We read the above article with great interest [1]. The authors suggested that the severity of urinary symptoms is associated with increasing use of ketamine and it improves with abstinence. We have also noticed these phenomena since the first description of the problem in 2008 [2]. However, we do not know whether the symptom change correlates with the severity of the urology sequelae, which will have significant long-term implications for the patient's medical health. To date, we are still lacking an objective clinical symptom scale that could accurately predict the severity of the detrimental effects of ketamine on the urinary system, i.e. endoscopic cystitis changes, decrease in bladder compliance and bladder capacity, detrusor instability, VUR and hydronephrosis etc.

In our previous studies, we observed that both the symptomatology and the histological appearance of bladder biopsies in these patients mimicked interstitial cystitis [3], we then used the Pelvic Pain and Urgency/Frequency (PUF) Patient Symptoms Scale by Pearson to correlate with these findings [4]. This Symptoms Scale has been used as an assessment tool for patients with interstitial cystitis. We validated the Chinese version of this PUF Symptom Scale for use in the local community. Our group found a high positive prediction accuracy for urological sequelae, namely endoscopic cystitis changes [mean (sd) PUF, 24.0 (6.4) vs 18.6 (7.4); P= 0.024), detrusor overactivity [mean (sd) PUF, 25.3 (4.9) vs 19.4 (7.8); P= 0.034], VUR [mean (sd) PUF, 30.0 (5.6) vs 20.3 (7.1), P= 0.029], poor bladder compliance [mean (sd) PUF, 27.2 (5.0) vs 18.6 (6.9); P= 0.001], and hydronephrosis [mean (sd) PUF, bilateral 30.0 (7.1) vs unilateral 22.5 (4.1) vs negative 20.6 (8.0); P= 0.018][4]. It was found that a threshold value of 17 is suggestive of more severe disease status, as all patients with abnormal sequelae mentioned above had PUF scores of >16. More importantly, the negative predictive value was 100 % using this threshold value for the more severe urological sequelae. We think that the adoption of this PUF Symptom Scale could spare ketamine abusers with scores below the threshold (i.e. ≤16) from invasive investigations.

We think that this PUF Symptom Scale could be a useful tool in screening studies like that reported in this article [1]. The follow-up of the data with time in the same study group will shed more light on the natural history of the problem. Experience has shown us that investigating this group of subjects can be extremely difficult due to their poor compliance to investigations and clinic visits. Moreover, it would not be practical to investigate all recreational drug users and manage their possible urological sequelae in a clinical setting. The adoption of the PUF Symptom Scale in the assessment could definitely give additional value to similar types of study projects by helping to screen out more severe cases requiring early medical or surgical interventions.