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Summary
Also referred to as acute moist dermatitis or pyotraumatic dermatitis, hot spots are a common warm weather skin concern among dogs. These itchy, annoying, and sometimes impressively ugly areas of red, weepy, and hairless skin usually arise suddenly (hence the term "acute") and are often difficult to resolve.
A hot spot is caused by an initial traumatic incident, usually the result of conditions which prompt pets to scratch. Underlying causes include allergic skin disease, anal sacculitis, demodicosis, or other itchy skin conditions.
The upshot of this traumatic itchiness is usually the same: a puncture in the skin's protective barrier. Once this normal skin barrier is broken, microorganisms that naturally colonize the skin proliferate in the area and result in infection. These secondary infections are referred to as pyoderma and folliculitis.
The result of this bacterial colonization and skin damage is a lesion whose extreme itchiness is likely to lead to further scratching and self-trauma. Many of these hot spots will consequently grow into large patches of gooey infected skin.
Since heat and moisture encourage the growth of bacteria that cause hot spots, these lesions are more common during warm, humid times of the year. This is especially true for heavy-coated dogs whose dense undercoat traps both heat and moisture, creating ideal conditions for the skin's microorganisms to flourish.
Symptoms and Identification
Hot spots often appear suddenly (perhaps even overnight) as large sores that are itchy, painful, discolored and moist. They may appear reddish to greenish and shiny or weeping with ooze. They can occur anywhere in the body but tend to be located in areas most predisposed to allergic reactions (around the ears, neck, face, tail base and flanks).
Hot spots are usually diagnosed by visual examination of the area, but the following tests may be undertaken in the course of more comprehensive diagnosis of hot spots and their possible underlying causes:
Visual inspection for external parasites
Impression smear for cytological evaluation
Skin scraping to help identify mites, if present
Skin culture
Response to treatment for allergic skin disease
Specific allergy testing
Skin biopsy
Affected Breeds
While all breeds of dogs are susceptible, those who suffer allergic skin disease at higher rates are affected more frequently. These include dogs predisposed to allergic otitis externa, flea allergies and other forms of allergic skin disease.
Treatment
Hot spots are considered highly treatable, but frustrating to deal with. Because they're often intractable via topical medication alone (including sprays, powders and shampoos), injectable and/or oral medications are often required to resolve the condition.
During treatment, the infected area is clipped and cleaned. An initial injection of a short-acting corticosteroid is often given. This may preempt the need for longer-term corticosteroid therapy and antibiotics. If the area affected is vast, however, antibiotics are usually in order.
Additionally, shampooing and spraying with medicated products along with avoidance measures, such as Elizabethan collars, are considered fruitful in treating the condition and halt the itch/scratch cycle that usually perpetuates the problem.
Veterinary Cost
The cost of hot spot diagnosis and treatment depends to a large extent on the severity of the individual lesion and the frequency of the issue's recurrence.
For example, if hot spots are an annual or semi-annual occurrence independent of any other obvious manifestations of allergic skin disease, owners may elect to treat each episode symptomatically and not as ongoing evidence of an underlying allergic skin disease.
As such, the issue may be less expensive since the cost is limited to simple diagnosis and treatment (typically between $100 and $200). If, however, more comprehensive diagnostic tests are recommended, the expenses will often rise significantly. This is especially true of in-depth allergy testing, which may run up to $1,000 or $2,000 on average.
Prevention
Preventing hot spots isn't often easily accomplished except via all-inclusive treatment of the underlying skin disease.
As hot, humid weather conditions are known to exacerbate this condition, keeping pets indoors may prevent the onset of these lesions. So, too, can the early use of avoidance measures such as the Elizabethan collar.
References
Moriello KA. Treatment of dermatophytosis in dogs and cats: review of published studies.Veterinary Dermatology. 2004; 15.
Olivry T, DeBoer DJ, Favrot C, et al. Treatment of canine atopic dermatitis: 2010 clinical practice guidelines from the International Task Force on Canine Atopic Dermatitis. Veterinary Dermatology. 2010; 21: 233-248.
Scott DW, Miller WH Jr, Griffin CE. Canine demodicosis. Muller and Kirk's Small Animal Dermatology. Philadelphia, W.B. Saunders, 2001: 457-474.
Srivastava Mukesh, Ahuja Anil, Kachhawaha Subhash, Ankita. Management of Acute Moist Dermatitis in a Dog. Intas Polivet. 2013, 14:2.