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Here's my synopsis of what is likely to be the problem:
Acral lick dermatitis is first noted as excessive, compulsive licking at a focal area on a limb, resulting in a firm, proliferative, ulcerative, alopecic lesion. Causes of the licking are multifactorial and although environmental stress (e.g., boredom, confinement, loneliness, separation anxiety) may be a contributor, other factors are usually more important - hypersensitivity (atopy - allergies to environmental allergens such as pollens, molds, dust, dust mites, etc.; food), fleas, trauma (cut, bruise), foreign body reaction, infection (bacterial, fungal), demodicosis (Demodex mange mite), hypothyroidism, neuropathy, osteopathy, arthritis). The dermatitis is common in dogs with the highest incidence in middle-aged to older, large-breed dogs, especially Doberman pinschers, Great Danes, Golden retrievers, Labrador retrievers, German shepherds, and Boxers.
The lesion usually begins as a small area of dermatitis that slowly enlarges because of persistent licking. The affected area becomes alopecic, firm, raised, thickened, and plaque-like to nodular and it may be eroded or ulcerated. With chronicity, extensive fibrosis (scarring), hyperpigmentation, and secondary bacterial infection are common. Lesions are usually single but may be multiple and they most often are found on the dorsal aspect of the carpus ("wrist"), metacarpus, tarsus, or metatarsus.
The underlying causes should be identified and corrected (see above) with the help of his vet. One should treat for secondary bacterial infection with long-term systemic antibiotics (minimum 6-8 weeks and as long as 4-6 months in some dogs). Antibiotic therapy should be continued at least 3-4 weeks beyond regression of the lesion. The antibiotic should be selected according to bacterial culture and sensitivity results. Anecdotal reports suggest good efficacy with combined antibiotic, amitriptyline (2 mg/kg every 12 hours), and hydrocodone (0.25 mg/kg every 8-12 hours) administered until lesions resolve. Then one drug should be discontinued every 2 weeks until it can be determined which drug (if any) may be required for maintenance therapy. Topical application of analgesic, steroidal, or bad tasting medications every 8-12 hours may help stop the licking but response is unpredictable and often disappointing. When no underlying cause can be found, treatment with behavior-modifying drugs may be beneficial in some dogs - anxiolytics, tricyclic antidepressants, endorphin blocker, and endorphin substitutes are all available through his vet. Trial treatment periods of up to 5 weeks should be used until the most effective drug is identified. Lifelong treatment is often necessary.
Alternative medical treatments such as cold laser therapy or acupuncture have been beneficial in some patients. Mechanical barriers such as wire muzzles and side braces may be helpful. Surgical excision or laser ablation isn't recommended because postoperative complications, especially wound dehiscence, are common. Laser ablation may help sterilize the lesion and deaden nerve endings; however, response is highly variable. The prognosis is variable. Chronic lesions that are unresponsive or extensively fibrotic and those for which no underlying cause can be found have a poor prognosis for resolution. Although the disease is rarely life-threatening, its course may be intractable.
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