Friday, October 18, 2013

Three things I learned: urinary incontinence in dogs

Dog pit stop.
Bosca and Phil queue for the gents.
Urinary incontinence is not uncommon in canine patients, but it can be extremely frustrating for affected dogs and owners alike. This week I attended a webinar given by BruceMackay hosted by the Australian Small Animal Veterinary Association (ASAVA). Not only is Dr Mackay a specialist in canine internal medicine, but he owns two dogs who suffer from (controlled) urinary incontinence, which gives him extra cred in this area.

In very basic terms, urinary incontinence occurs when there is too much or too little bladder or urethral tone, which can be due to a range of reasons including neurological to hormonal.

According to Dr Mackay, two things that are easily omitted during physical examination are palpation of the urethra (on rectal examination you should be able to palpate it travelling over the brim of the pelvis) and neurological examination (including looking at anal and tale tone and peri-anal sensation.

The session provided a nice refresher on incontinence, for which there are many differentials including:
Pathological process/disease type
Disease conditions
Ectopic ureters
Pelvic bladder (short urethra syndrome)
Vaginal stricture/stenosis
Urethrovaginal fistula
Patent urachus
Bacterial or fungal cystitis
Transitional cell carcinoma
Renal insufficiency/failure
Diabetes mellitus/diabetes insipidus
Phenobarbital/potassium bromide
Urethral sphincter mechanism incompetence
Lower motor neuron disease/peripheral neuropathy
Upper motor neuron disease

To this list I think it is important to add behaviour (some dogs will leak a bit of wee when they are excited, some will do it when they are anxious) and training (some dogs just aren't toilet trained...and some owners aren't always aware of the need to let their dogs out to pee regularly!). 

Haematuria often indicates a UTI but may also indicate prostate disease in male dogs.
The bladder and urethra are supplied by the hypogastric, pelvic and pudendal nerves. Damage to these nerves (for example from trauma or spinal tumour) may lead to urinary incontinence. Some studies have found a positive association with tail docking and many breeds prone (eg old English sheepdogs, German shepherds, Rottweilers, Weimaraners etc) are breeds which are traditionally docked – though tail docking has been banned in Australia for some time).

According to Dr Mackay, a thorough work-up for UI involves a CBC/MBA/UA + urine sediment exam and culture and sensitivity to rule out the majority metabolic and infectious causes. Imaging (sonography, plain and contrast radiographs, cystoscopy and urodynamic studies) may be warranted, especially in the work up of ectopic ureters.

Even so ectopic ureters can be challenging to diagnose as ureters are pulsatile and one can’t always easily see where these are entering the trigone of the bladder. One might need to used CT, vaginograms (Dr Mackay performs these if intravenous urography fails to yield a diagnosis) or fluoroscopy to catch these. Dr Mackay provided a detailed description of his techniques for these examinations.

One thing I learned is that in Australia at least, golden retrievers are over-represented when it comes to ectopic ureters and often these animals have “megaureters” which are thickened and torturous. As it seems with most terrible conditions of the urinary tract, females are more commonly afflicted than males.

Another thing I learned is that Aspergillus can cause a form of diabetes insipidus and affected dogs need to be on azoles for life.

Of course the most common cause of urinary incontinence by a mile is urethral sphincter mechanism incompetence (USMI).

There are oestrogen receptors located in the urethral mucosa, blood vessels and muscle. Oestrogen promotes tone in these structures. Oestrogen deficiency therefore is associated with reduced urethral tone and atrophy of urethral vasculature. Pressure from within the urethra exceeds that exerted by the urethra, and incontinence results.

Often the first sign of urinary incontience is that a dog wets the bed.
USMI is reported in up to 20 per cent of speyed dogs, with the average age of onset around 2.9 years – and largely breeds more likely to be affected (dogs over 15kg are 7x more likely to be affected). Current literature suggests that age of desexing is not a significant risk factor.

The treatment of choice is phenylpropanolamine (PPA), an alpha-adrenergic agonist which directly stimulates the urethral sphincter, at 1.1-1.5mg/kg PO TID initially, weaned down to the lowest effective dose. [In the good old days, before it was used widely for illicit purposes, pseudoephedrine was used for this purpose quite successfully].

Potential adverse effects include agitating, vomiting, panting, mydriasis, hypertension, tachycardia, bradycardia and seizures – but most dogs tolerate this well and the majority (Dr Mackay says around 75-85%) are well controlled on this medication.

Synthetic oestrogen (i.e. diethylstilboesterol or DES) is an alternative because this upregulates expression of alpha receptors. Around 50-65% of dogs have resolution of signs. This drug is often frowned upon due to the potential for bone marrow dyscrasias. Within the group (over 150 webinar delegates) only two vets had seen this – both around 20 years ago. [Interestingly, such dyscrasias are more likely to occur when oestrogen is administered after a mismating or when males suffer from oestrogen-secreting sertoli cell tumours]. The dose is around 1mg/day for 5 days then 1mg/week.

Some dogs require a combination of PPA and DES to control incontinence – at least initially. They have a synergistic effect in both upregulating (DES) and stimulating (PPA) alpha receptors.

These struvite cystoliths were passed by a schnauzer with incontinence. She also had a UTI.
Incontinent male does can be treated with PPA but prostate disease must be ruled out first. They can also be given testosterone cypionate (2.2mg/kg IM q 30 days) but ironically this can cause prostate disease – and aggression. Dr Mackay mentioned a case involving a male poodle with incontinence whose signs were resolved with physiotherapy alone. I hadn't realised this was an option.

When medical management doesn’t work, surgery is often required e.g. colposuspension or implantation of a hydraulic inflator, or, less invasive, urethral bulking agents. The latter provide relief of symptoms for a limited time as they flatten out after a while, opening the lumen of the urethra. Collagen was the substance of choice but as this is no longer available in Australia, “Bulkamid” is used instead.

One more thing I learned is that dogs with ectopic ureters can have concurrent USMI. That can be both a diagnostic and treatment challenge and may the reason that some dogs fail to respond to treatment.