Page 798 - Small Animal Internal Medicine, 6th Edition

770 PART VI Endocrine Disorders

BOX 48.2
VetBooks.ir Clinical Manifestations of Hypothyroidism in the Adult Dog Exercise intolerance

Metabolic
Lethargy* Skeletal muscle wasting
Mental dullness* Knuckling
Inactivity* Ataxia
Weight gain* Circling
Cold intolerance Disorientation
Vestibular signs (head tilt, nystagmus)
Dermatologic Facial nerve paralysis
Endocrine alopecia* Trigeminal nerve paralysis
Symmetric or asymmetric Laryngeal paralysis (?)
“Rat tail” Seizures
Dry, brittle haircoat Myxedema coma
Hyperpigmentation Ocular
Seborrhea sicca or oleosa or dermatitis*
Pyoderma* Corneal lipid deposits
Otitis externa Corneal ulceration
Myxedema Uveitis

Reproductive Cardiovascular
Persistent anestrus Decreased contractility
Weak or silent estrus Bradycardia
Prolonged estrual bleeding Cardiac arrhythmias
Inappropriate galactorrhea or gynecomastia Gastrointestinal
Prolonged parturition
Stillbirth Esophageal hypomotility (?)
Periparturient puppy mortality Diarrhea
Testicular atrophy (?) Constipation
Loss of libido (?) Hematologic

Neuromuscular Anemia*
Hyperlipidemia*
Polyneuropathy Coagulopathy
Polymyopathy
Weakness* Behavior Abnormalities (?)

*Common.

mucopolysaccharides may accumulate in the dermis and bind and endoneurium, or after cerebral atherosclerosis, transient
water, causing the skin to thicken. Referred to as myxedema, ischemia or brain infarction, or the development of severe
this condition causes the skin to thicken predominantly in hyperlipidemia; they include seizures, ataxia, circling, weak-
the forehead and face of dogs, resulting in rounding of the ness, and proprioceptive and postural reaction deficits. These
temporal region of the forehead, puffiness and thickening of signs are often seen in conjunction with vestibular signs (e.g.,
the facial skin folds, and drooping of the upper eyelids. Myx- head tilt, nystagmus) or facial nerve paralysis. Peripheral
edema contributes to the classic “tragic facial expression” neuropathies identified in hypothyroid dogs include facial
sometimes observed in dogs with hypothyroidism. nerve paralysis, generalized weakness associated with diffuse
lower motor neuron tetraparesis, and knuckling or drag-
NEUROMUSCULAR SIGNS ging of the feet, with excessive wear of the dorsal part of the
Neuromuscular signs may be the predominant problem toenail. Hypothyroid myopathy is characterized by type II
in some dogs with hypothyroidism (see Box 48.2). Clini- myofiber atrophy, myofiber degeneration, and depletion in
cal signs may be multifocal, acute or chronic, and static or skeletal muscle carnitine, and may result in skeletal muscle
progressive. Other findings consistent with hypothyroidism wasting, weakness, exercise intolerance, and increased
may be absent. Hypothyroidism-induced segmental demy- serum of creatine kinase, aspartate aminotransferase, and
elination and axonopathy may cause signs referable to the lactate dehydrogenase activities. Thyroxine-responsive uni-
central or peripheral nervous system. Clinical signs refer- lateral forelimb lameness has also been observed in dogs. The
able to the central nervous system (CNS) may also appear relationship between hypothyroidism and laryngeal paraly-
after mucopolysaccharide accumulates in the perineurium sis or esophageal hypomotility remains controversial, in part