Retrospective Evaluation of Gastrointestinal Signs in Hypothyroid Dogs

SIMPLE SUMMARY: Gastrointestinal signs are reported in humans with hypothyroidism, and resolution of GI signs was reported with thyroid hormone supplementation; however, GI involvement in the clinical presentation of dogs with hypothyroidism has not been investigated over the past decades. Our study aimed to fill this scientific gap, evaluating the prevalence and characteristics of concurrent gastrointestinal signs in hypothyroid dogs, describing laboratory and ultrasonographic findings and analyzing gastrointestinal signs after thyroid replacement therapy. Approximately 45% of hypothyroid dogs had gastrointestinal signs, especially constipation and diarrhea. At the abdominal ultrasound, gallbladder disease was present in more hypothyroid than euthyroid dogs. Finally, all hypothyroid dogs had a significant improvement in gastrointestinal signs after thyroid therapy. Our results, especially the improvement in clinical intestinal signs following thyroid therapy, support the association between gastrointestinal signs and hypothyroidism. ABSTRACT: Few observations about gastrointestinal (GI) signs in hypothyroid dogs (hypo-T dogs) are available. We aimed to evaluate the prevalence and characteristics of concurrent GI signs in hypo-T dogs, describe clinicopathological, hepato-intestinal ultrasound findings in hypo-T dogs, investigate changes in GI signs after thyroid replacement therapy (THRT). Medical records of suspected hypo-T dogs from two hospitals were retrospectively reviewed. The inclusion criteria were: (1) having symptoms and clinicopathological abnormalities related to hypothyroidism (i.e., mild anemia, hyperlipemia); (2) not being affected by systemic acute disease; (3) not having received any treatment affecting thyroid axis. Hypothyroidism had to be confirmed using low fT4 or TT4 with high TSH and/or inadequate TSH-stimulation test response; otherwise, dogs were assigned to a euthyroid group. Clinical history, GI signs, hematobiochemical parameters, and abdominal ultrasound findings were recorded. Hypo-T dogs were assigned to the GI group (at least 2 GI signs) and not-GI group (1 or no GI signs). Follow-up information 3–5 weeks after THRT was recorded. In total, 110 medical records were screened: 31 dogs were hypo-T, and 79 were euthyroid. Hypo-T dogs showed a higher prevalence of GI signs (44%), especially constipation and diarrhea (p = 0.03 and p = 0.001), than euthyroid dogs (24%) (p = 0.04). Among hypo-T dogs, no difference in hematological parameters between GI and non-GI groups was found. Hypo-T dogs had a higher prevalence of gallbladder alterations than euthyroid dogs (20/25; 80% and 32/61; 52% p = 0.04). The hypo-T GI group showed a significant improvement in the GI signs after THRT (p < 0.0001). Specific investigation for concurrent GI diseases in hypo-T dogs was lacking; however, improvement in GI signs following THRT supports this association between GI signs and hypothyroidism.