Q. A fit and well 60-year-old male is referred by his GP for an opinion on an asymptomatic 5 mm lower pole renal stone found incidentally on a CT scan. How common are asymptomatic renal stones and are they safe to monitor?
A. Historically the prevalence of asymptomatic renal stones was estimated to be between 3% and 5% within the United Kingdom [16]. ttere is now clear evidence that stone disease is increasing across all Western societies. Stamatelou et al. showed an increase in prevalence from 3.6% to 5.2% between 1976 and 1994 in a U.S.-based survey of over 15,000 patients [17]. An even higher prevalence of 7.8% (n = 395) was reported in a more objective study of 5,047 U.S. patients who underwent CT colonography screening between 2004 and 2008 (men 9.7% versus women 6.3%) with mean stone size of 3 mm and an average of two stones per patient [18]. Of the 395 patients with renal stones, 21% (n = 81) had at least one symptomatic stone event over the 10-year follow-up period.
The natural history of small asymptomatic renal stones has been described in a few key papers from mainly single institution case series which have reported conflicting results.
Glowacki et al. [19] prospectively followed up 107 patients for a mean of 31 months and reported a symptomatic event in only 32%, whereas 68% remained symptom free with the number of stones and a past history of stones being predictors of observation failure.
Of the patients with symptoms, 47% passed their stone spontaneously, 26.5% required surgical intervention and 26.5% had ESWL.
Burgher et al. [20] retrospectively assessed 300 patients with a mean follow-up of 38 months and showed 77% of patients progressed with regards to stone size, number and symptoms, of which 26% required an intervention. Patients with stones larger than 4 mm or those with lower pole stones were more likely to increase in size, develop symptoms or require intervention.
A further retrospective study by Kang et al. [21] of 347 patients reported 53% having a symptomatic stone event within 31 months follow-up of which 24.5% required an intervention with only 5% needing surgery. A stone event was more likely in those who were young, male and had a stone history.
In a more contemporary series Dropkin et al. [22] followed up 110 patients for over 3 years (mean stone size 7 mm) with only 24% becoming symptomatic and 19% requiring surgical intervention. However, 19% increased in size and only 2.9% passed the stone spontaneously.
Finally, a prospective randomised controlled trial (RCT) comparing observation to prophylactic ESWL in asymptomatic renal stones less than 15 mm reported no significant difference in terms of symptoms, requirement for additional treatment, quality of life or hospital admission during a 2-year follow-up period, with only 9% requiring surgery [23].
In summary, the natural history of small asymptomatic renal stones remains unclear; however, a period of observation appears to be a safe initial treatment option. Long-term follow-up is necessary especially in patients with increased risk of stone progression where the need for future active treatment is higher.
Q. The patient chooses a period of observation as his initial management. What is your follow-up regime and what are your indications for treatment?
A. I would follow-up this patient initially on a 6-monthly basis in a dedicated stone clinic to assess for symptoms and stone growth. If the stone was visible on the initial CT scout film I would use an x-ray KUB to assess for stone progression. If there was no growth and the patient remained asymptomatic I would consider increasing the follow-up to 12 monthly and discharging after 5 years. If the patient became symptomatic I would arrange a repeat CT-KUB to accurately assess his stone burden and help guide further management.
The majority of articles previously discussed have shown that progression is linked to stone size. The spontaneous passage of stones appears higher for <5 mm compared to 5-10 mm with some authors recommending the treatment of all renal stones >5 mm [24,25]. The EAU 2017 guidelines recommend the treatment of renal stones in patients with stone growth (>5 mm), de novo obstruction, associated sepsis, patient preference, social situation (professional or travelling), stones in patients at high risk of recurrence, solitary kidneys, women planning on getting pregnant and in patients with chronic pain. The recommended treatment options are discussed previously [8].
Q. Are there any specific occupations that you would be more likely to treat?
A. The Civil Aviation Authority (CAA) has a formalised guideline for the management of pilots diagnosed with one or more asymptomatic renal stones. ttey are deemed unfit to fly until they have been fully investigated and have been proven radiologically to be stone free after treatment. The UK Royal Air Force also requires the pilot’s metabolic stone profile to be normal before the pilot can return to work. In addition, patients whose jobs have the potential to risk the safety of others during an episode of renal colic (driving heavy good vehicles, trains, buses, etc.) should be advised that they are not fit to carry out their work until they are stone free and they should inform their employer and the Driver and Vehicle Licensing Agency as soon as possible [26].