Guarded long-term prognosis in male cats with urethral obstruction

Abstract

The aim of this study was to evaluate the course of urethral obstruction in cats. Forty-five male cats with urethral obstruction or lower urinary tract signs referable to urethral obstruction were included in the study. Follow-up information was gained by telephone interview in most cases and was available in 39 cats. Of the 22 cats with idiopathic urethral obstruction, eight (36%) re-obstructed after 3–728 days (median 17 days). Of 10 cats with urolithiasis, three (30%) re-obstructed after 10, 13 and 472 days, respectively. Of the seven cats with urethral plugs, three (43%) re-obstructed after 4, 34 and 211 days, respectively. Recurrent signs of lower urinary tract disease including obstruction were common in cats with urethral obstruction (20/39; 51%) and occurred in the same frequency irrespective of the primary cause of the obstruction. Recurrent obstruction (14/39; 36%) was the most common reason for euthanasia and was performed in 8/39 (21%) cats.

Hospital proportional morbidity rate (frequency with which the disease was diagnosed in veterinary hospitals) of urethral obstruction in cats was reported to be 1.5% between 1980 and 1999 in veterinary teaching hospitals in the USA (Lekcharoensuk et al 2002). Of cats with lower urinary tract disease, 18–58% were reported to be obstructed (Kruger et al 1991, Barsanti et al 1996, Lekcharoensuk et al 2001, Gerber et al 2005). Urethral obstructions were classified in studies from Kruger et al (1991) and Barsanti et al (1996) as urethral plugs (59% and 42%, respectively), idiopathic (29% and 42%, respectively), uroliths (12% and 5%, respectively) and strictures (0% and 11%, respectively). Urinary tract infections were involved in some of the cases. Other possible reasons for obstructions such as neoplasms, phimosis, primary and iatrogenic disorders were not mentioned (Osborne et al 2000).

Lower urinary tract signs resulting from urethral obstruction require immediate treatment, usually combined with hospitalisation. Therapy of urethral obstruction includes correction of fluid, electrolyte and acid–base derangements, re-establishing patency of the urethra under general anaesthesia, and possibly, placement of an indwelling catheter (Westropp et al 2005). Surgery to remove uroliths or to perform perineal urethrostomy is required in some cases. Thus, the therapy for urethral obstruction is costly and both short-term and long-term prognosis should be discussed with the owner. However, there are few data about prognosis. In one study published more than 25 years ago, 16% of cats died because of urethral obstruction, and 35% suffered from recurrence of the obstruction (Bovee et al 1979). More recent data are not available, even though causes of urethral obstruction seem to have changed over the years. In a recent study, the hospital proportional morbidity of urethral obstruction declined significantly from 1.9% in 1980 to 0.7% in 1999, and the percentage of cats with urethroliths or urethral plugs as cause of obstruction declined from 49% to 23% (Lekcharoensuk et al 2002).

This change in frequency of uroliths and urethral plugs might also influence the outcome of cats with urethral obstruction. The aim of this study was, therefore, to evaluate the outcome of urethral obstruction in cats currently presented to our hospital.

Materials and methods

Forty-five male cats diagnosed with urethral obstruction were admitted to the Clinic for Small Animal Internal Medicine, University of Zurich, between December 2000 and November 2002. A cat was considered obstructed if the bladder was distended and the cat was unable to void urine freely. Obstruction was also diagnosed when the bladder size was normal but calculi were seen in the urethra or obvious resistance was experienced with catheterisation. Diagnostic investigation included history, clinical examination, urinalysis, urine culture, haematology, serum biochemistry, radiography (including contrast radiography of the lower urinary tract when indicated), ultrasonography, and urethroscopy (‘micro’ Bendoscope with 1 mm diameter, Acutronic Medical Systemes AG; Baar, Switzerland); not all procedures were performed in each cat.

Body condition of each patient was assessed as overweight, normal or thin, based on observation, palpation (especially of the rib fat cover) and body weight. Urinalysis included determination of urine specific gravity by refractometer, dipstick chemistry (Combur-Test; Roche Diagnostics, Germany), urine sediment cytology and, in some cases, determination of an urine protein-to-urine creatinine ratio. Qualitative urine culture was performed on sheep blood agar and P05021, Gassner Medium (Oxoid GmbH, Wesel, Germany). Contrast radiography, when performed, consisted of retrograde urethrography, double contrast cystography and/or excretory urography. Urinary calculi were analysed by X-ray diffractometry and if appropriate by infrared spectroscopy.

Idiopathic urethral obstruction was diagnosed when no specific cause of the clinical signs could be identified (Osborne et al 2000). Urolithiasis was diagnosed by radiography, ultrasonography or cystotomy. Urethral plugs were diagnosed when a plug was identified during urethral catheterisation or by urethroscopy.

Follow-up evaluation was performed by reviewing the animals' medical records and by telephone interviewing the owner. Data collected included the length of hospital stay, immediate treatment, treatment after discharge, time to recurrence of signs, nature of clinical signs (obstruction or other signs of lower urinary tract disease like haematuria, pollakiuria, stranguria, urination in inappropriate places and pain), time elapsed since last occurrence of clinical signs, details of housing and feeding, and if dead, whether death was related to the actual lower urinary tract disease or a later episode of urinary tract disease.

Statistical analysis

Results were analysed using a commercial computer programme (SPSS Statistical Package for the Social Science 8.0 for Windows, SPSS Inc., Chicago). Comparisons of variables within and among groups were performed with the Mann–Whitney U test and a Fisher's exact test for association. Differences were considered significant at P<0.05.

Results

Forty-five cats were included in the study. Age, gender, and body weight of the cats are depicted in Table 1. Idiopathic urethral obstruction was diagnosed in 24/45 (53%) cats; 13/45 (29%) had urolithiasis, and 8/45 (18%) had urethral plugs. Follow-up information after discharge from hospital was available in 39/45 cats. Seven were re-evaluated at the clinic and 32 by telephone interview. An overview of follow-up information on the 39 discharged cats is given in Table 2.

Table 1.

Age, gender, and body weight of cats with urethral obstruction

Cause of obstruction	Age range (mean) [years]	Gender [n]		Body weight range (mean) [kg]
		Male neutered	Male intact
Idiopathic UO (n=24)	1–15 (5)	21	3	3.0–10.6 (5.8)
Uroliths (n=13)	3–15 (7)	12	1	3.9–7.0 (5.3)
Urethral plugs (n=8)	2–11 (4)	6	2	4.5–7.2 (5.7)
Total (n=45)	1–15 (5)	39	6	3–10.6 (5.7)

UO=urethral obstruction.

Table 2.

Overview of follow-up information on 45 cats with obstructive lower urinary tract disease

Diagnosis	Idiopathic UO (n=24)	Uroliths (n=13)	Urethral plugs (n=8)	Total (n=45)
Discharged	23	10	8	41
Available follow-up	22	10	7	39
Follow-up time [days]	5–868 (403) *	10–722 (512)	12–759 (405)	5–868 (432)
Still alive	16	8	6	30
Uneventful follow-up	11 (50%) †	5 (50%)	3 (43%)	19 (49%)
Follow-up time [days]	24–868 (398)	278–722 (671)	12–565 (559)	12–868 (517)
Recurrence of LUTD signs	11 (50%)	5 (50%)	4 (57%)	20 (51%)
Follow-up time [days]	5–827 (441)	10–551 (432)	349–659 (380)	5–827 (419)
Re-obstruction	8 (36%)	3 (30%)	3 (43%)	14 (36%)

UO=urethral obstruction and LUTD=lower urinary tract disease.

^*Range and median.

^†% Of cats in which follow-up was available.

The treatment of the cats consisted of re-establishing urethral patency and supportive care.

Cats with idiopathic urethral obstruction (n=24)

Twenty domestic shorthairs, one Persian, one Abyssinian, one Chartreux and one Maine Coon had idiopathic urethral obstruction. Lower urinary tract signs had occurred for the first time in 7/23 cats (30%). Previous history was not available in one.

The duration of hospitalisation ranged from 1 to 12 days (median 4.5 days). Treatment included urethral catheterisation in all, and indwelling catheters for up to 6 days (median 2 days) in 22/24 cats.

All cats were treated with intravenous crystalloid fluids (lactated Ringer's solution or saline 0.9%) and buprenorphine (0.006–0.014 mg/kg three to six times daily). Additional treatment included spasmolytics in 5/24 cats (diazepam 0.4–0.8 mg/kg one to two times daily or flavoxat 20 mg/kg three times daily or phenoxybenzamine 0.5 mg/kg once daily or methamizole 75 mg/kg once), non-steroidal anti-inflammatory drugs in 5/24 cats (tolfenaminic acid 20 mg/kg every other day or meloxicam 0.1 mg/kg once daily or carprofen 2.2 mg/kg once daily), heparin in 3/24 cats (70–90 IU/kg once to three times daily), and amitriptyline in 1/24 cats (5 mg once daily). Empiric antibiotic treatment was given after catheterisation in 16/24 cats (amoxycillin 19–23 mg/kg two to three times daily or amoxycillin/clavulanic acid 7–39 mg/kg twice daily or enrofloxacin 10 mg/kg once daily or cephalexin 27 mg/kg three times daily). Perineal urethrostomy was performed in 3/24 cats because of recurrence of obstruction after removal of the urinary catheter.

One cat died while in hospital; a cerebellar meningioma was diagnosed at necropsy. The remaining 23 cats were discharged and follow-up was available in 22: 18 by telephone interview and four by re-examination (Table 2). Treatment after discharge consisted of the recommendations to feed a wet cat food (17 cats) and in 12 cats to continue antibiotic treatment for up to 3 weeks (amoxycillin/clavulanic acid 8–17 mg/kg twice daily or enrofloxacin 10 mg/kg once daily or cephalexin 18 mg/kg twice daily). Non-steroidal anti-inflammatory drugs were prescribed in 7/23 cats (tolfenamic acid 4 mg/kg every other day or nifluminic acid 5 mg twice daily or carprofen 2–4 mg/kg once daily or mefenamic acid 0.05 mg once daily). Two cats were treated with amitriptyline (5 mg once daily) and one cat with N-acetyl-glucosamine (125 mg once daily).

Eight cats obstructed again, in four of them other lower urinary tract signs were seen before or after re-obstruction (Table 3). One cat which re-obstructed, subsequently had a perineal urethrostomy performed. One cat died at home 390 days after discharge. Dyspnoea was the major sign reported by the owner. This was not attributed to lower urinary tract disease.

Table 3.

Follow-up information of 20 cats with recurrent of signs of lower urinary tract disease after discharge

Diagnosis	Idiopathic UO (n=11)	Uroliths (n=5)	Urethral plugs (n=4)	Total (n=20)
Obstructed again	8	3	3	14
Follow-up time [days]	5–789 (26) *	10–472 (330)	349–659 (356)	5–789 (340)
Time to recurrence of signs [days]	3–183 (9)	10–472 (13)	4–211 (34)	3–472 (12)
Time to re-obstruction [days]	3–728 (17)	10–472 (13)	4–211 (34)	3–728 (18)
Number of recurring events	1–2 (2)	1–2 (1)	2	1–2 (2)
Dead due to LUTD	5	2	1	8
Without obstruction	3	2	1	6
Follow-up time [days]	817–827 (825)	432, 551	405	405–827 (684)
Time to recurrence of signs [days]	8–45 (42)	3, 274	3	3–274 (25)
Number of recurring events	2–7 (4)	1, 3	2	1–7 (3)
Dead due to LUTD	0	0	0	0

UO=urethral obstruction and LUTD=lower urinary tract disease.

^*Range and median.

Housing conditions after discharge were known from 14 cats and the type of food after discharge in 17 cats (Table 4). Cats living entirely indoors after discharge developed recurrent signs of lower urinary tract disease at the same rate as cats with outdoor access. The percentage of wet food fed after discharge was not significantly different between cats which had recurrent lower urinary tract signs and cats without.

Table 4.

Housing and feeding of cats after discharge

Diagnosis	Idiopathic UO	Uroliths	Urethral plugs	Total
Indoor only	6	3	4	13
Recurrent signs		3 (3) *	3 (2)	6 (5)
No recurrent signs	6		1	7
Outdoor access	8	2	1	11
Recurrent signs	3 (3)	1		4 (3)
No recurrent signs	5	1	1	7
Fed more than 80% wet food	9	3	1	13
Recurrent signs	4 (3)	2	1 (1)	7 (4)
No recurrent signs	5	1		6
Fed less than 80% wet food	8	3	4	15
Recurrent signs	3 (2)	1 (1)	2 (1)	6 (4)
No recurrent signs	5	2	2	9

UO=urethral obstruction.

^*Number of cats with re-obstruction.

Cats with uroliths (n=13)

Ten domestic shorthairs and three Persians in this study had uroliths. In 9/12 cats this was the first episode of lower urinary tract signs. Previous history was not available in one cat.

Radiography and ultrasound examination revealed stones in the bladder and the urethra in 6/13 cats. Stones were found in the bladder alone in 3/13 cats and in the urethra alone in 1/13 cats. Stones in the bladder and the kidney and stones in the bladder, the urethra, the kidney as well as in the ureter were found in 1/13 cats each. In 1/13 cats, uroliths were identified only during cystotomy. In this cat, contrast radiography was performed prior to surgery.

Two cats underwent immediate surgery without catheterisation and one cat was euthanased immediately after diagnosis. In the other cats, urethral patency was established and a closed urine system was kept for 1–4 days (median 2 days).

Owners refused surgery in 2/13 cats with urolithiasis; one of these was discharged after catheterisation and amitriptyline (5 mg once daily) as sole treatment, while the owner elected euthanasia in the other. Cystotomy was performed in 8/13 in order to remove the stones with a concurrent perineal urethrostomy in three of these. Perineal urethrostomy only was performed in one cat. In another with urethral urolithiasis, stones could no longer be seen on radiographs after catheterisation. It was suspected that the stone had been flushed out during catheterisation. One cat re-obstructed immediately after cystotomy and was subsequently euthanased.

Calcium oxalate uroliths were identified in 6/13 cats, struvite uroliths in 2/13 cats and the type of uroliths was not determined in the remaining five cats. Duration of hospitalisation ranged from 1 to 15 days (median 6 days). Ten cats were discharged. Treatment after discharge consisted of diet recommendation in six cats. In two cats diets to reduce the formation of struvite crystals were recommended (one cat with a struvite stone and one cat with an unknown stone). In two cats with calcium oxalate stones, diets to minimise recurrence of oxalate stones were prescribed. The owners of two cats were advised to add water to the food. In six cats antibiotic treatment after discharge was recommended (amoxycillin/clavulanic acid 13–16 mg/kg two to three times daily or cephalexin 17–20 mg/kg twice daily). Amitriptyline (5 mg once daily) was given to two cats. N-acetyl-glucosamine (250 mg once daily), potassium citrate (150 mg three times daily), phenylpropanolamine (1 mg/kg three times daily) and phenoxybenzamine (1.4 mg/kg once daily) were given to one cat each.

Follow-up was available in all 10 discharged cats and in nine through telephone interview. For one cat the medical record was available (Table 3). Two cats were euthanased after re-obstruction.

Housing conditions after discharge were known from five cats and the type of food after discharge from six cats (Table 3). Cats living entirely indoors after discharge developed recurrent signs of lower urinary tract disease at the same rate as cats with outdoor access. The percentage of wet food fed after discharge was not significantly different between cats which had recurrent lower urinary tract signs and cats without.

Cats with urethral plugs (n=8)

Five domestic shorthairs, one Norweigan Forest, one Persian and one Siamese had urethral plugs. Clinical signs of lower urinary tract disease were for the first time evident in three cats. In two cats, the urethral plugs were diagnosed by urethroscopy and in six by identifying plug material. Plain radiographs were made in all cats and ultrasound examinations of the urinary tract were performed in seven cats. In one cat, retrograde urethrography was performed to further evaluate the urethra after initial treatment.

Duration of hospitalisation ranged from 2 to 8 days (median 4.5 days). Therapy in hospital included catheterisation in all cats and indwelling catheters for up to 4 days (median 2 days) in 7/8 cats.

Intravenous crystalloid fluid (lactated Ringer's solution) was given to all cats, seven cats received buprenorphine (0.008–0.015 mg/kg three to eight times daily) and one cat butorphanol (0.01 mg/kg four times daily). Additional treatment consisted of carprofen (3 mg/kg once) and heparin (100 IU/kg three times daily) in one cat each. In all cats empiric antibiotic treatment was given after catheterisation (amoxycillin 20 mg/kg two to three times daily or amoxycillin/clavulanic acid 8–25 mg/kg two times daily). Perineal urethrostomy was performed in one cat because of renewed obstruction after removal of the urinary catheter. All cats were discharged.

Treatment after discharge consisted of a recommendation to feed wet cat food in five cats. Antibiotic treatment was continued in six cats (amoxycillin/clavulanic acid 8–14 mg/kg twice daily). One cat received amitriptyline (5 mg once daily) and one N-acetyl-glucosamine (250 mg once daily).

Follow-up in 7/8 cats was by telephone interview (5/7) or re-examination (2/7) (Table 3). Two had perineal urethrostomy performed after re-obstruction and one was euthanased.

Housing conditions and the type of food given after discharge were known from five cats (Table 4). Cats living entirely indoors after discharge developed recurrent signs of lower urinary tract disease at the same rate as cats with outdoor access. The percentage of wet food fed after discharge was not significantly different between cats which had recurrent lower urinary tract signs and cats without.

Comparisons among groups

Duration of hospitalisation, duration of closed urinary catheterisation system and follow-up times were not significantly different between the groups of cats. There was also no difference in the rate of re-obstruction between groups.

In 25% of the cats with uroliths it was not the first episode of lower urinary tract signs. This was significantly lower than in cats with idiopathic urethral obstruction (70%) and in cats with urethral plugs as cause of the obstruction (63%).

Outcome

Of the 43 cats with urethral obstruction in which information was available, 11 (26%) died or were euthanased because of their disease. Recurrent obstruction was the most common reason for euthanasia in nine of them. One was euthanased while in the clinic while the other eight were discharged. Two cats with urolithiasis were euthanased in the clinic after diagnosis without specific therapy. Two cats with idiopathic urethral obstruction died from causes unrelated to lower urinary tract disease.

Perineal urethrostomy was performed in 10/45 (22%) cats and led to resolution of clinical signs in 5/10 cats. Two re-obstructed and one of these was euthanased. The nine cats in which perineal urethrostomy was performed and that were still alive at the time of re-evaluation had been disease-free for 12–711 days (median 329 days).

In seven (35%) of the 20 cats with recurrent signs, lower urinary tract signs recurred within 7 days of discharge in 12 (60%) within the first 15 days, in 16 (80%) within the first 62 days and in four (20%) later than 180 days after discharge. There was no difference between the causes of urethral obstruction.

There was no difference in the rate of recurrence of complications or re-obstruction between cats presenting for the first time with signs of lower urinary tract signs and those that were presenting for a recurrence.

Overall recurrence of obstruction in cats older than 4 years was the same as in younger cats, however, the rate of recurrence was significantly less in the first 6 months after discharge. All cats having recurrence of obstruction 180 days or more after the recorded episode were older than 4 years.

Cats with re-occurrence of signs as well as cats with re-obstruction were significantly heavier than cats without complications.

Discussion

Based on this study, the long-term prognosis for cats with urethral obstruction is guarded. As described in a earlier study immediate treatment was successful in most cases and most cats could be discharged (Lee and Drobatz 2003). Only 4/45 (9%) cats did not leave the hospital in the present study. However, 51% of the cats with urethral obstruction had recurrent signs of lower urinary tract disease after discharge irrespective of the cause, 36% re-obstructed and 23% were euthanased due to lower urinary tract disease. It is important to be able to supply this information to owners in order to provide a realistic prognosis and to avoid disappointment after the treatment of this costly disease.

Only one other study has described the outcome in cats with urethral obstruction (Bovee et al 1979). Even though diagnosis in this study was feline urethral obstruction and no further details were given about how this diagnosis was established, a similar percentage of cats re-obstructed (35% compared with 36% in the present study). In the present study the initial diagnosis established in the clinic was clear, however, causes of re-obstruction were not known as most information was gained by telephone interview.

The frequency of obstructive lower urinary tract disease has declined over the last 20 years in veterinary teaching hospitals, but the present study indicates that there was no improvement in the prevention of re-obstruction in affected cats (Lekcharoensuk et al 2002). The decline in urethral obstructions is attributed to the development of diets minimising struvite crystalluria. These diets are also recommended to prevent recurrent struvite uroliths and urethral plugs containing struvite crystals. In cats with calcium oxalate stones, diets designed to prevent recurrence of these stones are recommended. However, in none of the diets has the effects been documented in clinical cases and increasing water consumption was considered the cornerstone of therapy for urolithiasis (Hostutler et al 2005, Westropp et al 2005). No treatment has rendered convincing results to prevent recurrence in cats with idiopathic urethral obstruction. However, feeding canned food has shown some promise in cats with non-obstructive idiopathic lower urinary tract disease. In one study, feeding a canned urinary acidifying diet reduced the recurrence rate in non-obstructive idiopathic cystitis compared to the same diet in a dry form; however, the study was neither randomised nor blinded (Markwell et al 1999). In another study oral glucosamine administration resulted in an improvement of clinical signs in both treated and untreated cats with non-obstructive idiopathic cystitis, which was attributed to the fact that the owners of affected cats started feeding canned food (Gunn-Moore and Shenoy 2004). In the cats described in the present study diets were only evaluated according to the moisture, specific diets with the possible benefit to minimise crystalluria were only recommended in few cats and not considered in the evaluation. Feeding moist food was recommended in most of the cats with idiopathic urethral obstruction and with urethral plugs, but not all owners followed the recommendations. Nevertheless, no difference in outcome could be recognised between those that were fed moist food and those that did not. Other treatments applied were very heterogeneous and the influence of each respective treatment on the outcome cannot be judged based on this study. Further measures recommended in cats with non-obstructive idiopathic lower urinary tract disease like placement and number of litter boxes and food bowls, environmental considerations, resting areas and social contacts were not routinely discussed with the owners of the cats in this study (Westropp et al 2005, Buffington et al 2006). This might have contributed to the unfavourable outcome in these cats.

In the present study, no difference could be found in the recurrence of re-obstruction or lower urinary tract disease signs between the different groups of cats. However, cats with uroliths experienced no immediate re-obstruction if the cause was correctly removed. Recurrence of struvite stones was reported to occur after a mean of 27 months (Albasan et al 2006). Only in two cats that had uroliths recurrence of signs could have been caused by reforming of stones as in the other three signs recurred within the first 2 weeks.

Perineal urethrostomy is considered to lead to a good long-term disease-free outcome in cats (Bass et al 2005). In our study, half of the cats in which perineal urethrostomy was performed had no further clinical signs. However, half of the cats did have recurrent signs similar to the cats without urethrostomy, and re-obstruction occurred in two (22%) cats. This is somewhat less than the 36% overall recurrence rate of obstruction, indicating that perineal urethrostomy does reduce re-obstruction but does not reduce recurrent signs of lower urinary tract disease.

Duration of hospitalisation was 1–15 days (median 5 days) in the present study. This was longer than in one other study where 12 discharged cats stayed only 2–5 days in the hospital (Drobatz and Hughes 1997). However, five of the cats were discharged because of financial and not medical considerations. Furthermore, surgery, which might have prolonged hospitalisation, seemed unnecessary in all of these cats.

Clinical signs of lower urinary tract disease described by the owner do not allow a specific diagnosis without further investigation. Clinical signs of lower urinary tract disease are similar regardless of the causes of the disease (Osborne et al 1996). Therefore, it was not possible to identify the causes of recurrent signs of lower urinary tract disease in this study. However, urethral obstruction was considered to be easily identified as immediate veterinary care was needed. Urethral spasms are considered a common reason for recurrence of obstruction, and antispasmodic medications have been recommended (Westropp et al 2005). But efficacy of these medications to prevent re-occurrence of obstruction has not been proven.

The effect of diet and husbandry on feline lower urinary tract disease has long been debated. Lower urinary tract disease (obstructive or not) has been associated with cats that are overweight, kept indoors and fed predominantly dry food (Willeberg and Priester 1976, Jones et al 1997). In the present study neither feeding dry food nor keeping the animal indoors influenced the outcome, irrespective of the cause of obstruction. However, the number of cats in this study was low reducing statistical power. Interestingly, cats that developed recurrent clinical signs including obstruction weighed significantly less at the time of presentation than the cats that remained asymptomatic. This would suggest that heavier cats might be at less risk of re-occurrence. However, as we had no data about weight at the time of re-occurrence of clinical signs, no conclusions can be drawn.

The proportion of cats with previous signs of lower urinary tract disease was lower in cats with urolithiasis than in the other two groups, but there was no detailed information available regarding previous episodes of lower urinary tract disease. One possible reason for this discrepancy might be that uroliths are easily identified and usually immediately treated, whereas there is no clear effective treatment and prophylaxis for idiopathic urethral obstruction and urethral plugs in which recurrence rates are high (Lulich et al 1996). However, this situation might be different following episodes of obstruction, as the frequency of re-occurrence of signs was not different between cats with uroliths and the other groups in the present study.

In contrast to the study of Bovee et al (1979), in which recurrence of obstruction was less common in cats older than 4 years, this was not the case in the present study. However, in Bovee et al (1979) only the first 6 months after obstruction were evaluated. If only the first 6 months were considered in the present study, cats older than 4 years obstructed significantly less often than younger cats. The reason for this is not obvious. The cats that obstructed after 6 months came from all diagnostic groups and did not show any other characteristic features other than being older than 4 years and having recurrent obstruction.

In conclusion, complications including recurrent obstruction are common in cats with urethral obstruction. The frequency of re-obstruction was similar to that in a study performed 25 years ago and was not influenced by the primary cause of the obstruction.