Hypothyroid-associated neurologic signs in dogs - Veterinary Medicine
  • SEARCH:
Medicine Center
DVM Veterinary Medicine Featuring Information from:

ADVERTISEMENT

Hypothyroid-associated neurologic signs in dogs
Explore three cases of dogs with neurologic signs that were found to have hypothyroidism, and see when you should test for this disease in your patients with neuromuscular signs.


VETERINARY MEDICINE


Differential diagnoses

Based on the gait characteristics and decreased patellar and withdrawal reflexes, lack of menace response, and head tilt, a multifocal neuroanatomic diagnosis was made with likely involvement of the neuromuscular, visual, and vestibular systems, respectively. Differential diagnoses included ischemic infarction, inflammatory disease such as polymyositis, polyneuritis, immune-mediated disease such as myasthenia gravis, infectious diseases such as Toxoplasma or Neospora species infection, and neoplasia.

Initial diagnostic tests


Table 2: Case 1 CBC and serum chemistry profile abnormalities on preliminary examination
A complete blood count (CBC) and serum chemistry profile were performed (Table 2). The CBC disclosed a normocytic, normochromic anemia; mild thrombocytopenia; and lymphopenia. The serum chemistry panel revealed elevated aspartate transaminase (AST) and alkaline phosphatase (ALP) activities and a fasting hypercholesterolemia. The creatinine kinase activity was markedly elevated.

Administration of edrophonium hydrochloride did not result in clinical improvement. Because of the hypercholesterolemia, as well as the suspicion of infarction, pituitary-thyroid axis testing was performed (Table 2). The serum total thyroxine (T4) and free T4 concentrations were decreased, and the thyroid-stimulating hormone (TSH) concentration was increased. Since less than 5% of euthyroid-sick dogs will have an elevated TSH concentration, the results of thyroid testing in this dog were strongly consistent with primary hypothyroidism.2 Imaging of the brain to investigate the cause of the menace deficit and head tilt was not pursued based on the owner's financial constraints.

Despite the lack of improvement in strength after administration of edrophonium, titers for autoantibodies directed against the acetylcholine receptor (AchR) were assessed and found to be negative, excluding myasthenia gravis from consideration. Other causes for hypercholesterolemia such as diabetes mellitus, nephrotic syndrome, hyperadrenocorticism, and hypertriglyceridemia were not suspected in this patient because of a lack of relevant blood work abnormalities and clinical signs associated with these disease processes. Although primary hyperlipidemia was a differential diagnosis for this dog, a triglyceride concentration was not measured.

Treatment

Levothyroxine sodium was initiated (0.02 mg/kg orally twice daily). Within 24 hours, the head tilt and menace response deficit resolved, the postural reactions and reflexes improved, and the gait normalized. Based on thyroid hormone concentrations and TSH measurement combined with the rapid improvement after supplementation with T4, along with the exclusion of other etiologies to explain the multifocal neurologic deficits, neurologic and muscular dysfunction secondary to hypothyroidism was presumptively diagnosed. However, the self-limiting nature of ischemic lesions could have also accounted for the dog's rapid improvement.

The patient was discharged with instructions to return in two weeks for a recheck. The owners had traveled a long distance and did not want to return for the recheck visit, so personal communication at two weeks revealed that the patient's gait and strength were mildly improved. The advising clinician instructed the owners to return in seven to 10 days to have the patient reevaluated.


ADVERTISEMENT

Source: VETERINARY MEDICINE,
Click here