Canine Anal Sacculitis: A Brief Review With a Focus on the Recent Literature

Most carnivores have paired, spherical pouch-like sacs bilateral to the anus with a single duct opening to lateral margins of the anal sphincter, termed anal sacs. These sacs serve as receptacles for the secretions of the apocrine and sebaceous glands, which line their walls and are thought to play a role in scent communication.¹ Anal sac contents are secreted passively during defecation but can also be actively expressed when a dog experiences fear. Problems arise when the anal sac contents are not evacuated normally and begin to build up, resulting in discomfort.² Non-neoplastic anal sac disease (NASD) can include anal sac impaction (anal sac overfilling), anal sacculitis (inflammation with or without infection), and anal sac abscessation (rupture of the anal sac, leading to cellulitis and deep infection of surrounding tissue).^2,3 These conditions are typically considered to exist on a continuum and are common in dogs, with a reported incidence ranging from 4.4% to 15.7% in primary care practices.^2-4

Anal sacculitis accounts for approximately 12% of all NASDs.⁴ Several factors, including allergic skin disease, breed, stool quality, diet type and changes, obesity, and other perianal skin diseases, are suggested to play a role in the development of anal sacculitis.^3-7 However, few studies investigating the etiology of anal sacculitis exist.

Allergic Skin Disease

In 2 retrospective studies, allergic skin disease—specifically atopic dermatitis caused by food and/or environmental triggers—was identified as the most common comorbidity for dogs with anal sacculitis.^5,7 This is consistent with the view that allergic skin disease can lead to perianal inflammation, contributing to anal sac duct stenosis, impaction, and ultimately anal sacculitis.⁴ However, due to the retrospective nature of these studies, while a relationship is suggested, true causation is not confirmed. Interestingly, a recent study using bacterial 16S rRNA gene sequencing found that there was a significant difference in the bacterial microbiota between the anal sacs of healthy and untreated atopic dogs as well as between treated and untreated atopic dogs.⁸ This indicates that atopic dogs experience anal sac dysbiosis, which may predispose them to the development of anal sacculitis.⁸

Breed

Breed may also play a role in the development of anal sacculitis. In a study investigating the development of NASD, a strong predisposition was found for spaniel and brachycephalic breeds.⁴ This predisposition may not directly translate to anal sacculitis predisposition specifically. Two retrospective studies focusing on anal sacculitis found German shepherds and Labrador retrievers to be the 2 most highly represented breeds; these breeds were the most represented by narrow margins, and true risk has not been established.^5,7 At this time, it is uncertain how much a role breed plays in the development of anal sacculitis; in the authors’ experience, it can occur in a wide variety of breeds.

Stool Quality And Diet

One study identified a history of diarrhea prior to the development of clinical signs of anal sacculitis in 75% of cases.⁶ Of these dogs, 75% were fed either all-meat diets or diets containing chop bones and had a history of either poor stool quality or rectal impaction.⁶ In contrast, a more recent retrospective study found that only 20.6% of dogs with anal sacculitis had poor stool quality.⁵ This difference may be explained by the fact that most dogs in the second study were fed commercially available dog food. However, the latter study was performed at a dermatology referral practice, where there was a delay between onset of signs related to anal sacculitis and presentation to the clinic, meaning some cases of poor stool quality prior to development of anal sacculitis may not have been captured.⁵ While stool quality may be involved in the development of anal sacculitis for some individuals, it is not a consistent finding.

Obesity

Obesity has also been reported to be implicated in the development of anal sacculitis.² However, a large retrospective study of dogs in the United Kingdom found no association between obesity and NASD.⁴ When dogs are evaluated for obesity, a body condition score (BCS) ranging from 1 to 9, with an ideal of 4 to 5, is commonly used.⁹ Looking specifically at anal sacculitis, a retrospective study of dogs in Sweden found that 63.6% had an ideal BCS of 5 and 36.3% were slightly overweight with a BCS of 6.⁷ All dogs were scored at either a 5 or 6.⁷ In a retrospective study on dogs with anal sacculitis in the United States, 45.2% had an ideal BCS of 4 or 5.⁵ The remaining 54.8% of dogs were overweight with a BCS of greater than 6, and 9.7% were obese with a BCS of 8 or 9.⁵ Based on these results, it is still uncertain how much of a role obesity plays in the development of anal sacculitis, although it may be less than previously thought.

Diagnosis

Clinical signs associated with anal sacculitis include scooting, licking/chewing the perianal region, blood in the stool, and/or leaking anal sacs.⁵ Affected animals may present with 1 or a combination of these clinical signs. On rectal examination, the anal sac wall may be diffusely thickened and there may be hemorrhagic to purulent discharge present upon anal sac expression.^5,6 Cytologic findings from the material of clinically normal and affected canine anal sacs are reported to be highly variable.^10-13 Although controversial, the presence of moderate to large numbers of erythrocytes with or without moderate to large numbers of inflammatory cells and coccoid and/or  rods or yeast on cytology may be used to support the diagnosis of anal sacculitis when combined with the history and clinical assessment.^10-12

Treatment

Many protocols for treatment of anal sacculitis have been proposed. Although systemic antibiotics have commonly been prescribed for cases of anal sacculitis, there is evidence that localized treatment is becoming more popular, with 1 study finding that 73.1% of dogs with anal sacculitis in a primary care practice in Sweden were treated with localized treatment, with or without systemic NSAIDs, and an additional 13.5% received local treatment with a systemic immunomodulatory medication, with or without systemic NSAIDs.⁷ In the study performed at a U.S. dermatology referral center, 54.5% of dogs had been prescribed at least 1 course of antibiotics prior to presentation, without full resolution of the problem.⁵ With the increasing incidence of antibiotic resistance, a focus on localized treatment improves antimicrobial stewardship because it reduces the use of systemic antibiotics.

A published protocol for localized treatment of canine anal sacculitis involves⁵:

1. The digital expression of the anal sac (FIGURE 1)
2. Careful insertion of a lubricated intravenous catheter sheath or shortened 3.5-French Tom Cat catheter into the anal sac duct (FIGURE 2)
3. Flushing of the anal sac with saline until all anal sac material is removed (FIGURE 2)
4. Infusion of a commercially available antibiotic, antifungal, and glucocorticoid otic ointment such as Mometamax Otic Suspension (Merck Animal Health, merck-animal-health-usa.com) into the anal sac until the sac is full (extra-label use)

FIGURE 1. The white arrows indicate the location of the opening of the anal sac ducts. Providing external rotation during digital palpation may be required for better visualization of openings.

Figure 2. Following digital anal sac expression, a lubricated intravenous catheter sheath or shortened Tom Cat catheter is carefully inserted into the anal sac duct and the sac is flushed with sterile saline until all material is removed from within the sac.

Sedation is typically required to perform this procedure.⁵ The procedure should be repeated at approximately 2-week intervals—potentially multiple times—until remission is achieved.^5,7

In a retrospective study performed at a primary care practice in Sweden, there were a median of 2 visits per anal sacculitis episode.⁷ At a U.S. dermatology referral practice, an average of 2.9 treatments were performed prior to anal sacculitis resolution.⁵ For the latter study, many of the patients had chronic anal sacculitis, which may be more difficult to treat than acute anal sacculitis. Nevertheless, this study, which used localized anal sacculitis treatment in 33 dogs, found that 72.7% of cases achieved clinical resolution as determined by a veterinarian. An additional 12.1% were reported to have resolution by the dog’s owner without confirmation from a veterinarian. The remaining 15.2% of cases did not complete the recommended follow-up, and no data were available on whether they achieved resolution. No cases were documented to have failed medical therapy.

While the factors involved in the development of anal sacculitis are not definitively identified, it is typically considered a secondary condition with possible recurrence. In the study on dogs with anal sacculitis in a primary care practice in Sweden, 33.7% of dogs experienced at least 1 episode of recurrence of anal sacculitis with a range of time to recurrence from approximately 1 month to 3 years.⁷ Dogs with allergic skin disease had a significantly higher risk of recurrence, with 46.6% of these dogs experiencing at least 1 episode of recurrence.⁷ In the study on anal sacculitis treatment in a U.S. dermatology referral practice, anal sacculitis recurrence was seen in 10.7% of dogs, occurring anywhere from 85 to 445 days after initial resolution.⁵ For 2 of these dogs, the factors contributing to the development of anal sacculitis were unknown.⁵ One of the dogs experienced recurrence approximately 1 year after first being treated, and seasonal atopic dermatitis was thought to contribute to the development of anal sacculitis.⁵ All 3 dogs achieved resolution with a second round of treatment.⁵ Although a direct comparison cannot be made between these studies, differences in the level of control of allergic skin disease may contribute to differences in recurrence rates.

Anal sacculectomy has also been used for the treatment of anal sacculitis; however, it can result in long-term complications, such as fecal incontinence and anal stricture.^4,14 No dogs in the U.S. retrospective study required surgery.⁵ In the retrospective study performed in Sweden, anal sacculectomy was performed in approximately 5% of dogs that were initially treated medically, but an inconsistent treatment protocol was applied at each visit.⁷ Clinical remission was achieved in all dogs for which a consistent treatment protocol was used.⁷ Therefore, based on the high success rate reported with localized treatment and control of possible contributing factors, anal sacculectomy should be reserved for cases of anal sac neoplasia and those cases that fail appropriate medical therapy.

Summary

Anal sacculitis is a subset of NASD. It is a relatively common disease in dogs that can negatively impact quality of life. The clinical presentation of this condition is heterogenous. Anal sacculitis is typically considered secondary to other conditions or risk factors. However, little evidence exists to suggest a link between anal sacculitis and conditions other than allergic skin disease.^5,7 Further research is needed to investigate the association between anal sacculitis and various diseases, in addition to the potential risk factors for development of this condition. Localized treatment for anal sacculitis has been considered an effective alternative to systemic antibiotic therapy for some time, and results of recent retrospective studies support the efficacy of this treatment approach, which can improve antimicrobial stewardship practices.^5,7