Peer-reviewed veterinary case report
Cat developed hypothyroidism after sulfa antibiotic for nocardiosis
By Alexander, Deborah et al.·Published in Journal of veterinary internal medicine·2025·Vida Felina Veterinary Clinic, Brazil·View original on PubMed →
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Original publication title: Iatrogenic Primary Hypothyroidism Associated With Sulfamethoxazole-Trimethoprim Treatment of Nocardiosis in a Cat.
- Species:
- cat
Plain-English summary
A 9-year-old mixed breed cat with a history of skin problems was diagnosed with nocardiosis, a type of bacterial infection. After starting treatment with a medication called trimethoprim-sulfa, the cat developed symptoms of hypothyroidism, including an enlarged thyroid and low thyroid hormone levels. Once the medication was stopped, the cat's thyroid levels returned to normal, confirming that the medication caused the thyroid issue. The cat also had a skin lesion that was surgically removed and identified as being caused by the same bacteria.
People also search for: cat skin lesions treatment · cat hypothyroidism symptoms · trimethoprim sulfa side effects in cats
Abstract
A 9-year-old mixed breed cat with a history of recurrent ulcerated skin lesions was diagnosed with nocardiosis. Three months after initiating potentiated sulfonamide treatment, the cat developed goitrous hypothyroidism, characterized by palpable enlargement of both thyroid lobes, low serum concentrations of total thyroxine (T4) and free thyroxine (fT4), and high serum thyroid-stimulating hormone (TSH) concentration. Thyroid scintigraphy identified symmetrical enlargement of both thyroid lobes, with increased radionuclide (Tc-pertechnetate) uptake. Upon discontinuation of trimethoprim-sulfa, serum concentrations of T4, fT4, and TSH returned to normal, confirming the diagnosis of iatrogenic, drug-induced thyroid dyshormonogenesis leading to hypothyroidism. A skin lesion was surgically removed, and microscopy disclosed branched filaments along with characteristic Gram-positive coccobacilli and Splendore-Hoeppli phenomenon. Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), the clinical isolate was identified as Nocardia puris.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/40072270/