45 Acral lick dermatitis
Canine acral lick dermatitis is a condition characterized by a firm, alopecic, frequently ulcerated plaque on a distal limb or limbs, caused by licking and usually complicated by a secondary bacterial infection. It used to be considered that the licking was purely the result of a psychogenic disorder, but it is now known that in many cases it is caused by a variety of pruritic or painful organic diseases, sometimes with a psychogenic component. This report describes a case of acral lick dermatitis in a Labrador.
A detailed history and full physical and dermatological examinations should help the clinician in determining whether the licking is the result of underlying organic disease, a psychogenic disorder or a combination of the two. The history should ascertain whether the skin disease is confined to the limb or whether there is, or ever has been, evidence of a more generalized skin problem. It is also important to establish the presence or absence of lameness in the affected limb, or previous injury.
Acral lick dermatitis usually develops on the limbs at the level of, or distal to, the mid radius or tibia. The anterior aspect of the carpus is commonly affected. Lesions may be single or multiple. The typical lesion is a raised, alopecic plaque with an eroded or ulcerated area at the centre of the lesion and a hyperpigmented margin. Some lesions may have draining sinus tracts and this should alert the clinician to the possibility of deep bacterial or fungal infection. There may be evidence of more generalized skin disease, such as otitis externa or pyoderma.
The examination should include manipulation of local joints and the neck (to assess for cervical pain), and palpation of underlying bone. If there is evidence of orthopaedic or generalized skin disease, these symptoms should be investigated and treated accordingly.
There are focal inflammatory, or neoplastic, disorders which may resemble acral lick dermatitis and that result in licking. In this case, there was evidence of aural erythema, which might have been evidence of a hypersensitivity disorder. The differential diagnoses included: