Ralf S. Mueller, DipACVD, FACVSc
Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University
Fort Collins, CO 80523, USA
Conférence présentée en 2003 lors des journées du Groupe de Travail Belge en Dermatologie Vétérinaire
Dogs and cats with claw diseases are presented infrequently in small animal practice. However, inflammation and/or infection of claws frequently are very painful due to the anatomical features of this structure (the dermis and noncornified epidermis are situated between the stratum corneum comprising the hard claw horn and the bony third phalanx and no subcutis is present). Thus, claw disease may be a cause of great distress to patient and owner alike. I will cover a diagnostic approach to claw disease and mention possible underlying diseases.
Diagnostic approach to claw disease
History. As with any dermatologic problem, a thorough history is crucial. It allows formulating and prioritizing differential diagnoses and choosing the appropriate diagnostic tests to rapidly achieve a diagnosis. Trauma such as a car accident may cause onychomadesis and secondary infections. An acute onset of disease is more common with autoimmune disease or trauma, while a slow progression is seen particularly with fungal infections or keratinization defects. Systemic signs such as lameness or polyuria/polydipsia may point to specific systemic diseases such as lupus erythematosus involving the claws and/or claw beds. If other animals or humans in the household are affected with skin disease, dermatophytosis may be higher on the list of differential diagnoses.
A thorough examination should be performed evaluating not only the claws and claw beds of all feet (including the dew claws, if present) but also the skin in general and particularly the mucous membranes, which may show lesions in patients with autoimmune diseases such as bullous pemphigoid or pemphigus vulgaris.
If single digits are affected only, trauma is more likely in a young dog. In an older dog with a single digit involved, neoplasia should be considered. In most cats with single affected digits, trauma is the cause of the problem. An underlying disease process of the bone of the third phalanx may also lead to claw disease affecting only one digit.
Systemic diseases such as autoimmune diseases or food adverse reactions commonly affect multiple digits and typically involve the dewclaws, which are less commonly affected with traumatic events.
Onychorrhexis (brittle claws) may be a result of chronic infection or a degenerative change frequently seen in older dogs, particularly Bullterriers. Nutritional deficiencies may also cause onychorrhexis.
Inflammation of the claw fold or paronychia may be associated with claw disease and is frequently caused by secondary infection with bacteria or yeast organisms. Pemphigus foliaceus may also cause paronychia, particularly in cats.
Cytology. Evaluation of claw or claw bed cytology for microorganisms and inflammatory or neoplastic cells is a useful, inexpensive and simple diagnostic tool. Many animals with claw disease will have concurrent paronychia and an impression smear may be obtained by pressing a slide onto the area adjacent to the claw. More useful may be obtaining material from the claw fold and/or claw surface with a swab or small paintbrush. This material is then applied to a glass slide and stained with a modified Wright’s stain such as DiffQuick or a Gram stain. Neutrophils with intracellular bacteria are diagnostic for a bacterial infection and antimicrobial treatment is indicated. The presence of bacteria alone may be due to bacterial infection or contamination and clinical judgment will determine the use of antimicrobial agents. Numerous yeast organisms indicate the need for antifungal therapy. However, both yeast and bacteria are rarely primary causes of claw disease and more typically secondary to other disease processes.
I don’t commonly use bacterial culture, empirical therapy will resolve most bacterial infections. However, if cytology reveals an unusual organism instead of the typically seen cocci or if empirical therapy with appropriate antibiotics at the appropriate dose fails to resolve the infection, cultures are of benefit.
Antimicrobial topical therapy (for example with chlorhexidine at 0.1%) may be beneficial, an alternative to daily shampoos or soaks is 2% mupirocin ointment applied twice daily to affected claws and claw beds. Systemic antibiotics are frequently indicated in patients with claw disease and secondary infection. Staphylococcus intermedius is the most common organism involved. Antibiotics used to treat bacterial infections may include erythromycin at 15 mg/kg q 8 h (gastrointestinal adverse effects are not uncommon), trimethoprim- sulfonamide combinations at 30 mg/kg q 12h (which may cause keratoconjunctivitis sicca or other drug reactions in some dogs and cats and causes excessive salivation in most cats at the time of administration due to the bitter taste of the drug), ormethoprim-sulfadimethoxin at 30 mg/kg q 24h after an initial loading dose of 55 mg/kg, lincomycin at 20 mg/kg q 12h, clavulanic acid/amoxycillin at 12.5 mg/kg q8h, cephalexin at 25 mg/kg q 12h, enrofloxacin at 5-10 mg/kg q 24h and others. Therapy is continued for 1-2 weeks beyond clinical and cytologic cure and may have to be continued for several months in severely affected patients. Diagnosis and treatment of an underlying disease is important to prevent recurrences of the infection. If appropriate therapy does not resolve the infection, a bacterial culture is indicated and the choice of antibiotic will be influenced by the culture and sensitivity results.
Fungal culture is indicated for all patients where fungal infection is suspected. Prior to culture, the claw may be cleaned with alcohol to reduce bacterial contamination. Scales of the claw fold or the proximal claws, part of avulsed claws and hair from the skin adjacent to the claw fold may be sampled. Onychomycoses are common in human dermatology, but fungal organisms rarely cause claw disease in small animals. However, if onychomycosis occurs, it often is refractory or recurrent. Antifungal therapy may include griseofulvin at 50 mg/kg q 12h, ketoconazole at 10 mg/kg q 12h, itraconazole at 10 mg/kg q 12-24h or terbinafine at 20-40 mg/kg q 24h. Prolonged therapy is needed and should extend at least 1-2 months beyond clinical and mycological cure. In animals with financial constraints, onychectomy may be considered. Recurrent disease may require daily low dose maintenance therapy in some patients.
Complete blood counts, serum biochemistry and urinalysis may be useful in dogs or cats with clinical clues for systemic disease such as hyperadrenocorticism or systemic lupus erythematosus, but have rarely been of benefit in patients with claw disease only.
Elimination diet. Exclusive claw disease due to food adverse reactions has been reported. An elimination diet for 8-12 weeks using a protein source and a carbohydrate source not previously fed will lead to normal claw regrowth and resolution of clinical signs in patients with food adverse reaction. Rechallenge with the old diet leads to recurrence typically within days. Sequential rechallenge with individual proteins may reveal the offending antigen. If a sequential rechallenge was performed and the offending antigen identified, avoidance of that particular antigen will result in long-lasting clinical remission without the need for further treatment. Some owners may be reluctant to go through a sequential rechallenge and want to keep the dog on the elimination diet. If a home-cooked diet has been used, it is important to evaluate if the food is balanced and complete. Input from a nutritionist may be useful. Long term maintenance on a commercial diet restricted to unusual proteins is an alternative.
Biopsy of the claw, claw matrix and claw fold is essential for the diagnosis of neoplasia or immune-mediated disease such as pemphigus. It may also identify fungal or bacterial organisms. However, interface onychia with vacuolization of keratinocytes, pigmentary incontinence and a lichenoid, mononuclear infiltrate has been observed in dogs with confirmed bacterial infections or food adverse reactions and may be a reaction pattern of the canine claw rather than a feature diagnostic of immune-mediated disease. An onychobiopsy technique without the need for onychectomy has recently been described. An 8 mm biopsy punch is used to obtain a sample containing the lateral aspect of the claw and bony third phalanx as well as part of the lateral claw matrix, claw fold and adjacent skin. The technique is very useful, but some practice may be required before diagnostic samples are obtained. It can only be used in diseased and thus softened claws. The alternative is removal and submission of the third phalanx of an affected digit. This is particularly recommended for dogs with possible neoplastic disease, see below.
Radiographs may be useful for the evaluation of osteomyelitis in dogs with severe swelling and pain possibly necessitating surgical removal of that particular digit. If cytology or radiographs indicate possible neoplastic disease, immediate surgical removal of affected digits is the treatment of choice. Even though a variety of tumors such as melanoma, mast cell tumors, keratoacanthoma, inverted papilloma, lymphosarcoma, fibrosarcoma, osteosarcoma and others have been reported to affect the canine claw and claw bed, squamous cell carcinoma is the most common neoplasia of the distal digit. Large black dogs are predisposed for the latter. This tumor frequently invades P3. Lymph node aspirates or biopsies and radiographs are recommended to evaluate the extent of invasion and the possibility of metastases, which may dramatically alter the prognosis. If the local lymph nodes show evidence of neoplastic cells, excision of the affected lymph node or limb amputation is recommended.