Primary Hypothyroidism and Thyroid Goiter in an Adult Cat

A 5-year-old neutered male domestic shorthair cat was diagnosed with primary hypothyroidism and thyroid goiter, presenting with lethargy, weight gain, and an unkempt hair coat. Diagnostic tests confirmed low free thyroxine (fT4) and high thyroid-stimulating hormone (TSH) levels. Treatment with levothyroxine led to significant clinical improvement, normalization of fT4 levels, and resolution of skin lesions, although TSH levels remained elevated. The cat remained in good health 8 months post-diagnosis. The case highlighted the importance of considering hypothyroidism in cats with similar symptoms and demonstrated the effectiveness of hormone replacement therapy. Potential causes included dietary iodine imbalance, chronic exposure to thyrotoxic substances, or congenital hypothyroidism manifesting later in life.