Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA
When the word “emergency” is spoken, dermatologic conditions are not the first ones that come to mind. Nonetheless, there are a number of rather serious and life-threatening conditions that can manifest entirely or partially on the skin. The purpose of this lecture is to discuss a few of these conditions.
Erythema Multiforme/Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis
These conditions are immune-mediated disorders that may manifest in the skin, mucocutaneous junctions and mucous membranes. In humans, the clinical and etiologic differences between these syndromes are fairly well defined. Characterization and differentiation of the syndromes is less well defined and somewhat controversial in the dog, and considerable overlap between the three conditions may be seen.
Erythema multiforme (EM) is typically characterized by the development of erythematous macules, papules or raised circular, serpiginous or arc-shaped plaques. Vesicles, bullae or ulcers may be seen but are typically not the predominant lesion. One or more mucosal surfaces may be affected.
Stevens Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) typically appear as erythematous macules and patches, which subsequently develop areas of epidermal detachment. The two syndromes differ primarily with regards to the extent of the lesions, with SJS typically involving <10% of the body surface area, TEN involving >30% of the body surface area and an SJS/TEN overlap involving between 10–30% of the body surface. Mucous membranes and footpads are commonly involved. Patients are often systemically ill.
Because there is a lack of consensus with regards to the exact definition of these syndromes in veterinary medicine, the identity of potential triggering factors is poorly defined. In many (and perhaps the majority) of cases, no clear trigger can be identified. Other putative triggers include drug administration. neoplasia, infections. vaccinations, and dietary items. Drug administration is more likely to represent a trigger for SJS/TEN than it is for EM.
Differential diagnoses would include exfoliative staphylococcal pyoderma, eosinophilic dermatitis/Wells syndrome, sterile neutrophilic dermatitis (Sweet’s syndrome) and cutaneous lymphoma. A thorough history must be obtained, focusing on the administration of recent medications (including vaccines, heartworm and flea preventatives), exposure to other animals with infectious diseases and/or presence of signs consistent with infectious disease. Skin scrapings, bacterial and dermatophyte cultures may be appropriate to rule out other differentials. Bloodwork (complete blood count, chemistry profile, urinalysis) is appropriate both to determine the extent of systemic involvement and to provide a reference for therapeutic monitoring. Thoracic and abdominal imaging may be appropriate to investigate the potential for neoplasia. Skin biopsy will be important to support the clinical diagnosis, although the practitioner must be aware that there may be considerable histologic overlap between the two conditions.
Therapy for these conditions is mostly supportive, including analgesic therapy, fluids and nutritional support. The prophylactic use of systemic antibiotics is somewhat controversial and likely should be avoided except in cases of severe epidermal loss. If a drug reaction is suspected, all drugs not essential for life should be promptly discontinued.
Topical therapy plays an important role in management. Frequent cleansing with gentle antiseptic products is an appropriate approach to the prevention of infection. Patients with extensive erosion or serum oozing may benefit from gentle hydrotherapy or whirlpool treatment to help remove surface debris and bacteria. A light application of topical antimicrobial agents (such as silver sulfadiazine) may be helpful, but care must be taken to avoid over application, which will result in maceration of the skin.
In severe cases, immunosuppressive therapy may be indicated. The most frequently used medications are glucocorticoids (prednisolone 2.2 mg/kg per day), but adjunctive medications may also be added. These include cyclosporine (5 mg/kg once daily) or mycophenolate mofetil (10 mg/kg twice daily). Intravenous administration of human immunoglobulin (IVIG; 0.4–0.5 g/kg [5% solution] IV once over 4–8 hours) has been reported to be effective in some cases, including one managed at the author’s institution. The prognosis depends upon a number of factors, including ability to identify (and address) the inciting cause, and the extent of the condition. Patients with extensive epithelial loss are predisposed to the development of secondary infection and sepsis.
In cases demonstrating persistent lesions, a food allergy elimination diet trial may be indicated to rule out food associated EM.
Juvenile Cellulitis (Puppy Strangles)
This is an idiopathic inflammatory condition of young dogs. There is evidence suggesting both a genetic (Labrador Retriever, Dachshund, Pointer and Beagles may be predisposed) and immune mediated components (the condition is glucocorticoid responsive, and may closely follow vaccination).
The condition typically appears in puppies <6 months of age, but it may occasionally appear in young adults. The condition may appear shortly (days to 1–2 weeks) after vaccination. Affected puppies develop a sudden onset of facial and pinnal swelling. The affected areas rapidly develop short-lived vesicles or pustules, particularly on the lips, eyelid margins and on the concave surface of the pinnae. These vesicles rupture to leave crusting and erosions, which may exude serous or serosanguinous discharge. Pinnae are often markedly edematous, with erosion extending to the canal. Secondary otitis externa is common. Lymph nodes (especially the submandibular and prescapular nodes) are often markedly enlarged and painful. The skin overlying the nodes is often ulcerated and draining. Patients may have one or more body regions affected. Puppies are often depressed (sometimes severely so), and may express pain upon opening the mouth.
Differential diagnoses include angioedema, demodicosis with secondary infection, drug reactions, bacterial furunculosis/abscessation and caustic substance exposure. Deep skin scrapings should be negative. Cytology of fresh lesions should demonstrate purulent to pyogranulomatous inflammation. Culture obtained from fresh lesions should be negative but some bacteria may be seen if secondary infection is present. Biopsy of fresh lesions should demonstrate a sterile pyogranulomatous infiltrate in the deep dermis and subcutis.
Patients typically respond well to immunosuppressive doses of glucocorticoids. Glucocorticoid therapy should be continued until the lesions are completely in remission. Although the lesions are usually sterile, adjunctive antibiotic therapy is prudent in cases with significant ulceration. Gentle daily cleansing with an antiseptic solution is appropriate if practical. Patients may require adjunctive analgesic therapy. Nonsteroidal antiinflammatory drugs are not appropriate in conjunction with glucocorticoids, so alternative medications such as tramadol should be used. Most patients demonstrate improvement within a week or so, although individuals may require several weeks for full improvement. The author has seen one particularly severely affected case which was quite systemically ill, failed to respond and died despite therapy. If vaccination is thought to be an inciting cause, it may be prudent to minimize and/or spread out future vaccinations.
This is an uncommon but not rare condition in which deep bacterial infection appears to develop subsequent to bathing or immersion in water, although a single case has been reported in which the lesions appeared after scrubbing the skin in preparation for a hemilaminectomy. Patients may have been bathed at home or at a professional grooming parlor. One case was reported following a therapy session on an underwater treadmill. It is thought that the combination of exposure to contaminated water, shampoo or scrub solution along with the physical act of scrubbing causes microtrauma to the skin and follicles and introduces microbes deep into the dermis.
Signs typically follow closely (average 2 days) after the inciting event. Patients often present first for pain over the dorsum. The discomfort may be severe enough to mimic trauma or disk herniation. Within one or two days, patients typically develop a papular eruption on the dorsum, which quickly evolves into furuncles and deep draining tracts. Patients may become depressed with evidence of systemic involvement or may appear otherwise well.
The peracute appearance of dorsally distributed pain followed by the rapid development of furuncles in a patient with a history of recent bathing or water exposure is extremely suggestive. Differential diagnoses would include disk herniation or spinal trauma (if seen before the cutaneous lesions develop), demodicosis, pustular dermatophytosis, drug eruption, SJS/TEN and chemical or thermal burns. In contrast to “typical” bacterial furunculosis, the causative organism here is typically Pseudomonas aeruginosa, although other organisms may also be present. Cytology may demonstrate gram-negative bacteria, with or without concurrent gram positive cocci. Skin scrapings and dermatophyte cultures will be negative. Biopsy will demonstrate furunculosis and cellulitis, with or without intralesional bacteria.
Prompt aggressive analgesic and antibiotic therapy (typically with fluoroquinolones) is absolutely essential. Severely affected animals may require hospitalization and more advanced supportive fluid therapy. A complete blood count, chemistry profile and urinalysis are appropriate, both to evaluate for possible systemic involvement and to provide a baseline for therapeutic monitoring. Blood cultures may be warranted in severely affected animals.
The prognosis for post-grooming furunculosis is generally considered to be very good, with most animals demonstrating improvement within 24–48 hours. However, individual case may take longer to respond. Although unusual, sepsis and death have been reported.