagnosis of inflam- weakness but not ataxia; affected animals have
• Neoplasia matory disorders a short-stride gait, but careful examination
• Inflammatory polyp (cat, middle ear) • Electrodiagnostics (e.g., brainstem auditory reveals that although they may not have the
• Hypothyroidism (older dog) evoked response) for vestibular diseases and strength to appropriately place their limbs, they
• Chiari-like malformation (caudal occipital suspected brainstem disease are aware of the position of the limbs in space.
malformation syndrome) • Serum and cerebrospinal fluid titers for • When examining an abnormal gait, pay
• Polyneuropathy infectious diseases attention to whether you can predict where
• Toxic (e.g., aminoglycosides, metronidazole), the patient will place the paw next (ortho-
especially topical (ear medication) with TREATMENT pedic) or not (ataxia).
disrupted tympanum
• Thiamine deficiency (cats) Treatment Overview Technician Tips
Cerebellar ataxia: Identify and eliminate the underlying cause; Animals with vestibular dysfunction prefer to
• Abiotrophy referral to a veterinary neurologist is often lie/be restrained on the side to which the head
• Atrophy/hypoplasia (in utero panleukopenia indicated. tilts.
infection in cats, herpesvirus in dogs, others)
• Infectious (feline infectious peritonitis, Behavior/Exercise SUGGESTED READING
distemper) • To prevent falling, access to stairs should be de Lahunta A, et al: Veterinary neuroanatomy and
• Inflammatory (meningoencephalitis: granu- restricted for ataxic patients. Specifically, clinical neurology, ed 4, St. Louis, 2015, Saunders.
lomatous, steroid-responsive, necrotizing) descending stairs can exacerbate the signs of AUTHOR: Greg Kilburn, DVM, DACVIM
• Neoplasia vestibular ataxia. EDITOR: Leah A. Cohn, DVM, PhD, DACVIM

Atlantoaxial Instability Bonus Material Client Education
Online
Sheet
BASIC INFORMATION brainstem. It is most often caused by congenital Epidemiology
malformation of the C1-C2 vertebrae and their SPECIES, AGE, SEX
Definition associated ligaments, trauma, or a combination • Congenital form: toy and small breeds of
Atlantoaxial instability (AAI) is an abnormal of both. dogs, usually ≤ 1 year of age
range of motion occurring between the atlas • Traumatic form: large-breed dogs (rare), toy/
(C1) and the axis (C2), resulting in subluxation Synonyms small-breed dogs, cats (rare)
of C2 relative to C1 and injury to the cranial Atlantoaxial subluxation, atlantoaxial
cervical spinal cord and sometimes the caudal malformation

www.ExpertConsult.com