Concurrent Kidney Disease
Both hyperthyroidism and chronic kidney disease (CKD) are common diseases of geriatric cats which can occur at the same time as one another.
The diagnosis of hyperthyroidism in a cat with CKD can be complicated because non-thyroidal illnesses such as CKD can suppress plasma total thyroxine concentrations into the normal range even when hyperthyroidism is present.
Hyperthyroidism can also complicate the diagnosis of concurrent CKD as hyperthyroidism causes an increase in the glomerular filtration rate and a reduction in body muscle mass, which both lead to a reduced plasma creatinine concentration. This can mask the presence of underlying CKD, as we use plasma creatinine concentration as a measure of renal function.
Despite this, studies show that around 10% of hyperthyroid cats will be azotemic at the time of diagnosis of hyperthyroidism and these patients have a worse prognosis than hyperthyroid cats that are non-azotaemic at the time of diagnosis (Williams et al, 2010).
For cats that are non-azotaemic at diagnosis, but subsequently develop azotaemia (IRIS stage 2 or 3) after treatment of disease, there is currently no indication to undertreat hyperthyroidism in these patients (Williams et al, 2010). However, iatrogenic hypothyroidism
Further details on the research behind the treatment of cats with concurrent hyperthyroidism and chronic kidney disease can be found within our dedicated E-learning module accessed here