Urethral plugs in dogs

Abstract

Background: Crystalline-matrix urethral plugs have not been previously reported in dogs.

Hypothesis/objectives: To report the composition of urethral plugs in dogs, describe clinical features of the disease, and identify overrepresented breeds.

Methods: Retrospective case series. A Minnesota Urolith Center (MUC) record search was performed for urethral plugs in dogs submitted during a 6-year period. The composition of the plugs and signalment of affected dogs were recorded. Breed risk analysis was performed using a control group without plugs from the Veterinary Medical Center, University of Minnesota (VMC UMN). Breed risk was also calculated for a group of dogs with struvite (plugs and uroliths). Medical records for the subset of plug cases from the VMC UMN were reviewed and described.

Results: Between 2006 and 2011, 42 urethral plugs from dogs were submitted to the MUC. All came from male dogs, and the mineral component of the majority (83%) was struvite. Thirty (71%) samples were from Pugs. Pugs were overrepresented in plug submissions (OR 179; CI 88-389; P < .001), and for struvite in general (OR 14.3; CI 7.9-24.4; P < .001). Nine of the dogs were treated at VMC UMN; all were castrated male Pugs. None of these cases had bacteriuria or positive urine cultures, and no underlying cause of plug formation was identified.

Conclusions and clinical importance: When evaluating dogs with urethral obstruction, plugs need to be considered, especially in male Pugs. Further investigation into the underlying cause of plug formation in dogs is warranted.

Keywords: Lower urinary tract; Magnesium ammonium phosphate; Struvite; Urethral obstruction.

Figure 1

Survey abdominal radiograph of an 8‐year‐old castrated male Pug revealed mineral opacity throughout the bladder and proximal urethra. Large clumps of struvite crystalline material and several small struvite calculi were removed via cystotomy.

Figure 2

Urethral plug from a 2‐year‐old castrated male Pug protruding from the distal urethral opening. The crystalline portion of the plug was composed of 100% struvite interspersed in a matrix of cellular and proteinaceous material.

Figure 3

Contrast cystourethrogram from an 8‐year‐old castrated male Pug revealed numerous cystic and urethral calculi and a urethral diverticulum in the proximal urethra. Sludge‐like material and small uroliths (<1 mm) composed of 100% struvite were removed from the bladder and urethra via cystoscopy, followed by cystotomy.

Figure 4

H&E stained section of urethral plug at 10× magnification. Amorphous angular to slightly rounded clear spaces, that once contained struvite crystals that were lost in processing, within eosinophilic amorphous material that might represent proteinaceous debris and degenerate cells. A portion of the plug was submitted for quantitative mineral analysis; the crystalline portion was composed of 100% struvite.