Please consider the following comments as general in nature as I am not privy to all the details of the case.
I would think it is very unusual to have crescentic disease regress so quickly. He may also have had ATN along with the glomerulonephritis which improved, explaining the rapid recovery in renal function. Did his biopsy show ATN? While he may have clinically improved, he could still have crescents on a repeat renal biopsy.
Combined immunotherapy has been used in IgA nephropathy and is reserved for patients with severe disease. With over 50% crescents, this patient would definitely be classified as having more severe disease. However, there are limited data evaluating combination therapy for IgA nephropathy. There is a small trial [link below] in 12 patients patients with crescentic IgA using cyclophosphamide in addition to prednisone showing regression of proteinuria and histologic findings with stabilized renal function compared to historically matched controls. In your patient's case however, his renal function has already improved prior to treatment.
At this point, as it is quite early (1 week post presentation), and before committing any patient to any additional combined therapy, one might consider observing the clinical response to the prednisone (and ACE or ARB). Studies of patients with severe disease had progressively worsening renal function with high-grade proteinuria. In this case, the clinical parameters are improving and treatment has been added to further suppress the disease.
Dr. Jordan Weisntein