Draining sinus tracts 1

Question 1

What is a sinus?

Answer 1

= tract from skin surface to a deeper, but abnormal, focus, usually in the dermis or subcutis

Question 2

What is a fistula?

Answer 2

= tract between two epithelium-lined structures (e.g. skin and a hollow organ)

Question 3

2 fistulae seen in dermatology

Answer 3

• Anal furunculosis – sometimes referred to (inaccurately) as ‘perianal fistulae’ - actually are sinuses
• Fistulae of the feet – tract between the dorsal and palmoplantar aspects of the foot

Question 4

Why do sinus tracts usually form?

Answer 4

• due to an attempt to reject material from dermis or subcutis

Material sets up an inflammatory/foreign body reaction → bulla → ruptures → draining tract

Question 5

How does material reach the dermis/subcutis? (i.e. different types of sinus tracts)

Answer 5

• Penetration from surface
  – e.g. foreign body, mycobacterial/ opportunistic fungal infections
• Breakdown of the hair follicle (furunculosis), e.g.
  – deep pyoderma
  – demodicosis
  – dermatophytosis
• Systemic routes
  – e.g. systemic mycoses
• Formed within skin
  –e.g. immune-mediated/autoimmune

Question 6

What do draining tracts usually reflect?

Answer 6

▪ Deep infection
▪ Foreign body
▪ Immune-mediated/autoimmune disease

Question 7

Non-infectious causes of draining sinus tracts

Answer 7

Immune-mediated/autoimmune
- Anal furunculosis (perianal fistulae)
- Metatarsal fistulation
- Sterile panniculitis (inflammation of s/c fat, with no underlying infectious cause)
▪ Steatitis (‘yellow fat disease’)
▪ Sterile nodular panniculitis
- Dermoid sinus

Question 8

General investigative approach to draining sinus tracts

Answer 8

Signalment, history, clinical examination ▪ Site of lesion
▪ Solitary/multifocal
▪ Palpable underlying nodule?
▪ Nature of exudate
▪ Lifestyle of patient
▪ Other clinical signs (dermatologic/systemic)

Question 9

Diagnosis

Answer 9

▪ Cytology of exudate
▪ Deep skin scrapes/hair plucks
▪ Biopsy for histopathology and tissue culture – frequently required
▪ Microbial culture
▪ Other tests, as indicated
– E.g. Serology (leishmaniasis, sporotrichosis), fluorescent in situ hybridization for microbes

Question 10

Diagnosis - Cytology of exudate

Answer 10

▪ FNA from bulla, if present
▪ Touch impression of sinus tract contents

Often pyogranulomatous/granulomatous. May see organisms (Diff Quick + Gram if possible)

Question 11

Diagnosis - Deep skin scrapes/hair plucks

Answer 11

• if demodicosis suspected

Question 12

Diagnosis - Biopsy for histopathology and tissue culture

Answer 12

• Do not shave or cleanse first
• Biopsy erythematous skin adjacent to tract and go deep enough to include dermis and subcutis–need wedge, not punch. Multiple samples/locations.
• May need special stains( e.g. for mycobacteria, Actinomyces, Nocardia, fungi)– notify pathologist of your d/ds

Question 13

Diagnosis - Microbial culture

Answer 13

▪ Tissue culture best – tissue with drop of sterile saline in sterile universal container
▪ If tissue grains present in exudate, submit for culture also – often many organisms
▪ Swabs in transport media?
– more prone to contamination – best from FNA of bulla or deep in sinus tract ▪ Request
– Aerobic + anaerobic bacterial culture
– Fungal culture (not just dermatophytes)
NB Notify lab of d/ds – re safety and selection of appropriate culture requirements

Other points
▪ If unsure whether culture needed, chill or freeze additional deep tissue samples (not in formalin!)
pending histopathology results → microbial isolation later, if needed
▪ Freeze fresh tissue samples when submitting biopsies for histopathology from any cutaneous/subcutaneous mass in a cat
– Mycobacteria very hard/slow to grow - can do mycobacterial PCR on fresh frozen tissue

Question 14

Anal furunculosis - Aetiology & pathogenesis

Answer 14

• The cause is unknown but is suspected to involve an immune-mediated mechanism with a genetic predisposition
• A broad-based tail with low tail carriage may predispose to bacterial infection and chronic inflammation of the perianal skin, but this is likely a contributing factor and not a cause
• The draining tracts are lined with chronic inflammatory tissue and may extend to the lumen of the rectum and anus
• Infection may spread to deeper structures involving the external anal sphincter and, therefore, should be treated promptly.

Question 15

Anal furunculosis - CS

Answer 15

• tenesmus
• dyschezia
• diarrhea
• constipation
• fecal incontinence
• purulent discharge from the perianal region

Discomfort caused by the condition may lead to biting and licking of the perianal region.
Pain may also cause generalised depression or change in attitude and anorexia.
As the condition becomes chronic, anorectal stricture may result.

Question 16

Anal furunculosis - diagnosis

Answer 16

• Based on physical examination and ruling out other causes of the signs
• In addition to the signalment and history, physical examination, including digital rectal examination, is a primary means of diagnosis
• Other causes of fistulisation (eg, anal sac disease, neoplasia) need to be ruled out
• Bacterial culture to identify organisms causing secondary infection may be needed
• Tissue biopsy is rarely indicated.

Question 17

Anal furunculosis - tx

Answer 17

• Cyclosporine is the treatment of choice

Medical management is the primary mode of treatment. Cyclosporine (2–10 mg/kg, PO, every 12–24 hours, with monitoring) is the medication of choice. Higher dosages may be associated with improved outcome. After complete resolution of lesions (usually 8–12 weeks), cyclosporine is tapered to the least-effective dose that prevents relapse, which is common after stopping therapy. The concurrent use of ketoconazole allows for a lower dosage of cyclosporine and may reduce the cost of treatment.

Tacrolimus (0.1% ointment applied topically once or twice daily) may be used to treat mild lesions or as long term management after resolution of more severe lesions. Antimicrobials may be needed to treat secondary infections but are not effective as the primary or sole therapy for perianal fistulas.

Stool softeners and analgesics may be beneficial in dogs with significant tenesmus, dyschezia, or constipation.

Whereas once the mainstay of therapy, surgery is typically reserved only for cases refractory to medical management. Potential procedures include en bloc excision, anal sacculectomy, cryosurgery, and tail amputation. Complications of surgery can include wound dehiscence, fecal incontinence, anal stricture, persistence of clinical signs, and recurrence of fistulas.

Question 18

Anal furunculosis - primary breed it affects

Answer 18

GSD

Question 19

Pansteatitis - cause

Answer 19

• Vitamin E deficiency and/or excessive dietary unsaturated fatty acids
• The inadequate vitamin E:unsaturated fatty acid ratio results in oxidative damage to adipocytes and subsequent lipid peroxidation.
• Cats that eat a fish only diet are at increased risk of developing this disease
• Other unbalanced, meat-based diets have also been implicated in the development of pansteatitis.

Question 20

Pansteatitis - CS & clinical features

Answer 20

• Clinical signs include subcutaneous nodules, draining tracts, lethargy, inappetence, fever, pain and reluctance to move
• Haematological abnormalities may also be present
• Affected adipose tissue has an unusual yellow–orange colour.

Question 21

Pansteatitis - diagnosis

Answer 21

• The dietary history and clinical signs will strongly suggest pansteatitis
• However, a skin biopsy (being careful to include adipose tissue in the biopsy) with special stains for infectious agents is necessary to confirm the diagnosis and rule out infectious causes of inflammation of the fat
• Plasma tocopherol levels of <300 mg/100 ml further confirm the diagnosis.

Question 22

Pansteatitis - tx

Answer 22

• Affected cats should receive supportive care including pain medication and parenteral fluid therapy, depending on the severity of their condition
• Affected cats should be fed a high-quality, ­ properly balanced diet
• Additional α -tocopherol supplementation (50 mg/kg po q24 h) may also be helpful to speed recovery
• Full recovery may take several weeks
  -mIt is imperative that affected cats continue to consume a balanced diet even after resolution of clinical signs.

Question 23

Pansteatitis - how it affects multicat households

Answer 23

• Cats have different abilities to tolerate diets high in unsaturated fatty acids and/or deficient in vitamin E
• Some cats will develop pansteatitis and others will not even when fed the same diet

Question 24

Metatarsal fistulation - definition

Answer 24

= an uncommon condition where draining tracts occur in the skin of the plantar metatarsal area

Question 25

Metatarsal fistulation - aetiology & pathogenesis

Answer 25

• pathogenesis is unknown
• but circulating antibodies to types I and II collagen were elevated in some affected dogs

Question 26

Metatarsal fistulation - clinical features

Answer 26

• found in German Shepherd dogs (GSDs), crossbreeds of GSDs and occasionally other breeds
• Initial lesions consist of a soft swelling in the skin, which progress to well-demarcated single or multiple tracts containing a serosanguineous discharge located on the plantar metatarsal skin surface, just proximal to the metatarsal pad
• Both hindlimbs are affected and occasionally lesions occur in the plantar metacarpal skin
• Secondary bacterial infection can occur once sinus tracts develop
• The affected skin of chronic lesions may become scarred
• Pain is variable, but appears to be mild in most dogs.

Question 27

Metatarsal fistulation - ddx

Answer 27

Not many differentials with bilaterally symmetrical disease with no systemic signs, but if asymmetrical or the pet is sick, consider:
- Foreign body
- Puncture wound
- Subcutaneous mycosis such as blastomycosis
- Deep bacterial infection such as actinomycosis

Question 28

Metatarsal fistulation - diagnosis

Answer 28

• Any case with fever or changes on blood work should have infectious causes more aggressively ruled out
• When this disease is suspected, cytology, bacterial culture and biopsy with special stains to rule out other causes should be considered before empirical treatment.

Question 29

Metatarsal fistulation - tx

Answer 29

• Modified ciclosporin 5 mg/kg per day is the treatment of choice.
• Other options include topical 0.1% tacrolimus q12 h, topical fluocinolone/DMSO, prednisolone at 1 mg/kg per day and then tapered, 3 doxycycline or minocycline and niacinamide, or vitamin E.