Neurological signs (NS) can occur in canine hypothyroidism and sometimes, they are the unique manifestation of this disease. The objective of the present retrospective study was to evaluate the frequency of NS, including seizures, among hypothyroid dogs at diagnosis. Fifty-nine dogs newly diagnosed with hypothyroidism at The Veterinary Teaching Hospital Complutense Madrid between October 2011 and March 2017 were reviewed.

Age ranged between 2.3 and 6.5 years, 24/59 females, 37/59 males, 29/59 intact and 30/59 neutered. Duration of clinical signs before diagnosis ranged from 1 to 24 months (mean 9±6.7 months). Clinical signs, body condition score (BCS), concurrent diseases, body weight, total-thyroxine (tT₄) ,free-thyroxine (fT₄), thyroid stimulating hormone (TSH) and cholesterol levels were recorded.

Neurological signs were present in 17/59 dogs (29%), being seizures the most common (13/17), while 4/17 dogs presented other NS (vestibular deficits, megaesophagus, head bobbing syndrome and peripheral neuropathies).

No association was observed between seizures and age, sex, BCS, duration of signs before diagnoses, tT₄ and fT₄ levels, reproductive status or other NS.

Mean plasma TSH in dogs without seizures (2.0±1.7 ng/ml) was significantly higher than in dogs without this NS (1.3±2.2 ng/ml) (p=0.04). Among the 13 dogs that presented seizures, 7/13 (54%) had normocholesterolemia and 6/13 (46%) hypercholesterolemia; including one dog (8%) with plasma cholesterol levels above 620 mg/dl. However, in the group of dogs without seizures, only 4/29 (14%) presented normal cholesterol levels and 25/29 (85%) hypercholesterolemia, including 12/29 (41%) with plasma cholesterol levels above 620 mg/dl of (p=0.01)

Prevalence of seizures at diagnosis was higher in dogs with clinical evidence of myxoedema (4/9; 44%) compared with dogs without this clinical sign (9/50; 18%) (p=0.078)

Neurological signs have been described to occur in 7.5% of hypothyroid dogs. However, in the present study, 29% of hypothyroid dogs had NS, and among them, 76.5% presented seizures. Probably, our diagnostic protocol used for convulsive patients, were thyroid hormones testing is always included before anticonvulsive treatment is administered, is related with this finding. Different mechanisms have been proposed to explain the development of NS in hypothyroid dogs, including alterations in axonal transport and ischemia. Hypercholesterolemia and atherosclerosis and consequent hypoxia of central nervous system has been observed and proposed as a cause of NS; however, in the present study hypercholesterolemia is definitely not related to seizures. Clinical evidence of myxoedema though seems to be related with seizures.

Disclosures

No disclosures to report.