Current views on epidemiology of renal tuberculosis

The epidemiology of renal tuberculosis is characterised by a considerable variation in the frequency and distribution of the infection. It is difficult to be sure of the prevalence of renal tuberculosis (RTB throughout the world since survey results are to a certain extent dependent on the technique used. While the diagnosis of this disease is difficult, a high index of suspicion at all times with combined investigative tools permit the accurate diagnosis of most cases. Prevalence rates of over 5% in the general population have been reported in the Western countries. RTB is the commonest form of extrapulmonary tuberculosis among the Caucasians with male preponderance. There is paucity of data on the prevalence of RTB in tropical developing countries because of the general impression that this form of tuberculosis is rare in Blacks. However, hospital based retrospective data on extrapulmonary tuberculosis in Nigeria have revealed RTB prevalence rates of 1-3%. Tuberculosis involving the lymph nodes have been observed to be the commonest form of extrapulmonary tuberculosis in Nigeria. The age distribution of RTB obtained from different studies ranged from 14 to 70 years with the majority being below 50 years of age. Various male to female ratios ranging from 1:1 to 3:1 have been reported from different studies. Renal involvement in tuberculosis occurs through haemogeneous spread from a primary focus and is usually a bilateral disease. The most common primary site are the lungs. Many studies on pulmonary tuberculosis (PTB) outside Nigeria have shown that 26-75% of RTB co-exist with active PTB and 6-10% of screened open PTB patients have renal involvement. A recent study on RTB among active PTB patients in Ilorin, Nigeria revealed prevalence rate of 9.5% by urine Z-N positivity and 14% by utilising a combination of urine Z-N stain, sterile pyuria and renal tissue histology. It should be clear from the foregoing that RTB is not uncommon in both Caucasians and Blacks. It may be commoner in tropical developing countries than the Western World since PTB which is the main primary focus is endemic in these areas.