Reflex dyssynergia in the male dog: the interrupted stream
5-year-old neutered male German Shepherd. He starts urinating with a normal stream, which stops abruptly after a few seconds; he keeps straining and only dribbles. Neurological examination is normal, a urethral catheter passes without resistance and post-void residual volume is markedly increased. Urinalysis and radiographs are normal.
What is the most likely diagnosis and its treatment?
chevron_right Show answer and explanation
A. Obstructive urethrolith: cystotomy and removal
A mechanical obstruction would prevent or hinder catheter passage and is usually visible on imaging; here the catheter passes easily and radiographs are normal.
B. Urethral sphincter incompetence: phenylpropanolamine
Urethral incompetence causes passive leakage without straining. Here the problem is the opposite (excess urethral resistance), and phenylpropanolamine would worsen it.
C. Bacterial cystitis: antibiotic based on culture
Cystitis causes pollakiuria and stranguria with small voids, but not an abrupt interruption of the stream with a large residual volume, and urinalysis is normal.
D. Reflex dyssynergia: alpha-blocker urethral relaxant (prazosin or tamsulosin) plus a striated muscle relaxant if needed
Correct. Detrusor contraction is not accompanied by urethral relaxation, so the urethra closes mid-voiding. It is typical of large-breed male dogs without other neurological deficits. It is treated with alpha-blockers and, if needed, diazepam or dantrolene, emptying the bladder meanwhile.
lightbulb Key takeaway
Watch the dog urinate: a normal stream that stops followed by straining is the dyssynergia pattern. Rule out mechanical obstruction first (catheter, imaging, urethrography). Measure post-void residual volume and keep the bladder empty to prevent overdistension atony while treatment takes effect.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.