Hot Spot - AKA Moist Eczema

Hot Spots and moist eczema are common names for pyotraumatic dermatitis.  Pyotraumatic dermatitis is a rapidly developing surface bacterial skin infection secondary to self-induced trauma due to pain or pruritis.  Pruritis may be defined as the sensation that elicits the desire to scratch.  In animals prurities manfests as self-induced trauma due to licking, chewing, rubbing, hair removal and irritability, and may even involve personality changes.  The skin functions as an "external nervous system".  It contains free nerve endings responsible for continuously relaying sensory inputs, relating to touch, temperature, pain and pruritis to the brain or central nervous system.  Pruritis initiates a scratching response, however the mechanisms by which scratching alleviates itching are still unknown. 

The majority of pyotraumatic dermatitis cases are complications of flea bit hypersensitivity.  Other underlying causes may include allergic skin diseases due to food hypersensitivities or hypersensitivity to environmental factors (atopy), other ectoparasites (e.g. sarcoptic mange or Chevletiella mites commonly known as walking dandruff), anal sac problems, inflammations such as otitis externa (infection of the skin covering the outer ear canal that leads into the ear drum), foreign bodies in the coat, irritant substances which comes in contact with the animal's skin, dirty unkempt coats, phychoses including anxiety, boredom, separation and obsessive compulsive disorder, and painful musculoskeletal disorders.

It is usually a seasonal problem, being more common when the weather is hot and humid.  It commonly occurs in dogs, especially thick-coated, long-haired breeds, but it rarely occurs in cats.

Lesions are usually single but may also be mulitple.  Lesions are often painful, and they are often located in close proximity to the primary painful process.  Lesions most frequently occur on the trunk, tail base, outer thighs, neck or face.  Lesions are acutely pruritic (having a sudden onset) and the area of reddened (erythema), weeping and eroded skin with accompanied hair loss (alopecia) and well demarcated margins enlarges rapidly.

A diagnosis of pyotraumatic dermatitis is usually based on a history of sudden or acute onset, the physical appearance of the lesions, and some association with a primary cause.  A skin imprint on a glass slide when studied under a microscope will reveal inflammatory cells and mixed bacteria.

Treatment involves the identification and treatment of underlying cause.  Sedation or anaesthesia may be needed to thoroughly clip and clean the affected area with povidone-iodine or chlorhexidene.  Where clipping is not possible in show dogs, an antiseptic shampoo should be used on the unclipped affected areas.  The nature of additional treatments will depend on the severity of the lesion and the patient.  If the pruritis is mild, topical therapy is indicated and it involves the application of a cream or a solution containing an antibacterial agent and a corticosteroid 2 - 3 times a day for 5 to 14 days.  If the pruritis is severe, topical as well as systemic therapy is indicated.  Systemic therapy includes antibiotic and corticosteroid tablets or injections.  To prevent further self-induced trauma, the application of an Elizabethian collar may be indicated.

Therapy is effective if it is applied promptly and vigorously, and the prognosis is good if the underlying cause can be corrected or controlled.

Veterinary articles supplied by Dr S Strydom and published with kind permission of DIA Publishing - publishers of KUSA Dogs in Africa Magazine

Dr Sunelle Strydom qualified as a veterinarian in 2004 at the Faculty of Veterinary Science, University of Pretoria.  She has a passion for writing and the sharing of knowledge to promote animal health and welfare.  She has written several articles for KUSA Dogs in Africa as well as for Vra vir Faffa on the Landbouweekblad website at www.landbou.com