You are asked to examine an 18-year-old Warmblood gelding that has developed progressive alopecia, which started in the neck region. Haematological evaluation reveals a haematocrit of 30% (n = 36–42%) and a normal leucocyte count (8.9x109/l with 21% lymphocytes, 1% eosinophils and 78% neutrophils). The total serum protein concentration is normal (81g/l with 31.7% albumin, 14.3% alpha-globulins, 29.4% beta-globulins and 24.6% gamma-globulins). Basal T4 concentration is low.
What is the most likely endocrinopathy to cause these lesions?
Hypothyroidism. Thyroid dysfunction is rare in the horse. Equine hypothyroidism can be classified into four groups:
hypothyroidism in foals;
hypothyroidism in adult horses;
euthyroid sick syndrome; and
Hypothyroidism in foals is usually associated with prognathism, ruptured tendons, forelimb contracture, delayed ossification of the carpal and tarsal bones, and goitre. The prognosis is extremely poor.
The clinical signs of hypothyroidism in adult horses are cessation of growth, hypothermia, lethargy, irregular areas of alopecia and thickened face.