Anal Sac Abscess in a Dog with Suspected Adverse Food Reaction

Canela, a 5.5-lb (2.5-kg) spayed Chihuahua, was presented to a referral clinic for a 1-year history of recurrent anal sac impaction, anal sacculitis, and facial pruritus. Her condition worsened (including reduced activity and inappetence) 2 days prior to presentation. She demonstrated a kyphotic posture and strained to defecate the day prior to presentation.

Perianal pruritus was 8/10 on a scale of 1 to 10, with 10 being the most pruritic. Facial pruritus was 4/10. Canela dragged her perianal region across the floor frequently and was painful when the perianal area was examined. She appeared otherwise healthy.

Anal sac impaction was previously treated with prednisone (0.5 mg/kg PO every 24 hours for 7-10 days), anal sac expression (weekly), and addition of pumpkin puree to the diet with poor clinical response. Anal sacculitis subsequently developed twice over a period of 6 months, and amoxicillin/clavulanic acid (13.75 mg/kg PO every 12 hours for 7-10 days) was prescribed. The final treatment for anal sacculitis was prescribed 3 months before presentation to the referral clinic.

Physical Examination

On physical examination at the referral clinic, Canela was bright and alert with a slightly elevated body temperature (102.5°F [39.2°C]). Examination revealed severe erythema and bruising localized to the perianal area and ventral aspect of the tail, as well as a focal area (≈1 cm) of erosion-to-ulceration with a draining tract associated with the left anal sac, from which serosanguinous content was expressed (Figure 1). The right anal sac was full on external palpation, and Canela was reactive to palpation of the affected area.

FIGURE 1

Anal sac abscess with fistulation; surrounding skin is bruised and swollen.

Diagnosis

Differential diagnoses for perianal swelling with an associated draining tract include anal sacculitis/abscessation with fistulation, neoplasia, and perianal fistulas.

Canela was sedated so the draining tract could be explored further. The area was shaved, and a sterile 20-gauge catheter tip was inserted to facilitate communication with the left anal sac. The area was copiously flushed with sterile saline, and a thick fibrinous material was removed from the anal sac. A sample was collected for cytologic evaluation; results revealed neutrophilic inflammation with mild lymphocytic and eosinophilic inflammation. A moderate number of intra- and extracellular cocci bacteria were also observed. The skin adjacent to the fistula was bruised, swollen, and apparently sensitive to touch, suggestive of cellulitis. The right anal sac was expressed, and a soft tan-colored material was obtained.

Diagnosis: Left Anal Sac Abscess with Fistulation & Suspected Allergic Dermatitis

Treatment & Management

Amoxicillin/clavulanic acid (13.75 mg/kg PO every 12 hours for 14 days) and meloxicam (0.1 mg/kg PO every 24 hours for 5 days) were prescribed after the affected anal sac was flushed. Although a systemic antibiotic was used in this case because of the presence of cellulitis, draining, flushing, and infusing with an antiseptic/anti-inflammatory ointment may be effective for uncomplicated cases (see Treatment at a Glance).

Because atopic dermatitis is a common comorbidity associated with anal sacculitis and Canela had a history of facial pruritus, a food elimination trial with a limited-ingredient diet was recommended to investigate food-induced atopic dermatitis.

Prognosis & Outcome

Canela showed significant improvement at the 2-week recheck. The anal sac fistula was healed; there was a small crust at the site of previous fistula; and no inflammation was present in the previously affected area.

At the 4-week recheck, facial pruritus was decreased (1-2/10). A therapeutic diet limited to kangaroo and potato was being fed. The food elimination trial was continued for an additional 4 weeks, after which facial pruritus was resolved and there was no recurrence of anal sac disease. The owner elected to not challenge Canela with the previous diet; adverse food reaction could thus not be confirmed. In a recent study of 46 dogs with suspected adverse food reaction; 60.9% of dogs developed pruritus within 12 hours of food challenge, and pruritus developed within days in only a few dogs.¹

Canela was free of clinical signs at the 3-month follow up.

Continuous monitoring was recommended because recurrence of nonneoplastic anal sac disease is frequent in patients with no identifiable underlying cause or uncontrolled comorbidities. One study indicated an 81% recurrence rate of clinical signs in patients with anal sac impaction within 3 weeks of anal sac expression.² Frequent expression may be needed for predisposed patients.

Discussion

Nonneoplastic anal sac disease is relatively common (incidence, 2%-12.5%) in dogs and can include impaction, sacculitis, abscessation, and fistulation.³

Impaction occurs when the anal sac fails to empty and is commonly associated with thickened content and plugging of the anal sac duct. Sacculitis is associated with a secondary infection of the anal sacs, which can result in abscessation (Figure 2) and fistulation (Figure 3).⁴

FIGURE 2

Anal sac abscess in a 3-year-old cocker spaniel/poodle crossbreed

FIGURE 3

Anal sac abscess with fistulation in a 5-year-old crossbreed dog

Dogs affected with anal sac impaction often drag, lick, and bite the perianal region, causing self-trauma and perianal dermatitis. Anal sacculitis, abscessation, and secondary cellulitis are possible in more severe cases.²

A retrospective study found that Cavalier King Charles spaniels, English toy spaniels, cocker spaniel/poodle crossbreeds, shih tzus, bichons frises, and cocker spaniels have a higher risk for developing anal sac disease and brachycephalic breeds are 2.6 times more likely than dolichocephalic breeds to develop anal sac disease.⁵ Chihuahuas and miniature poodles are predisposed to anal sacculitis.⁶

Color and consistency of canine anal sac secretion varies significantly. Cytologic evaluation findings are also variable; however, presence of blood and intracellular bacteria should be investigated, as these are not normal and can indicate infection.⁷

Atopic dermatitis was the most common comorbid condition associated with nonneoplastic anal sac disease in a study evaluating topical flushing and treatment.⁸ Other underlying conditions or predisposing factors previously reported include stool quality, obesity, small anal sac duct, diet, and skin disease.⁴

Management with antibiotics and pain medications is most common; anal sacculectomy is performed in <1% of cases. Possible complications of anal sacculectomy include perianal cellulitis, fistulation, excessive drainage from the incision site, and fecal incontinence, which is uncommon but possible because of the close association between anal sacs and the external anal sphincter muscle and caudal rectal nerves. Small dogs (<33 lb [15 kg]) are at increased risk for postoperative complications.⁹

Listen to the Podcast

Listen to Dr. Diaz dive deeper into the frustrating and multifactorial problem of anal sac disease with a focus on possible underlying causes and perpetuating factors.