Anal glands in dogs: clinical signs of infection
Introduction
The anal sacs located on either side of the anus of cats and dogs contain two small glands which release a lubricating substance to facilitate defecation. Each anal sac serves as a store for the fluid secreted by the glands. There is a single excretory duct running from each gland, inside the two sacs, to the anal canal.
They generally produce an unpleasant but functional odour, as it also helps identify themselves to their peers. The glands are susceptible to inflammation and infection, producing a clinical picture of pain and discomfort, and consequently a fairly characteristic behaviour in dogs. The problem repeats over time. It can affect one or both glands.
Anal gland infections in dogs: aetiology
The aetiology of anal gland infections in dogs remains unclear, but we are aware of several predisposing factors, such as breed, recent episode of diarrhoea or chronically soft stools, glandular hypersecretion associated with seborrhoea and poor muscle tone in obese dogs. The retention of faecal material predisposes infection and immune reactions that trigger the formation of abscesses.
Anal sac diseases are rare in cats, with impaction being the most common sign if one does develop.
Clinical signs
Anal sac diseases follow three different clinical patterns:
- Anal sac impaction: characterised by the accumulation of a pasty fluid, or a paste that is hard to expel by pressing on the inflamed anal sac.
- Anal sacculitis:inflammation, infection of such fluid.
- Abscess formation: characterised by the discharge of pus (mixed with blood) when the inflamed anal sac is pressed.
These are probably three forms of clinical presentation corresponding to different stages of the disease’s evolution.
Patients may also suffer from anal fistulas. In this case, the anal opening and/or impacted anal sacs become infected, leading to inflammation of the mucosa which may shrink and rupture the gland inward toward the deep tissues or cause the outward drainage of a blood and pus-filled fluid. Impaction is sometimes caused by the presence of faecaliths in the anal sacs. This problem is more complex in terms of its clinical signs, which include constipation, a foul odour, rectal pain and/or rectal secretion.
Tumours, such as apocrine gland adenocarcinoma of the anal sacs, may also occur and feature regional lymphatic metastasis. In this case, a mass can be palpated in an anal sac or the pararectal region, with paraneoplastic hypercalcaemia leading to anorexia, weight loss, vomiting, polyuria, polydipsia, constipation, dyschezia, ribbon-like stools and perianal inflammation. It often metastasises to the lymph nodes and less frequently to the liver, spleen and lungs.
Among the clinical signs associated with anal gland infections, and depending on the severity, we can observe tenesmus, anal pain and pruritus, tail chasing, anal fistulas, scraping the anus against an object or along the ground, mood changes and a “hot spot” in the lumbosacral region. Signs of more severe cases include painful swelling and inflammation of the perineal region, visible drainage ducts, dyschezia (difficult and painful defecation), constipation and occasionally fever. Any fluid discharge is greyish-brown.
The differential diagnosis should include all diseases affecting the anal and perineal region that can course with clinical signs of perianal fistulas, bites, circumanal gland (hepatoid) tumours and all types of trauma caused by tearing.
It is a problem that often recurs with time and can affect one or both glands.
Treatment of anal sac abscesses
Most animals are able to empty their own anal sacs. However, some of them lose this ability, which can cause health problems, as explained above.
Treatment varies depending on the clinical stage of the infection. So, in cases of impaction and sacculitis, it is advisable to drain the contents of the sacs manually, either internally (less painful) or externally. If possible, treatment should also include an antibiotic ointment and corticosteroids applied inside the sacs. Alternatively, in the case of an abscess, a systemic antibiotic therapy, such as amoxicillin/clavulanic acid, must be administered and the abscess treated in the usual way (hydrogen peroxide, povidone-iodine, antibiotic ointment). For recurrent abscesses, anal sac resection is indicated via surgery or chemical cauterisation.
Various studies have reported on the treatment of anal sac apocrine gland adenocarcinomas in which they surgically removed the sacs with or without adjuvant chemotherapy.
In addition, a high-fibre diet in combination with good hygiene of the perineal area is recommended for animals that frequently suffer impaction of the anal glands.
Prognosis
The prognosis is usually good, even if the glands need to be excised, since postoperative complications are rare. However, surgical complications include permanent faecal incontinence. Cases presenting with fistula formation or tumours have a guarded prognosis.
