Effects on the skin
Through their inhibitory effects on keratinocyte and fibroblast proliferation, as well as on collagen synthesis, glucocorticoids
can cause marked atrophy of the skin. With glucocorticoid use in people, epidermal lipids decrease and transepidermal water
loss increases, both of which can lead to adverse effects such as scaling, hair loss, follicular atrophy, bruising, and thinning
of the skin.34 These signs appear infrequently in cats receiving commonly used glucocorticoid-dosing protocols, although higher doses and
longer treatment courses can cause similar signs.24
Table 2. Reported Cutaneous Signs in 18 Cats with Iatrogenic Hyperadrenocorticism*
Table 2 shows the cutaneous abnormalities seen in 18 cats with iatrogenic hyperadrenocorticism. In some of these cats, it is unclear
whether glucocorticoids or the primary cutaneous conditions that were being treated were responsible for the observed signs.
The glucocorticoid-induced cutaneous atrophy in cats can be extremely severe, leading to paper-thin skin that may tear either
spontaneously or with only gentle manipulation (Figure 2).18,24 Curling of the pinna is another unique, but rare, adverse effect of glucocorticoid use in cats (Figure 3).15,24
Figure 2. Marked cutaneous atrophy and fragility leading to tearing of the skin in a cat.
Effects on the cardiovascular system
Several recent studies have documented cardiovascular risks associated with glucocorticoid use in cats. In two recent cases,
a series of temporal associations were seen between glucocorticoid administration and the development of congestive heart
failure in cats without pre-existing cardiac disease.35,36 The most common glucocorticoid associated with this adverse effect was methylprednisolone acetate; signs were seen as quickly
as one day following administration.36 Congestive heart failure in affected cats was associated with hypertrophic cardiomyopathy; however, in cats that survived
the initial crisis, the hypertrophic changes were observed to resolve in time after withdrawal of glucocorticoids.35,36 These cats had longer survival times compared with cats that had congestive heart failure caused by other forms of disease,
leading the authors to propose that cats may develop a unique form of glucocorticoid-associated congestive heart failure.36 A follow-up study on the pathogenesis of this adverse effect suggested that plasma volume expansion caused by the hyperosmotic
effect of glucocorticoid-induced hyperglycemia was responsible.37
Figure 3. Curling of the pinna secondary to chronic glucocorticoid use in a cat.
Cats exhibit several important differences from other species in their response to glucocorticoid therapy. I hope that knowledge
of these species differences will enable practitioners to tailor the most effective and safe treatment plan for their feline
patients. While cats typically tolerate glucocorticoids well, clinicians should be aware of, and monitor for, potentially
serious adverse effects, such as diabetes mellitus, fragile skin, and congestive heart failure.
Andrew Lowe, DVM, MSc, DACVD
Fox Valley Animal Referral Center
Appleton, WI 54169