Nail diseases (Proceedings)

Concurrent claw problems are not unusual in many skin diseases, but rare as the only dermatological problem. The most common disease affecting single claws are: trauma, bacterial or fungal infections; the most common condition affecting multiple claws would be onychodystrophy. The claw is important for the pet for grasping and holding, moving and used as a defense tool. For this reason it is important that the claws are regularly trimmed and healthy. Diseased claws will predispose to trauma, abnormal locomotion, pain, lameness, and pododermatitis. Various medical terms are used to describe the claw lesion such as: Paronychia (inflammation or infection of the claw fold), Onychodystrophy (abnormal claw formation), Onychogryphosis (hypertrophy and abnormal curvature of claw), Onychomadesis (sloughing of claws), Onychomalacia (softening of claw), Onychomycosis (fungal infection), and Onychoschizia (splitting of claw).

If a patient is presented with a claw disease a detailed history (e.g. vaccine can induce vasculopathy; started with one claw and is spreading typical for symmetric lupoid onychodystrophy) should be obtained and a thorough inspection of the affected claw should be performed. Cytology is very important and simple test to identify bacteria and yeast, which are very often a cause of secondary infection in abnormal claws. Bacterial and fungal culture is required if initial antimicrobial therapy did not cure the infections. Biopsies are usually required if multiple claws are affected and a systemic and immune-mediated diseases or neoplasia are suspected.

Trauma

Trauma is the most common cause for claw diseases in dogs and sometime in cats. Typically one or few claws are affected. In rare cases claws on all four feet are affected, which can occur due to excessive running on asphalt, concrete and gravel, or the use of infected nail clippers. Untreated claw trauma will often result in secondary bacterial infections.

The distal part of the affected nail should be removed and the foot bandaged if necessary. In older lesions with suspected infection, foot soaks with disinfectants, and oral antibiotics in more severe cases is recommended.

Bacterial claw diseases

Bacterial claw infections are common and are considered a secondary problem. The most common underlying cause is trauma. However, systemic diseases such as hypothyroidism, Hyperadrenocorticism, diabetes mellitus, hypersensitivities, immune-mediated diseases and onychodystrophy may cause claw infections. Chronic severe infections of the nail bed can result in permanent defective claw growth. Swelling of the nail bed area, pain and pus formation is typical. Cytology is the preferred diagnostic method. If the infections does not respond to initial antibiotic therapy a bacterial culture & sensitivity may be necessary.

To treat infected claws it is best to remove as much of the affected claw as possible. Topical antibiotics or in more severe cases oral antibiotics should be given until the lesion is healed and enough until normal claw is covering the previously affected area.

Fungal claw diseases

Fungal infections are rare and organisms which have been reported to claw and often the nail bed diseases are: Malassezia, dermatophytes (especially Trichophyton), followed by blastomycosis, cryptococcosis, sporotrichosis. Dogs with Malassezia infections show brown-red discoloration of the claw with brown-colored waxy exudate on the proximal aspects of the claws. This condition is very often seen in dogs with allergies. Diagnostic tests, which will help to identify the organisms, are: cytology, Wood's lamp, fungal culture, and biopsy.

Most of these fungal infections (except Malassezia) require aggressive systemic antifungal therapy. Itraconazole and terbinafine have shown to accumulate in keratin, horn, and hairs.

Parasitic diseases

Parasites such as Demodex do not affect directly the claws, but will result in secondary changes due to persistent inflammation and secondary infections if not treated appropriately. Demodex mites are often difficult to find on skin scrapes from pedal skin, due to their deep follicular localization in those areas. Sometimes skin biopsies are necessary to confirm a demodicosis on the feet. Other parasites which have been reported to cause onychogryphosis are Leishmania and hookworms, which may require specific laboratory test to confirm the disease.

Symmetrical lupoid onychodystrophy

Based on the clinical presentation, inflammatory pattern and response to therapy symmetric lupoid onychodystrophy should be considered to be an immune-mediated disease or vasculopathy. This disease can occur in different breeds (personally seen in Greyhound, Schnauzer, Labrador retriever), but German Shepherds are considered predisposed for this disease. The problem usually starts with one claw, but within a couple of weeks other claws become affected. The animals appear otherwise healthy, but once the claws start to slough off they become painful, show lameness, and secondary infections. The claw horn continues to grow, but the horn quality is poor. The claw appears short, discolored, deformed, soft, and crumbly and tends not to attach well to the underlying nail bed. Histopathology (hydropic and lichenoid interface dermatitis) is usually required to confirm the diagnosis. Because the histological lesions are located very deep at the claw base, amputation of the 3rd phalanx may be necessary to be able to diagnose the disease.

Treatment of this disease requires immunosuppressive therapy with steroids and high doses of omega-3 and omega-6 fatty acids (e.g. Derm Caps or Omegaderm) with Vit E, or tetracycline with niacinamide. Improvement and claw regrowth should be noticed within 3-4 months.

Auto-immune diseases

Very rarely auto-immune diseases such as Pemphigus vulgaris, foliaceus or erythematosus may affect claws besides other skin areas. A biopsy of the nail bed is usually required to diagnose the disease.

As with auto-immune diseases in general, immune-suppressive therapy is required to manage this disease.

Neoplasia

Among the most common neoplasia involving the claws, squamous cell carcinoma, melanoma and mast cell tumors should be considered. Other differentials such as inclusion cysts, keratocanthoma, and inverted papilloma should be ruled out. In cats nail bed tumors are rare, but metastasis of primary lung carcinoma, hemangiosarcoma and squamous cell carcinoma have been reported. Tumors usually form solitary lesions. Melanoma and mast cell tumors may be aggressive and tend to metastase. All neoplasia should be diagnosed by histopathology and aggressive excision or amputation of the affected digit is usually curative.

Miscellaneous rare claw diseases

Idiopathic onychodystrophy affect multiple claws in older dogs. This condition appears to be predisposed in Siberian husky, Dachshund, Rhodesian ridgeback, Rottweiler and Cocker spaniel. Biotic and gelatin may help to improve the horn quality of the claws.

Idiopathic onychomadesis has been reported in German shepherd, Whippet, and English Springer spaniel. Secondary claw infections are not uncommon. Anecdotal reports suggest the use of pentoxifylline.

Anecdotal reports of diseases such as epidermolysis bullosa, dermatomyositis, drug eruption, ergotism, thallotoxicosis, linear epidermal nevi, nutritional deficiencies, disseminated intravascular coagulation, and necrolytic migratory erythema do exist.