What are the main causes of hot spots on dogs?

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.

Canine hot spots, also known as pyotraumatic dermatitis or acute moist dermatitis, are red, inflamed skin lesions that appear quickly, ooze, and may contain pus. Hot spots can be found anywhere on a dog’s body, but the most common sites are the head, legs, and hips. These painful, itchy, smelly sores may be very obvious or may be hidden beneath matted fur.

What causes hot spots?

Hot spots are usually caused by self-trauma when a dog scratches an itch so vigorously that it creates an open wound. Many things can cause the initial itch in dogs including:

• Allergies including food allergies or inhalant allergies that cause itching.
• Reactions to insect bites from fleas, mites (Sarcoptes, Cheyletiella), or other small insects (e.g., caterpillars, bees, wasps, lice, gnats, or mosquitoes).
• Ear infections. Bacteria or yeast in the ear canal can be so irritating that the dog scratches at his ear, creating hot spots on the ear flap, behind the ear, or on the neck.
• Pyoderma. Primary skin infections also caused by bacteria or yeast may incite the dog to scratch an area so much that a secondary hot spot forms.
• Poor grooming. Dogs with unkempt hair coats bite at tangles, creating open wounds. Matted fur prevents air from reaching the skin and retains water after a dog swims or gets caught in the rain so the skin stays wet. This sets up a perfect environment for a hot spot.
• Boredom. Dogs, like people, develop bad habits. Instead of biting their fingernails, bored dogs lick areas that are easily accessible. When they lie down, the feet and forearms are right under their faces so hot spots often occur there.
• Orthopedic problems. Dogs with arthritis or back problems tend to lie down much of the time. Lying on one side creates abrasions over pressure points, like hips or hocks (ankles), where bony protrusions have little muscular padding, especially in elderly dogs with diminishing muscle mass. When the dog licks the abrasion, a hot spot erupts. Dogs also lick or chew at degenerating joints much like people rub a sore knee to relieve the pain, creating hot spots in the process.
• Anal gland inflammation. Infected or impacted anal glands are painful and annoying. Dogs lick the area around the rectum and can cause hot spots under or on top of the tail.

"Hot spots can dramatically increase in size in a very short period of time."

When a dog licks the sore spot, it irritates superficial nerve endings in the skin which stimulates more itching followed by more licking, biting, and scratching. This lick-itch-lick cycle is the basis for the self-trauma that causes hot spots. Hot spots can dramatically increase in size in a very short period of time. Pet owners may go to work after noticing a pinpoint area of redness and come home at the end of the day to find a raw lesion the size of a pancake.

How are hot spots treated?

The goal in treating a hot spot is to stop the trauma and prevent the development of a deep skin infection, so the first step in treating hot spots is to stop the self-mutilation. Some options to prevent your dog from doing this include:

• placing an Elizabethan collar (also known as an E-collar or cone) that stops the dog from chewing at the hot spot • covering the hot spot with a sock or bandage to act as a barrier

• topical or oral steroids and antihistamines to reduce the itching. Consult your veterinarian before using any medications intended for humans as they are often toxic to dogs.

It often takes a combination of all options to stop the trauma. In the meantime, the underlying cause of the hot spot must be addressed:

• If the hot spot formed as a result of impacted anal glands, they will need to be expressed. • If the cause is a flea allergy, a flea control protocol monthly (e.g., Frontline® Plus, Advantage® or Advantix®, Revolution®, Nexgard®, Simparica®, Bravecto®) to control the entire flea life cycle will be needed. • If arthritis is the culprit, your veterinarian may prescribe non-steroidal anti-inflammatory drugs (NSAIDs) such as meloxicam (Metacam®), carprofen (Rimadyl®, Vetprofen®), deracoxib (Deramaxx®), or other pain medications such as gabapentin (Neurontin®). • For inhalant or food allergies, your veterinarian can help you to begin avoidance or de-sensitization therapy and may recommend a hypoallergenic diet. • For ear infections, the underlying yeast or bacteria will be treated. • If boredom or behavioral issues are the reason your dog traumatizes himself, training and behavior modification, additional exercise and enrichment, and/or medications, such as antidepressants like fluoxetine (Reconcile®), clomipramine (Clomicalm®), or amitriptyline (Elavil®) may be the solution.

• If poor grooming is the cause, seek a professional that knows how to handle a pair of clippers.

"Clipping the hair away from the hot spot and the surrounding area is crucial to a successful treatment plan."

Clipping the hair away from the hot spot and the surrounding area is crucial to a successful treatment plan. The hot spot will heal more quickly if the hair is removed so that the lesion can dry properly. Grooming may be painful so your dog may need to be sedated beforehand. After clipping, the lesion should be disinfected with a chlorhexidine solution that kills bacteria. Topical antibiotics, desiccating sprays, and soothing reagents will be more effective when applied to a clipped, clean skin surface. Oral antibiotics and steroids/antihistamines may also be in order for serious hot spots.

How can hot spots be prevented?

Continued monitoring and treatment of the underlying cause should prevent future hot spots. Some dogs also benefit from seasonal grooming, as well as regular brushing and bathing.