Acral lick granuloma (Acral lick Dermatitis, acral pruritic nodule)


What Is An Acral Lick Granuloma/Dermatitis?

Canine acral lick dermatitis is a spontaneously occurring disorder in which excessive licking of paws or flank can produce ulcers and infection that require medical treatment. A lick granuloma is a moist, fleshy, pink/red, sore patch of skin instigated by the trauma of constant licking by the dog at one site, usually on the upper part of the foreleg between the paw and the elbow. However, other locations can be observed too. Lick granulomas are an expression of an underlying prickly disease that tends to express itself in a focal point rather than in a generalised manner, and it requires proper diagnosis and treatment (Rapoport, et al., 1992).




Figure 1: Discolored coat in a light-haired dog as a result of constant licking besides the lick granuloma (acral lick dermatitis).



Figure 2: Acral Lick Dermatitis: a focal alopecic erosive lesion on the medial aspect of the distal leg is typical of this disease.




Figure 3: Canine acral lick dermatitis or lick dermatitis following the persistent licking of a focal area on a distal extremity presenting as a hyperpigmented alopecic well-circumscribed plaque with an ulcerated surface. In this case, the only inciting factor was a tick bite in this area four months earlier

Most lick granulomas happen at a spot that is easily accessed by the dog. Generally, the left foreleg is habitually picked as it is comfortable to reach when the dog is lying down. In some cases, the licking may be a manifestation of pain (e.g. arthritis in older dogs) that could have been triggered by some trauma in the area. It is common in large breeds of dogs.

The act of licking causes the discharge of endorphins (natural opiate hormones that are produced to ease pain and create calmness and joy. Endorphins are sometimes called "natural pain killers") in the dog's brain. Once the dog learns that licking brings about this pleasant feeling, the licking keeps going on producing a fleshy pink mass known as a granuloma at the site. The area will usually always be moist and may become particularly red and inflamed if infected. Many dogs lick themselves only when the owner is not present.


Causes Of Acral Lick Granuloma

Behavioural abnormality, is rarely the sole cause for this disorder, especially where the patient shows no other behavioural manifestations. Nevertheless, sooner or later, licking behaviour becomes a primary factor.

In many instances, the causal factor is a secondary problem, which includes:-

1. Allergies from food, airborne substances, or fleas.

2. Skin infections, including bacterial, e.g., pyoderma (Staphylococcus intermedius), leishmaniasis, sporotrichosis, furunculosis [ruptured hair follicles], fungal (ringworm), or yeasts.

3. Parasites (fleas, lice, mites, and some gastrointestinal parasites)

4. Skin diseases caused by immune system disorders.

5. Ruptured apocrine glands (Apocrine glands are found in the axillary, inguinal, perineal, and perianal regions and are associated with hair follicles).

6. Obsessive-compulsive disorder (Hewson, et al., 1998 )

7. Orthopaedic pins.

8. Other underlying causes include cancers, e.g., lymphoblastic lymphoma and mast cell tumour, or arthritis.

Therefore, presuming that all cases of acral lick dermatitis (lick granulomas) are behaviour-related may delay treatment of the real problem, and following a diagnostic protocol helps to rule out systemic, hormonal (e.g.reduced function of the thyroid gland) or metabolic diseases and these diseases tend to occur in older large breeds of dogs (Denerolle, et al., 2007).

These factors cause the skin to be itchy or painful, and, in some dogs, the initiating factor is minimal when compared to the psychological element. Lick granulomas develop mostly in anxious and highly-strung dogs. Still, it can also be seen in dogs that spend a long time alone or receive insufficient physical activity or mental stimulation, hence out of boredom. These issues, when addressed, resolve the issue (Shumaker, et al., 2008 ).


Diagnosing Acral Lick Granuloma

Lick granulomas have a typical appearance. However, it is possible for other conditions (particularly infections and tumours) to mimic this appearance, and it is crucial to be sure that the sore is not a tumour before treating it as anything else.

Proper identification of the underlying cause is crucial to the success of the therapy. If such a cause is not identified, lick granulomas may be extremely difficult to resolve. There are many underlying causes for lick granulomas, and these must be ruled out otherwise, the lick granuloma will keep recurring.


Generally, a combination of the following steps helps to diagnose acral lick granulomas.


1. Patient history.

  • When did licking start?

  • How often is licking noted (certain times of day or year, when the pet is alone or in the presence of others)?

  • Have there been any changes in the dog's environment or regular routine (e.g. moving, new baby or animal in household, loss of a family member)?

  • Is there any history of trauma, pain or surgical procedures?

2. Physical exam.

Clinical signs as listed above to get the best picture possible for an accurate diagnosis.


3. Skin cytology.

The area is squeezed to release exudate from the lesion, and then an impression smear is done. Since the sample is usually taken from regions that are too superficial, culture and sensitivity tests need to be done by obtaining purulent material through aspiration of acral lick dermatitis sample. On the other hand, a biopsy can be submitted for macerated tissue culture. Cultured organisms include Staphylococcus (60%), Pseudomonas (8%), and Enterobacter (8%).


3. Fine-needle aspiration.

This helps to rule out neoplastic diseases from nodular lesions.


4. Skin scrapings or trichograms.

· These are performed to rule out demodicosis.


5. Dermatophyte testing.

A fungal culture or polymerase chain reaction will identify dermatophyte infection as an underlying cause.


6. Dermato-histopathology and skin culture.

A skin biopsy for dermato-histopathology testing confirms a diagnosis and rules out some possible underlying causes. A skin culture then helps in antibiotic selection. A tissue sample is more informative than a surface swab as a deep bacterial infection is almost always present in these lesions.


7. Radiography.

Radiographs, with the support of an orthopaedic exam and history, help to identify a possible orthopaedic cause of licking if the patient has no signs of pruritus/allergies elsewhere and history suggests a painful underlying cause.


Treatment


1. Allergic Disease

Signs of allergic disease, e.g. flea allergy dermatitis, adverse food reaction, atopic dermatitis should be evaluated and depending on symptoms and history of the situation, assess the need for additional flea control, hypoallergenic diet trial, and allergy medication.


2. Bacterial infections

In acral lick dermatitis, 94% of patients have deep bacterial infections (Shumaker, et al., 2008 ), and antibiotic therapy is necessary to reduce infection in the tissue. Cultured organisms [Staphylococcus (60%), Pseudomonas (8%), and Enterobacter (8%)] are every so often multi-drug resistant and 25% are methicillin-resistant, so the empirical selection of antibiotics is not recommended but chosen from the results of culture and sensitivity.

In chronic cases, the bacterial infection is usually buried with fibrosis, and the infection tends to be "walled off", and an extensive course of antibiotics is necessary for a minimum of 4 weeks; 6–8 weeks or longer is not unusual. The patient is rechecked after four weeks of antibiotic therapy to determine the status of clinical signs. Antibiotics are administered until there is no evidence of exudation or moist dermatitis, hair regrowth is evident, and the resolution of acral lick dermatitis.


3. Use of Glucocorticoids

Glucocorticoids are usually administered concurrently with antibiotics to relieve inflammation and pruritus associated with foreign body reaction to free keratin (because of furunculosis and contents of ruptured apocrine glands). They are also used to treat pruritus associated with underlying allergic disease and are discontinued after the initial itch has been controlled. Antibiotics are then Continued to be administered after discontinuing the glucocorticoids as they may mask signs of remaining infection.

4. Surgical excision for extensive fibrosis (thickening of the skin)

Patients with a long-standing acral lick dermatitis may have extensive fibrosis surrounding areas of furunculosis. Chronic foreign body reaction and walled-off infection may also make resolution difficult. In these cases, surgical excision of the sore may be necessary. However, the surgical wound at the site may not heal well due to the dog licking at the stitches quickly the situation worse than before surgery. Delayed surgical wound healing can be prevented by using carbon dioxide laser ablation of the lesion, keeping the patient in Elizabethan collar, or changing the bandage daily until the surgical site has healed.


5. Use topical therapy

Topical therapy needs to be applied 2–3 times daily in conjunction with systemic antibacterial and anti-inflammatory treatment. The owner needs to observe the patient keenly to ensure that topical applications do not cause increased rubbing or licking of the lesion. The options include but not limited to Mupirocin (antibacterial) - can be used alone or followed by application of dimethyl sulfoxide (DMSO) to increase penetration. Several combinations of antibiotics and anti-inflammatories are also available, e.g. betamethasone and gentamicin. However, a culture and sensitivity test must be done so that the topical therapy used targets the isolated bacteria. Other creams containing local anaesthetics may be rubbed into the wound to reduce the desire to lick. Application of aversives like bitter apple spray (taste may discourage licking) may also limit licking. Alternatively, drugs that interfere with the transmission of neuropeptides (necessary for the transmission of pain and itch) can be used. Capsaicin, the active ingredient of chilli pepper, can be used topically on the margin of the granuloma.


6. Consider behaviour & environment

Antianxiety and behavior-Modifying drugs are used in conjunction with medical treatment if anxiety or behavioural abnormalities are potential or known. The medications used are Clomipramine (tricyclic antidepressant) at 1–2 mg/kg PO q12h and Fluoxetine (selective serotonin reuptake inhibitor) at 1 mg/kg PO q24h (Wynchank, et al., 1998)


7. Additional Considerations

Environmental factors (ie, excessive confinement, lack of exercise) need to be addressed.

Each therapy needs to be continued for at least four weeks after all signs of the sore have resolved. Even if the granuloma has wholly been resolved, there is still a risk of it recurring once treatment stops. One of the reasons dogs continue to lick the site is that licking the sore area releases natural endorphins (morphine-like substances) which make the dog feel good. In some instances, administration of an opioid drug, e.g. hydrocodone, can not only reduce irritation but may also fill the need for endorphins that the dog may be experiencing.


Prevention of lick granulomas

Lots of dogs have underlying allergies or hormonal diseases that should be addressed for complete resolution of an existing granuloma, as well as to prevent the relapse. Furthermore, tackling the potential psychological factors is essential and in some cases, simple changes in the environment (reducing stress or boredom), may suffice. Reduction in boredom is achieved by providing company for the dog, increasing exercise or training. In more difficult cases, mood-altering, antidepressant drugs such as Prozac or amitriptyline have been advocated, and some reports of success with acupuncture have also been reported.

Acral lick granulomas are very frustrating to treat. No simple cure and success will be achieved except by dedication and consistency in the approach of both the owner and the doctor.


References

Denerolle, P., White, S. D., Taylor, T. S., & Vandenabeele, S. I. (2007). Organic diseases mimicking acral lick dermatitis in six dogs. Journal of the American Animal Hospital Association (JAAHA), 43, 215-220.

Hewson, C. J., Luescher, U. A., Parent, J. M., Conlon, P. D., & Ball, R. O. (1998, December). Efficacy of clomipramine in the treatment of canine compulsive disorder. Journal of the American Veterinary Medical Association. ., 213(12), 1760-1766.

Rapoport, J. L., Ryland, D. H., & Kriete, M. (1992). Drug treatment of canine acral lick. An animal model of obsessive-compulsive disorder. Archives of general psychiatry, 49(7), 517–521. doi:10.1001/archpsyc.1992.01820070011002

Shumaker, A., Angus, J., Coyner, K., Loeffler, D., Rankin, S., & Lewis, T. (2008, September 29 ). Microbiological and histopathological features of canine acral lick dermatitis. Veterinary Dermatology, 19(5), 288-298. doi:https://doi.org/10.1111/j.1365-3164.2008.00693.x

Wynchank, D., & Berk, M. (1998). Fluoxetine treatment of acral lick dermatitis in dogs - a placebo-controlled randomized double-blind trial. Depress Anxiety, 8 (1), 21-23.

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