The term “hot spot” is commonly used by pet owners to describe localized lesional areas of skin that may or may not be itchy to the dog. “Hot spots” are a common reason dogs are presented to the veterinarian. To a veterinary dermatologist, a “hot spot” is actually a condition so bothersome to the dog that we consider it an emergency. While we understand what pet owners are trying to convey by use of the term “hot spot,” pyotraumatic dermatitis or acute moist dermatitis is the proper term to characterize a true “hot spot.”
Pyotraumatic dermatitis is an acute moist dermatitis caused by self-induced trauma by the patient, as the dog bites or scratches at a part of the body to alleviate a pain or itch. Pyotraumatic dermatitis is different than pyotraumatic folliculitis. The skin surface is involved in pyotraumatic dermatitis, and the hair follicle is involved in pyotraumatic folliculitis.
Dogs that are predisposed to pyotraumatic dermatitis may have a heavy, dense hair coat (Golden and Labrador retrievers, Collies, German Shepherds, Saint Bernards, Newfoundlands, etc.). Warm, humid weather or frequent swimming may also predispose.
Causes of “Hot Spots”
Underlying causes of pyotraumatic dermatitis include ectoparasites (fleas), allergic diseases, anal sac problems, ear infections, foreign bodies in the skin/hair coat, reactions to topical substances, poorly kept coats, moist hair coats (from swimming or bathing), and arthritis. We also see many cases initiated by electric fence collars that get wet, permitting the overgrowth of bacteria. Any of these underlying conditions can trigger the itch-scratch cycle and lead to self-trauma.
Large painful lesions can be created by the dog in just a few hours. Lesions of pyotraumatic dermatitis are characterized by a well-defined alopecic (hair loss), flat, erythematous (red), moist, erosive dermatitis with a central surface coagulum and erythematous perimeter. Surrounding skin and hair are normal. One has to shave affected areas to reveal the extent of the lesion.
True pyotraumatic dermatitis will have bacteria colonizing the skin surface, but are not true skin infections. In pyotraumatic folliculitis and furunculosis, there is a skin infection. Here, the dog traumatizes skin in the area of a preexisting staphylococcal infection. One must clip and examine the lesion to differentiate.
Diagnosis of “Hot Spots”
Diagnosis of pyotraumatic dermatitis is made based upon the history of an acute onset, localized, painful, and associated with a primary trigger and some basic tests. Skin surface cytology to look for organisms and skin scrapings (to ensure there are no demodex mites) are done and results guide therapy choices.
Treatment of “Hot Spots”
The first step to treatment involves clipping and cleaning the area, usually with a chlorhexidine scrub. Other treatments will depend on the dog, pet owner, history, underlying cause, and extent. Drying agents such as 2% aluminum acetate may be used topically (Domeboro solution). One may also choose a 1% hydrocortisone with aluminum acetate solution (CortAstrin). Topicals should be applied two or three times a day until the lesion has healed. Because of the level of inflammation, most dogs benefit from an oral anti-inflammatories like the glucocorticoid prednisone for 7-14 days, if otherwise healthy. If papules or other follicular lesions are found, the term pyotraumatic folliculitis or furunculosis is used to name the lesion. This means the skin is infected and treatment will include systemic antibiotic therapy.
Staphylococcus pseudintermedius is the most common organism causing the infection. If the lesion is deep, then a bacterial culture may be recommended by the veterinarian. I recommend this test if initial therapy for S. pseudintermedius was not successful, if the lesion is deep, or if rod-shaped bacteria are seen upon examination of specimens collected for skin surface cytology.
See Your Veterinarian
We know the identification of a pyotraumatic dermatitis lesion on your dog is worrisome. Seek help from your veterinarian as soon as possible, so that they can initiate treatment and provide relief for your pet. To prevent “hot spots,” careful attention to grooming, bathing, ectoparasite control, ear cleaning, and control of underlying triggers such as food allergies and canine atopic dermatitis is important. The veterinarian can guide and advise you on the best plan for your pet.