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4.4.5 Electrodiagnostic Examination
Electrodiagnostic studies assess the integrity of muscles and nerves through recording action
potentials. The two most commonly performed electrodiagnostic studies include electromyogra-
phy (EMG), which measures spontaneous electrical activity of muscles, and nerve conduction
velocity (NCV), which evaluates the function of a motor or sensory nerve by measuring the veloc-
ity of an evoked action potential along its length. General anesthesia is required for most electro-
diagnostic tests to minimize both movement artifacts and patient discomfort. A detailed
discussion of electrodiagnostic testing can be found in the literature (Cuddon 2002; Dickinson
and Lecouteur 2002).
Collectively, electrodiagnostic studies are useful screening tests to confirm dysfunction in the
muscle or nerve. Although these tests do not diagnose specific PNS disorders, because orthopedic
disease will not cause abnormalities on electrodiagnostic studies, they can aid in distinguishing if
equivocal signs of lameness (e.g. pain or atrophy) are caused by neurologic or orthopedic disease.
For example, if muscle atrophy is present, EMG will be normal if the cause is disuse atrophy rather
than neurogenic. Thus, the distribution of abnormalities can be mapped out through testing of
specific muscles and nerves, the results of which guide additional testing needed, like muscle and
nerve biopsies, so that only tissue from abnormal regions is collected.

4.4.6 Cerebrospinal Fluid Analysis
Cerebrospinal fluid (CSF) is contained in the ventricular system and subarachnoid space, where it
bathes the brain and spinal cord, including nerve roots. It is produced in the ventricles by the cho-
roid plexus and ependymal cells as well as the brain tissue.
Analysis of CSF often contributes to a diagnosis but rarely gives a specific diagnosis, much like
abnormal complete blood count (CBC) or serum chemistry results. Thus, it is very sensitive for
detecting CNS disease but in most cases, it is not very specific. Indications for CSF collection
include any disease affecting the brain, a spinal cord lesion not definitively diagnosed on advanced
imaging, and lesions suspected to affect the spinal nerve roots (radiculopathies), which are the
only portion of the PNS still enclosed in meninges.
Collection of CSF is performed either from the cerebellomedullary or lumbar cistern; typically, the
location that is nearest or caudal to the suspected location is selected. A normal CSF does not
exclude neurologic disease. For example, if a disease process does not involve the meninges, it may
not be evident on CSF analysis. Descriptions of how to perform and interpret CSF fluid analysis
can be found elsewhere (Di Terlizzi and Platt 2009; Dewey and Da Costa 2016).

References

Cuddon, P.A. (2002). Electrophysiology in neuromuscular disease. Vet Clin North Am Small Anim
Pract 32 (1): 31–62.
De Lahunta, A., Glass, E., and Kent, M. (2015). Veterinary Neuroanatomy and Clinical Neurology. St.
Louis: Elsevier.
Dewey, C.W. and Da Costa, R.C. (2016). Practical Guide to Canine and Feline Neurology. Hoboken:
Wiley‐Blackwell.
Dewey, C.W., Da Costa, R.C., and Thomas, W.B. (2016). Performing the neurologic examination. In:
Practical Guide to Canine and Feline Neurology, 3e (eds. C.W. Dewey and R.C. Da Costa), 92–137.
Hoboken: Wiley‐Blackwell.