Retrospective interview-based long-term follow-up study of cats diagnosed with idiopathic cystitis in 2003–2009

Abstract

Objectives

The aim of this study was to register long-term recurrence rates and mortality rates in cats diagnosed with feline idiopathic cystitis (FIC), with an observation period until death or a minimum of 10 years.

Methods

Data regarding recurrence of signs of feline lower urinary tract disease (FLUTD) and FLUTD-related mortality in cats diagnosed with FIC between 2003 and 2009 were obtained through structured telephone interviews with the cat owners from December 2018 until February 2019. The interviews were based on a standardised questionnaire covering whether the cat was still alive or not, whether death/euthanasia were due to FLUTD and whether the cat had experienced recurrent episodes of clinical signs of FLUTD. If recurrences had occurred, exact numbers or estimates of 1–3, 4–6 or >6 recurrences were recorded.

Results

The owners of 50/105 FIC cats included in a previous study (48%) were available for inclusion in the present study. At the time of the interview, only 6/50 cats (12%) were still alive. The FLUTD-related mortality rate was 20% (n = 10/50). Twenty-three cats (46%) had no recurrences, three cats (6%) were euthanased shortly after diagnosis, nine cats (18%) had 1–3 recurrences, three cats (6%) had 4–6 recurrences and six cats (12%) had >6 recurrences. For the remaining six cats, the number of recurrences was uncertain.

Conclusions and relevance

The long-term prognosis for cats diagnosed with FIC may, based on the results from the present study, be regarded as fairly good, as approximately 70% of the cats either recovered without additional episodes, experienced only a few recurrences, are still alive after a minimum of 10 years since inclusion in the study, or were euthanased for reasons unrelated to FLUTD.

Introduction

Cats with feline lower urinary tract disease (FLUTD) present with clinical signs such as stranguria, dysuria, pollakiuria, haematuria and/or periuria. ¹ These signs are not indicative of a specific aetiology and may result from infections, uroliths, urethral plugs, neoplasia, anatomical abnormalities, and traumatic, neurological or iatrogenic causes.^1–7 However, in a large proportion of cats with signs of FLUTD, thorough diagnostic investigation does not reveal a specific cause. These patients are classified as having feline idiopathic cystitis (FIC).^1,8–14

FIC has much in common with interstitial cystitis/bladder pain syndrome in humans, including the clinical signs, a tendency to reoccur, comorbid conditions and a relation to stress.^14–17 Despite years of research, the aetiology is still incompletely understood and, subsequently, diagnostic markers and consistently effective treatment are lacking.^13–16

Inappropriate urination is an important reason for cats being relinquished to animal shelters or euthanased.^18,19 Recurrent episodes of FIC are reported in 39–65% of the cats within 1–2 years of the initial episode,^14,16 but, until recently, little information was available on long-term prognosis and risk of euthanasia in cats with FLUTD. In 2019, Kaul et al ²⁰ published recurrence and mortality rates for cats with various causes of FLUTD. They reported an overall recurrence rate of 58.1% (all FLUTD cats, n = 101), among the FIC cats only (n = 52), the recurrence rate was 61.5%. Mortality due to FLUTD (5%) was lower than previously reported. ²⁰ In addition, Kaul et al ²⁰ found that 28% of cats experiencing a recurrence were diagnosed with different causes of FLUTD during separate episodes. This is in accordance with another report, and indicates a need to include lower urinary tract signs in general, rather than specific diagnoses, in retrospective studies of recurrences in cats with FLUTD. ²¹

The aim of the present study was to register the long-term recurrence rates and FLUTD-related mortality rates in cats diagnosed with FIC with an observation period until death or for a minimum of 10 years.

Materials and methods

The study was a retrospective descriptive study using telephone interviews based on a standardised questionnaire. Owners of cats diagnosed with FIC between 2003 and 2009 were interviewed in 2018/2019 regarding the recurrence of signs of FLUTD and FLUTD-related mortality.

Animals

The study population consisted of client-owned first-opinion cases presented to the Small Animal Clinic, Department of Companion Animal Clinical sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU). Cats that were diagnosed with FIC in a prior study of FLUTD in Norway between 2003 and 2009 were eligible for inclusion.^22,23

Data collection

A standardised questionnaire was designed consisting of questions regarding the recurrence of FLUTD signs and FLUTD-related mortality. In order to identify unintelligible questions and sources of misinterpretation, the questionnaire was tested in a pilot study in a focus group (n = 5) consisting of veterinarians, veterinary students and cat owners. There were seven questions in the questionnaire. The owners were first asked if the cat was alive. If not, age at death, how the cat died and whether the cat was dead or euthanased owing to FLUTD was registered. Further, occurrence of recurrent episodes after the first episode of FIC was noted and, if present, the number of recurrent episodes were registered. If the owners were unable to give an exact number of recurrent episodes, the owners were asked to give an estimate of 1–3, 4–6 or >6 episodes.

A separate episode was defined as the recurrence of signs of FLUTD after a period of at least 4 weeks without any clinical signs. Owing to the long observation period, the owners were asked about the recurrence of clinical signs like difficulties with urination and blood in the urine rather than diagnoses like FIC, in order to reduce the level of recall bias. The observation period lasted from diagnosis until the telephone interview or the death of the cat.

The telephone numbers of the cat owners were obtained from the patient database at NMBU. In cases of missing, outdated or incomplete contact information, internet search engines (www.telefonkatalogen.no and www.1881.no) were used to retrieve current information. At least three attempts were made to reach each of the owners. The interviews were performed from December 2018 until February 2019 by three of the authors. A script was made, and each interview began with an introduction explaining the purpose of the study, followed by structured questions. Initially, attempts were made to validate the information obtained from the owners against medical records. However, the medical records obtained were of mixed quality, incomplete and not all recurrences led to veterinary consultations. Therefore, a decision was made to focus on owner information only. Permission to perform the study was granted by the research and ethics committee at the NMBU, as well as from the individual owners.

Statistical methods

The results are presented as frequencies of occurrence, expressed in percentages for categorical variables and mean, median and range for assumed continuous variables. Statistical analyses were performed in JMP 10 (SAS Institute) using t-test and ANOVA for the assumed continuous variables and contingency table analysis, and χ² tests for categorical variables. Differences were considered significant at P <0.05.

Results

While 105 cats were found eligible for inclusion, 55 of the owners could, for various reasons, not be reached. Therefore, 50 cats were included in the present study. Of the included cats, 42/50 (84%) were domestic shorthair or domestic longhair, and 8/50 (16%) were purebred cats. Thirty-nine (78%) were neutered males, one (2%) was an intact male, eight (16%) were neutered females and two (4%) were intact females. At the time of diagnosis (between 2003 and 2009), the mean age of the 50 cats later included in the present follow-up study was 6.5 years (median 5.5 years; range 1–18 years). The majority had non-obstructed FIC (96%) and 36% had experienced prior episodes of FLUTD. The follow-up period ranged from 0 to 16 years, as some cats were euthanased directly after diagnosis, with a mean and median of 8 and 9 years, respectively.

Mortality

An overview of the included 50 cats is given in Figure 1. At the time of the telephone interviews, 6/50 cats (12%) were still alive, while 43/50 (86%) were dead or had been euthanased, and 1/50 (2%) had an unknown status due to rehoming. In more detail, 10/50 cats (20%) were dead or had been euthanased owing to FLUTD and 27/50 (54%) were euthanased for other causes (not registered in the present study). Of the remaining cats, 5/50 (10%) had died of natural causes, 1/50 (2%) was either dead of natural causes or had been euthanased (the cat was rehomed in the last 2–3 years of its life and the original owner knew the year of death but not how the cat died) and the last cat was successfully rehomed (owing to FLUTD) but later lost to follow-up.

Figure 1.

Overview of the cats with feline idiopathic cystitis (FIC) eligible for inclusion (n = 105) and those eventually included in the study (n = 50).

FLUTD = feline lower urinary tract disease

For the cats that were euthanased owing to FLUTD, mean and median life span after diagnosis were 3.6 and 5 years, respectively (range 0–9 years). Mean and median age at death were 11.6 and 12 years. For the cats euthanased for causes other than FLUTD, mean and median life span after diagnosis were 7.7 and 9 years, respectively (range 1–14 years), and mean and median age at death were 13.9 and 15 years, respectively.

Although the cats euthanased as a result of FLUTD tended to have a shorter lifespan than those euthanased for other causes, the difference was not statistically significant (P = 0.14). Age at initial inclusion until euthanasia for the individual cats in the two groups is shown in Figure 2.

Figure 2.

(a) Age (years) from initial diagnosis to euthanasia in cats euthanased owing to feline lower urinary tract disease (FLUTD) (n = 10). (b) Age (years) from initial diagnosis to euthanasia in cats euthanased for causes other than FLUTD (n = 27)

Recurrent episodes

Twenty-three of 50 cats (46%) did not have any recurrences. Three cats (6%) were euthanased shortly after inclusion and diagnosis. Twenty-three cats (46%) had one or more recurrent episodes; 9/50 (18%) had 1–3 episodes, 3/50 (6%) had 4–6 episodes and 6/50 (12%) had >6 episodes, while the owners of five cats (10%) could not specify the number of recurrences. The remaining cat was successfully rehomed owing to its urinary problems but was later lost to follow-up after 10 years. Its final outcome is, therefore, unknown.

Of the six cats with >6 episodes, 1/6 cats had seven episodes, 1/6 cats had 10 episodes, 2/6 cats had 20 episodes and 1/6 cats had persistent FLUTD. The distribution of the number of recurrences within the groups of cats euthanased owing to FLUTD or for other causes is shown in Figure 3. As is to be expected, cats euthanased owing to FLUTD were significantly more likely to experience a higher number of recurrences compared with cats euthanased for causes other than FLUTD (P = 0.024). Obstructed vs non-obstructed recurrences were not registered.

Figure 3.

Number of recurrent episodes with regard to whether the cat was euthanased owing to feline lower urinary tract disease (FLUTD) or not (n = 50)

Discussion

The present study investigated long-term recurrence rates and FLUTD-related mortality rates in cats diagnosed with FIC 10–16 years ago. All cats in the study sample were first-opinion cases and causes of FLUTD other than FIC were excluded by thorough clinical investigation. Unfortunately, only 50 (48%) of the cat owners included in the original study from 2003 to 2009 were available for participation in the present follow-up study, mainly owing to changes in addresses and telephone numbers. ²³ Owing to the length of the study period, obtaining updated contact information was unsuccessful for the remaining owners.

Recall bias represents a substantial challenge in a study covering a time period of minimum 10 years or to the death of the cat. ²⁴ Studies comparing information from questionnaires and/or structured interviews with medical records show that recall bias is a potential limitation, and also that the level of agreement varies with the type of factor investigated.^24–26 Medical records are generally considered the gold standard, but the quality of these may represent an important limitation. In addition, not all medical conditions lead to consultations with health personnel and a subsequent registration in medical records; for example, milder episodes of FIC.^24–26 In the present study, the owners’ ability to remember specific diagnoses and the exact number of recurrences was considered doubtful. In order to reduce a potentially substantial bias, the owners were only asked for recurrence of clinical signs and not specific diagnoses. As the owners had already witnessed an episode of FIC, it was probable that they would recognise the clinical signs if reoccurring. While remembering the exact number of recurrences can be difficult, one may assume that most owners remember if there were none, a few or many.

In general, mortality in cats with FIC or FLUTD is difficult to assess owing to variations in study design and the population of cats (obstructed/non-obstructed/both) in the studies available for comparison. Mortality rates ranging from 8.5% to 26% have been reported.^12,27,28 In the present study, including FIC cats exclusively and a follow-up period of 10–16 years or to the death of the cat, only 12% of the cats were still alive and the FLUTD-related mortality rate was 20% (n = 10/50). This is higher than the mortality rate of 5% reported in another recent study regarding recurrence rate and the long-term course of cats with various lower urinary tract diseases. ²⁰ The study by Kaul et al ²⁰ had a follow-up length of 0.5–138 months and 73.3% of the cats were still alive when the study was conducted. The difference in mortality rate between these two studies (5% vs 20%) could be explained by the longer follow-up time in the present study. Several of the cats reported in the present study as having been euthanased owing to FLUTD were either diagnosed at a relatively old age or had lived for several years with their lower urinary tract disease before being euthanased as older cats. Thus, the increasing age of the cats may have been an important factor equivalent to the disease itself regarding the decision to euthanase.

Regarding mortality rates, there is great variation between studies, which is also true regarding reported recurrence rates, which range from 17% to 78%.^{2,12,14,20,27–32} In the present study, 52% of the cats (n = 26/50) experienced one or more recurrences. Again, the study performed by Kaul et al ²⁰ appears to be best suited for comparison with the present one. ²⁰ They found that 58.1% of all cats in their study, irrespective of underlying cause, had recurrent signs of lower urinary tract disease. Of the cats diagnosed with FIC, the corresponding percentage was 61.5%. The remaining studies available for comparison included none to considerably shorter follow-up periods than the present study,^2,30 were focused primarily on cats with urinary obstruction,^27,28,33 and/or included a study population dominated by referral cases, which may lead to a selection of the more severe cases.^12,31

Cats euthanased owing to FLUTD were significantly more likely to have a higher number of recurrences; the majority had experienced more than six additional episodes of FLUTD or were euthanased at the time they were diagnosed. Unfortunately, only information concerning the number of recurrent episodes and the time period the cats lived with their diagnoses was obtained in the present study. It is unknown when the episodes occurred, whether there were frequent episodes shortly after inclusion or whether there was a more sporadic distribution of recurrences throughout the lifespan of the cats. Kruger et al ³¹ found that increasing age was significantly associated with lower risk of recurrent episodes. Reduced risk of recurrent clinical signs and thus also a reduced risk of euthanasia owing to the disease over time is supported by the results from the study performed by Kaul et al, ²⁰ where deaths due to FLUTD were reported to occur within the first 24 months of an observation period up to 138 months. ²⁰ Also in the present study, 50% of the euthanasias owing to FLUTD were performed within 2 years. However, the other half of the cats reported as euthanased for FLUTD actually lived for quite some time after inclusion in the present study. Why some cats live to an old age despite suffering from recurrent signs of FLUTD may depend on several factors. With regard to prognosis, the number, frequency and severity of the episodes of lower urinary tract signs are obviously crucial factors. However, possible comorbidities and owner dedication are also important. As mentioned, urination in inappropriate locations is one of the main reasons owners relinquish their cats.^18,19The pathogenesis of FIC is still an enigma, and although stress is highly associated with the development of FIC, identification of possible stressors in a cat’s life may be challenging. ¹⁶ The impact of a single, limited stressful event is likely to differ from the impact of repeated events or more chronic situations. Furthermore, one cannot presume that all recurrences of clinical signs of FLUTD were due to FIC in the present study. Recurrent episodes due to different aetiologies have been described previously and occurred in as many as 28% of the cats in the study performed by Kaul et al.^20,21

Given the aforementioned limitations, such as failure to reach half of the cat owners from the previous case-control study of FIC cats, lack of validation against medical records and the possibility of recall bias, the present study would have provided a more complete insight into the prognosis of cats diagnosed with FIC if the cats had been followed prospectively after diagnosis, with structured owner observation and owner interviews at regular intervals. The study timeframe is at the same time both the strength and the weakness of this study.

Conclusions

The long-term prognosis for cats diagnosed with FIC may, based on the results of the present study, be regarded as fairly good, as approximately 70% of the cats either recovered without additional episodes, experienced only a few recurrences, are still alive after a minimum of 10 years since inclusion in the study or were euthanased for reasons unrelated to FLUTD. This is, to our knowledge, the first study to describe the prognosis in FIC cats based on a follow-up period almost equivalent to a cat’s natural lifespan.