Renal Tuberculosis

Renal tuberculosis is infection of the kidney and urinary tract by Mycobacterium tuberculosis, usually from haematogenous spread during primary infection, with reactivation 5 to 40 years later.

• It is the commonest form of genitourinary tuberculosis and accounts for 2 to 20 percent of extrapulmonary tuberculosis; frequent in Kenya because of high tuberculosis and HIV burden.
• Bacilli lodge in the renal cortex, then spread to the medulla, papillae, ureter, bladder, prostate and epididymis.
• Risk factors: HIV, diabetes, immunosuppression, malnutrition, renal failure, silicosis, previous tuberculosis, close contact.

Insidious: frequency, dysuria, nocturia, haematuria, flank pain, sterile pyuria (acid urine with persistent pyuria and negative routine culture), low grade fever, night sweats, weight loss; many are asymptomatic until late.

• Other findings: epididymal nodularity or thickened vas deferens, prostatitis, scrotal sinuses, hypertension, small contracted bladder.
• Differential diagnosis: recurrent urinary tract infection, urolithiasis, urothelial malignancy, schistosomiasis, chronic pyelonephritis, interstitial cystitis, papillary necrosis, renal cell carcinoma, xanthogranulomatous pyelonephritis.
• Complications: ureteric strictures with hydronephrosis, calyceal destruction, autonephrectomy ("putty kidney"), renal failure, contracted bladder, vesicoureteric reflux, urethral stricture, fistulae, hypertension, infertility, secondary bacterial infection.

Three to six early morning urine samples for acid fast smear and culture (Löwenstein-Jensen or liquid media), plus rapid molecular testing (Xpert MTB/RIF on urine) with rifampicin resistance detection; urinalysis shows sterile pyuria and haematuria.

• Blood tests: creatinine, electrolytes, full blood count, ESR, HIV, glucose; chest radiograph (abnormal in about half); tuberculin test or interferon gamma release assay are supportive only.
• Imaging: ultrasound (hydronephrosis, calcification, scarring); CT urography or intravenous urography (calyceal erosion, "moth-eaten" calyces, papillary necrosis, infundibular strictures, hydrocalycosis, ureteric beading and strictures, calcification, non-functioning kidney, small bladder).
• Cystoscopy with biopsy for bladder lesions; histology shows caseating granulomas.
• Screen for coinfection and drug resistance.

Supportive: nutrition, treat HIV and diabetes, avoid nephrotoxins, relieve obstruction.

Pharmacological (drug susceptible disease, 6 months total):

• Intensive phase for 2 months: rifampicin 10 mg/kg (450 mg if below 50 kg, 600 mg if 50 kg or more) once daily, isoniazid 5 mg/kg (300 mg) once daily, pyrazinamide 25 mg/kg (1.5 g if below 50 kg, 2 g if 50 kg or more) once daily, ethambutol 15 mg/kg once daily (fixed dose combinations, taken 30 to 60 minutes before food).
• Continuation phase for 4 months: rifampicin plus isoniazid; extend to 9 to 12 months in complicated or slow-responding disease.
• Pyridoxine 25 to 50 mg daily with isoniazid.
• Renal impairment (creatinine clearance below 30 mL/min): rifampicin and isoniazid unchanged, pyrazinamide 25 mg/kg and ethambutol 15 mg/kg three times weekly after dialysis on dialysis days.
• Children: rifampicin 15 mg/kg, isoniazid 10 mg/kg, pyrazinamide 35 mg/kg, ethambutol 20 mg/kg daily.
• Prednisolone 40 mg daily tapered over 6 to 8 weeks to reduce stricture formation in ureteric or bladder involvement (selected cases, with tuberculosis therapy).
• HIV coinfection: antiretroviral therapy within 2 weeks if CD4 is below 50 cells/mm3, otherwise within 8 weeks; watch immune reconstitution syndrome; dolutegravir 50 mg twice daily with rifampicin.
• Drug resistance: second line regimens chosen by susceptibility results.
• Monitor liver function monthly initially; stop for ALT above 5 times normal or above 3 times with symptoms.

Procedures

• Ureteric stent or percutaneous nephrostomy for obstruction (at the start of treatment, to preserve function); stricture dilation or reconstruction after 4 to 6 weeks of treatment.
• Nephrectomy for non-functioning calcified kidney with uncontrolled infection, intractable pain, hypertension or suspicion of tumour; partial nephrectomy for localised destruction.
• Augmentation cystoplasty for contracted bladder.

Special groups: HIV (specialist care), pregnancy (usual drugs, rifampicin, isoniazid, ethambutol with pyridoxine; avoid streptomycin), children, transplant recipients.

Red flags: obstruction with infection, rising creatinine, hypertension, no response at 2 months, haematuria with weight loss.

Follow-up: urine culture and imaging at 2 months, at the end of treatment and at 6 and 12 months; annual ultrasound for 3 to 5 years; creatinine and blood pressure.