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Geriatric HIMS in Dogs: A Practical Look at a Cushing’s-Like Syndrome We May Be Missing
Dr. Keith A Hnilica, DVM, MS, DACVD
Apr 16, 2026
6 min read
Geriatric HIMS—short for Hormone Imbalance with Melatonin Sensitivity—is best viewed as a proposed clinical syndrome, not yet a formally established veterinary diagnosis. The idea fits a familiar pattern in older, usually small-breed dogs: they start to look and act “old before their time,” showing potbelly change, increased drinking and urination, coat thinning, recurrent skin or urinary infections, reduced vitality, and a general Cushing’s-like appearance, yet standard testing may not cleanly confirm classic hyperadrenocorticism. In veterinary endocrinology, this overlap is closest to what has been called atypical hyperadrenocorticism, where dogs show compatible signs but have normal routine cortisol testing and may instead have abnormalities in other adrenal steroid pathways.
That is where the HIMS concept becomes interesting. Published veterinary sources have described melatonin as a treatment used in dogs with atypical Cushing’s patterns, especially when sex-hormone or intermediate steroid abnormalities are suspected. Melatonin has been discussed as having anti-gonadotropic effects and influence on steroid metabolism, including effects related to estradiol pathways. Older work in dogs also found measurable changes in sex-hormone concentrations after melatonin administration.
So the practical value of “geriatric HIMS” is this: it gives clinicians a useful way to think about a subset of older dogs that appear metabolically off, inflamed, fragile, infection-prone, and prematurely aged, even when the standard workup does not fully explain the patient. It may help frame a dog whose endocrine imbalance is broader than cortisol alone. Still, the evidence base is not yet strong enough to say HIMS is a validated disease entity. The safer conclusion is that it is a thought-provoking clinical model that overlaps with atypical hyperadrenocorticism and deserves prospective study, especially in dogs that seem to improve with melatonin-based support.