A woman with deteriorating renal function

A 46 year old woman with diabetes, hypertension and bronchial asthma was admitted with signs of a respiratory infection and bilateral pedal edema. She was treated appropriately with antibiotics, diuretics and her usual medicines for diabetes, hypertension and asthma. Her ECG was normal.  Her renal function was impaired and she had a serum creatinine of 135umol/L. Her 24 hour urine protein estimation showed a value of 5.52grams protein. A diagnosis of diabetic nephropathy with renal impairment was made and treatment with Enalapril 10mg BD was initiated. One month later, she was asymptomatic even though she still had pedal edema. At this time her serum creatinine was 140umol/L.

Two months later her serum creatinine was 129umol/L. At this time the dose of Enalapril was increased to 20mg BD because her blood pressure was higher than the target value of 130/80mm Hg. A month later her serum creatinine was 150umol/L and Tab Telmisartan 80mg OD was added to her existing medication because the blood pressure was still above target value. When reviewed three months later, her blood pressure was normal but her serum creatinine was 178umol/L. At this point the Telmisartan was discontinued but, even after that, her serum creatinine continued to increase and touched a value of 222umol/L two months later. Seeing this, her doctors decided to stop Enalapril also and to treat her hypertension without any ACE inhibitors or angiotensin receptor blockers.

Slowly, within the next six months, her serum creatinine decreased and it returned to her earlier baseline value 135umol/L.


Discussion

In view of her deteriorating renal function after angiotensin inhibition, can this woman be considered to have renovascular hypertension?
No, I do not think she has renal artery narrowing because her renal function did not deteriorate even with high doses of Enalapril. 

Then what was the cause of her serum creatinine touching a value of 222umol/L?
I believe that this rapid deterioration in renal function was due to the combination of  Enalapril and Telmisartan. A high dose of Telmisartan was added soon after the dose of Enalapril had been doubled. Rapid angiotensin inhibition can lead to deterioration in renal function. 

Can this patient be started again on Enalapril now?
Yes, she can. It is in her best interests to introduce an ACE inhibitor again because of the renal protection it offers. But the medication must be started in a low dose and dose increases must only be done gradually.


How much of an increase in serum creatinine is allowed after introducing an ACE inhibitor or an angiotensin receptor blocker?
An increase of up to 30 percent from the baseline is permissible. This acute increase in serum creatinine does reflect impaired glomerular filtration but it may reverse over time. The long term benefit of angiotensin inhibition outweighs the slight, and often short-term, acute renal dysfunction. 

What is the likely cause of her pedal edema?
From the available information, nephrotic syndrome has to be considered as the most likely cause of her edema.