[Reevaluation of validity of percent creatinuria for diagnosing steroid myopathy]

Steroid myopathy is usually a slowly progressive disease, which causes weakness primarily to the proximal muscles of the upper and lower extremities. The monitoring of this problem is difficult in situations in which the primary disease itself produces muscle weakness. The distinguishing feature in steroid myopathy is the occurrence of creatinuria in the presence of normal muscle enzymes including creatine kinase and aldolase. To evaluate the usefulness of percent creatinuria {urinary excretion of creatine/(urinary excretion of creatine + urinary excretion of creatinine)} in the diagnosis of steroid myopathy, we measured percent creatinuria in 26 patients (14 male and 12 female) without muscle diseases before the initiation of steroid treatment We found that the median values of percent creatinuria of the male and female patients were 2.5% and 17.1%, and that the ratios of the male and female patients presenting with an elevated percent creatinuria (more than 10%) were 3 out of 14 patients (21.4%) and 8 out of 12 patients (66.7%), respectively. We also found one patient with mild renal dysfunction presenting with an elevated percent creatinuria but without muscle weakness or myalgia. These findings suggest that the measurement of percent creatinuria is of little value in the diagnosis of steroid myopathy with a cutoff value of 10%. Furthermore, it is important to measure percent creatinuria before the steroid treatment, while paying close attention to the measurement method, sex, renal function and protein level of the diet.