When compulsive licking hides thyroid failure: a case of hypothyroidism with behavioral signs in a Jack Russell Terrier

Abstract

Primary hypothyroidism is a common endocrine disorder in dogs that often manifests with classic metabolic and dermatological signs. However, behavioral manifestations can occur as primary or dominant clinical signs, leading to potential diagnostic challenges. This case report describes a 7-year-old castrated male Jack Russell Terrier referred for bilateral compulsive forelimb licking, social isolation, and behavioral rigidity following a change in the family system, which acted as an emotional stressor. Physical examination and routine laboratory tests revealed elevated triglycerides and hypercholesterolemia, mild normocytic normochromic anemia and hypoalbuminemia while thyroid function tests requested by the behaviorist as a diagnostic workup to frame compulsive behavior confirmed primary hypothyroidism (fT4 <3.86 pmol/L, tT4 <0.50 µg/dL, TSH 5.14 ng/mL). The signs presented have been hypothesized as an anxiety disorder secondary to endocrinopathy, with a dysregulation of multiple fundamental affective systems rather than as a set of psychiatric disorders. Treatment with sodium levothyroxine alongside a behavioral modification protocol led to biochemical normalization, complete resolution of compulsive licking, and full restoration of emotional balance within 32 weeks. This case suggests the importance of comprehensive endocrine screening in veterinary behavioral medicine when presenting signs, including sudden emotional dysregulation and compulsive behaviors.