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J Vet Intern Med. 2010 Jul-Aug;24(4):875-81. doi: 10.1111/j.1939-1676.2010.0515.x. Epub 2010 Apr 16.

Resistance of the peripheral nervous system to the effects of chronic canine hypothyroidism.

Author information

1
Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060, USA. jrossmei@vt.edu

Abstract

BACKGROUND:

Hypothyroidism has been implicated in the development of multiple peripheral mono- and polyneuropathies in dogs. The objectives of this study were to evaluate the clinical and electrophysiologic effects of experimentally induced hypothyroidism on the peripheral nervous system of dogs.

HYPOTHESIS:

Chronic hypothyroidism will induce peripheral nerve sensorimotor dysfunction.

ANIMALS:

Eighteen purpose-bred, female dogs.

METHODS:

Prospective, longitudinal study: Hypothyroidism was induced by radioactive iodine administration in 9 dogs, and the remaining 9 served as untreated controls. Neurological examinations were performed monthly. Electrophysiologic testing consisting of electromyography (EMG); motor nerve conduction studies of the sciatic-tibial, radial, ulnar, and recurrent laryngeal nerves; sciatic-tibial and ulnar F-wave studies; sensory nerve conduction studies of the tibial, ulnar, and radial nerves; and evaluation of blink reflex and facial responses were performed before and 6, 12, and 18 months after induction of hypothyroidism and compared with controls.

RESULTS:

Clinical evidence of peripheral nervous dysfunction did not occur in any dog. At 6 month and subsequent evaluations, all hypothyroid dogs had EMG and histologic evidence of hypothyroid myopathy. Hypothyroid dogs had significant (P<or=.04) decreases in ulnar and sciatic-tibial compound muscle action potentials over time, which were attributed to the concurrent myopathy. No significant differences between control and hypothyroid dogs were detected in electrophysiologic tests of motor (P>or=.1) or sensory nerve conduction velocity (P>or=.24) or nerve roots (P>or=.16) throughout the study period, with values remaining within reference ranges in all dogs.

CONCLUSION:

Chronic hypothyroidism induced by thyroid irradiation does not result in clinical or electrophysiologic evidence of peripheral neuropathy, but does cause subclinical myopathy.

PMID:
20412437
DOI:
10.1111/j.1939-1676.2010.0515.x
[Indexed for MEDLINE]
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