Neurological Manifestations of Hypothyroidism: A Retrospective Study of 29 Dogs

Abstract

Neuromuscular signs in association with hypothyroidism are described in 29 dogs. Eleven dogs had lower motor neuron signs, 9 had peripheral vestibular deficits, 4 had megaesophagus, and 5 had laryngeal paralysis. Primarily older (mean = 9.5 years), large-breed dogs were affected, and there was no sex or breed predisposition. Duration of clinical signs before presentation ranged from 2 to 8 weeks (mean = 5 weeks). The diagnosis was based on (1) results of neurological examination (29 dogs); (2) electromyographic abnormalities (1 8 dogs), including fibrillation potentials (n = 18). positive sharp waves (n = 15). and complex repetitive discharges (n = 4); (3) high serum cholesterol concentration (1 0 dogs: mean = 335 mg/dL); (4) low response to thyroid-stimulating hormone (29 dogs; mean T4 prestimulation concentration = 0.8 ag/dL; mean T4 poststimulation = 1.2 pg/dL); and (5) good response to thyroxine supplementation (26 dogs). Dogs with vestibular deficits had abnormal brainstem auditory-evoked responses (BAER), including increased latencies of P, -P6 and decreased amplitude of P4,5-N5. Seven other dogs had similar BAER abnormalities without manifesting clinical rimary hypothyroidism'-' is a relatively common endo-

Neurologic Dysfunction in Hypothyroid, Hyperlipidemic Labrador Retrievers

“…Unilateral vestibular disease and facial nerve paralysis have been reported previously in hypothyroid dogs. 1,2,5 These peripheral nerve signs may arise from abnormal axonal transport and demyelination caused by Schwann cell dysfunction. 1,5,6 However, a generalized peripheral neuropathy would seem more likely, as is observed in diabetes mellitus, insulinomas, and the generalized lower motor neuron signs reported previously in dogs with hypothyroidism.…”

“…The normally functioning thyroid gland supports metabolism and consequently normal axonal function and transport, which alone may explain at least some neurologic dysfunction in hypothyroid patients. 4,5,13 In fact, slow axonal transport was decreased in hypothyroid rats. 14 In patients with polyneuropathy secondary to hypothyroidism, axonal degeneration, demyelination, mitochondrial glycogen deposition in axons and Schwann cells, and possibly Schwann cell dysfunction have been reported.…”

“…10 Cranial neuropathies reported in dogs include facial paralysis, peripheral vestibular disease, trigeminal dysfunction, laryngeal paralysis, and megaesophagus. 2,5,6 CNS signs reported include seizures, coma, and brainstem signs. 2,[7][8][9]11 In addition, generalized neuromuscular disease and unilateral forelimb lameness have been associated with hypothyroidism.…”

“…2,[7][8][9]11 In addition, generalized neuromuscular disease and unilateral forelimb lameness have been associated with hypothyroidism. [3][4][5] Despite many reports, establishing a causal relationship between these neurologic manifestations and hypothyroidism has been difficult. Some of the clinical signs, such as those referable to the peripheral vestibular system and facial nerve, frequently present as idiopathic conditions in dogs that tend to resolve on their own, making it difficult to prove an association with hypothyroidism by response to therapy.…”

“…[1][2][3][4][5][6][7][8][9] A range of neurologic manifestations has been reported, including cranial neuropathies, central nervous system (CNS) signs, and generalized peripheral neuropathies. Of these, peripheral neuropathies are reported with greatest frequency.…”