Goitrous hypothyroidism associated with treatment with trimethoprim-sulfamethoxazole in a young dog.
METHODS
A 16-week-old female Boxer that had been treated for 5 weeks with trimethoprim-sulfamethoxazole and chloramphenicol because of aspiration pneumonia was evaluated for bilaterally symmetric masses in the subcutaneous tissues of the ventral neck, in the region of the larynx.


RESULTS
Fine-needle aspirates were obtained from the neck masses; cytologic examination revealed well-differentiated thyroid epithelial tissue. A blood sample was collected for serum biochemical and thyroid function analyses. Mild hyperphosphatemia, severe hypercholesterolemia, mild hyperkalemia, and a mild increase in creatine kinase activity were identified. Serum concentration of total thyroxine was less than the lower reference limit, and that of thyroid-stimulating hormone was greater than the upper reference limit. Findings were consistent with a diagnosis of clinical hypothyroidism in a skeletally immature dog.


RESULTS
Treatment with trimethoprim-sulfamethoxazole was discontinued. The dog was reevaluated 3 weeks later, at which time the neck masses were markedly decreased in size. Serum concentrations of cholesterol and potassium were lower; serum concentrations of total thyroxine and thyroid-stimulating hormone were near or within respective reference ranges. Age-appropriate increases in serum phosphorus concentration and serum alkaline phosphatase activity were also detected.


CONCLUSIONS
To the authors' knowledge, this is the first report of antimicrobial-induced goiter in a dog. Cytologic examination of fine-needle aspirates and interpretation of data from serum biochemical and thyroid function analyses were needed to obtain a definitive diagnosis. Practitioners should include goiter among the differential diagnoses for ventral neck swellings in young dogs receiving potentiated sulfonamide antimicrobials.
Seelig
Davis M
DM
Department of Microbiology, Immunology, and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.
Whittemore
Jacqueline C
JC
Lappin
Michael R
MR
Myers
Alan M
AM
Avery
Paul R
PR
D000818:Animals; D000890:Anti-Infective Agents / Q000009:adverse effects* / Q000627:therapeutic use; D004283:Dog Diseases / Q000097:blood / Q000139:chemically induced*; D004285:Dogs; D005260:Female; D007037:Hypothyroidism / Q000097:blood / Q000139:chemically induced / Q000662:veterinary*; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism; D013963:Thyroid Hormones / Q000097:blood; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000009:adverse effects* / Q000627:therapeutic use
D000890:Anti-Infective Agents; D013963:Thyroid Hormones; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D013972:Thyrotropin; D013974:Thyroxine