5 vile veterinary derm conditions that get under my skin

Though working in veterinary dermatology is a daily assault on the senses, I find the grossest of diseases to be the most rewarding to treat, as they greatly improve the quality of life for the patient and the client while restoring and strengthening the human-animal bond (since most of us like to be near our pets without gagging). Here are five of the most cringe worthy dermatologic conditions I've encountered:

Perianal fistula

Alias: Anal furunculosis

Description: Perianal fistula is a chronic, progressive inflammatory disease that's most often diagnosed in middle-aged German shepherds. The etiopathogenesis is only partially understood, but genetic and anatomic factors and a dysregulated immune response are known disease contributors.

Signs: Dogs often present with perianal licking, tenesmus, painful defecation, weight loss and lethargy. The perianal lesions are not associated with the anal sacs and can range from pinpoint-sized draining tracts to large, cavitating, ulcerated sinuses. Upon palpitation, the anus and rectum may be thickened and fibrous, and a malodorous mucopurulent discharge is often present. Because about half of affected individuals have concurrent colitis, it can be assumed that the scope of the disease extends beyond external lesions.

Diagnostics: Diagnosis is based on the patient's history and on clinical findings.

Treatment: Treatment involves systemic cyclosporine (5 to 10 mg/kg/day) and topical 0.1% tacrolimus ointment. Systemic antibiotics are initially needed to treat the secondary bacterial infection, and concurrent prednisone can be used to reduce inflammation at presentation. If the pet doesn't demonstrate a complete response to initial therapy, a diet trial may be needed to rule out concurrent cutaneous adverse food reactions.

Mycobacterial panniculitis

Alias: Atypical mycobacterial granulomas

Description: Mycobacteria are ubiquitous, saprophytic organisms that can cause problems when the skin's barrier is compromised and they are given access to the fatty subcutis. Obese outdoor cats may be more predisposed to disease development.

Signs: Opportunistic mycobacteriosis often presents as chronic, nonhealing wounds. The lesions may initially resemble catfight abscesses and are most commonly seen along the caudal abdominal or inguinal regions or the lumbar region (though they can be present anywhere). The areas develop circumscribed plaques or nodules and progress to underlying thickening of the subcutis and the development of punctuate fistulae that discharge watery, bloody exudate.

Diagnostics: The disease can be difficult to diagnose. Acid-fast stains are necessary to detect the elusive organisms obtained via fine-needle aspiration of closed lesions. Dermatohistopathology demonstrates nodular to diffuse pyogranulomatous dermatitis and panniculitis, but additional stains are recommended to identify organisms. Mycobacterial tissue culture can take longer than typical bacterial cultures.

Treatment: Treatment is often frustrating for both the client and the veterinarian. Systemic antimicrobial therapy is often needed for a long period of time (three to 12 months) and is then extended one to two months past clinical resolution. Antimicrobial selection should be made based on the mycobacterial culture's susceptibility tests. Combination therapy is often needed, and some cases require surgical excision to debride the affected tissues.  

Pemphigus foliaceus

Description: Pemphigus foliaceus is the most common cutaneous autoimmune disease in dogs and cats. Any age, sex or breed can be affected, but Akitas and chow chows may be predisposed. The disease is characterized by the production of antibodies that attack the adhesion molecules of keratinocytes.

Signs: The primary lesions of this disease are large, superficial pustules that span multiple follicular units. These pustules rupture easily, so patients often present with crusted erosions and alopecia. Nasal planum, ear pinnae and periocular tissues are often affected, but generalized disease may also occur.  In cats, claw folds are frequently affected, and thick caseous exudate can be detected when the claws are extracted. Pets can also be systemically ill and present with depression, anorexia and fever.

Diagnostics: Acantholytic cells (the large, round keratinocytes) can be detected with cutaneous cytology and dermatohistopathology. When obtaining a tissue biopsy, it is vital to include any crusts, if present.

Treatment: Immunosuppression is the cornerstone of therapy. Corticosteroids, prednisone or prednisolone should be initiated. Some cases may require additional therapy using other immunosuppressive medications to achieve adequate control. 

Pseudomonas otitis externa

Description:Pseudomonas aeruginosa is a common finding in treatment-resistant canine ear infections. Pseudomonas is considered opportunistic bacteria that overgrows in a diseased ear canal, often when normal flora has been inhibited by antimicrobial therapy. 

Signs: These patients often have significant erosion and ulceration along the ear canal walls that can be very painful. This process is often accompanied by a noticeable odor.

Diagnostics:Pseudomonas ear infections tend to produce copious amounts of purulent exudate, which demonstrate large bacilli and numerous leukocytes on cytology.

Treatment: Treatment can be frustrating for clients and clinicians, as P. aeruginosa has demonstrated the ability to produce biofilms, which correlate with reduced topical antimicrobial efficacy. Irrigation and cleaning of the canals are imperative in these cases. Patients also benefit from topical and systemic glucocorticoids. Bacterial ear infections are considered a secondary cause of otitis externa. Allergies, foreign bodies and parasites are all potential primary triggers for ear disease. The ear infections will continue to return if the primary abnormality is not addressed.

Necrolytic migratory erythema

Aliases: Metabolic epidermal necrosis, hepatocutaneous syndrome, superficial necrolytic dermatitis

Description: Several names have been given to this disease process, which has been described in people, dogs and cats as being associated with liver disease or a glucagon-secreting pancreatitis tumor. The exact pathogenesis is unknown, but it has been proposed that degeneration of keratinocytes is triggered by cellular starvation or other nutrition imbalance. Patients often present with hypoaminoacidemia resulting from hyperglucagonemia, liver dysfunction or malabsorption. It is often seen in older animals, and the cutaneous signs may present prior to systemic illness.

Signs: Skin lesions often present in areas of trauma, especially the muzzle, mucocutaneous junctions, distal limbs and paw pads. Scaling, crusting, erosions and ulcers characterize these areas. The paw pads may demonstrate hyperkeratosis with fissuring and ulceration. Secondary bacterial infections are often present.

Diagnostics: Diagnosis is often achieved with dermatohistopathology. Abdominal ultrasound may reveal a honeycomb pattern (hyperechoic, reticular pattern surrounding hypoechoic areas).  

Treatment: Prognosis for these cases is poor, but treatment with parenteral amino acids may improve the skin lesions and prolong survival time.

Melissa Hall, DVM, DACVD, is a veterinary dermatologist at the Animal Dermatology Clinic in Tustin, California.