Adult-onset demodicosis: looking for the underlying cause
9-year-old crossbred dog with no previous skin problems, presenting multifocal alopecia, erythema, comedones and scaling on the face, trunk and limbs. Deep skin scrapings show numerous adult Demodex canis, nymphs and eggs.
Besides starting acaricidal treatment, what is most appropriate?
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A. Reassure the owner: it is the same form seen in puppies and usually resolves on its own
Spontaneous remission is typical of localised juvenile demodicosis. Generalised adult-onset disease rarely resolves without treatment and almost always has a predisposing factor.
B. Add anti-inflammatory prednisolone to control the erythema
Glucocorticoids depress immunity against the mite and worsen demodicosis; moreover, glucocorticoid excess is one of its most common causes in adult dogs.
C. Measure total T4 now and, if low, diagnose hypothyroidism
Generalised demodicosis with pyoderma is a concurrent illness that lowers T4 without true hypothyroidism. Interpret it alongside TSH and the clinical picture, or repeat it once the skin is controlled.
D. Investigate immunosuppression: drugs, hypercortisolism, hypothyroidism, neoplasia and leishmaniosis
Correct. In adult dogs demodicosis is usually a marker of underlying disease. Review medication (glucocorticoids, chemotherapy, oclacitinib) and run haematology, biochemistry, urinalysis, endocrine tests as indicated, Leishmania serology and imaging if appropriate.
lightbulb Key takeaway
Demodicosis appearing for the first time in an adult dog demands a search for the cause: hypercortisolism (spontaneous or iatrogenic) and hypothyroidism are the most associated endocrine diseases, and in Spain do not forget leishmaniosis. Isoxazolines are highly effective, but relapses are common if the cause is not corrected; continue treatment until repeated scrapings are negative.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.