Diseases restricted to the nail and/or nail fold are occasionally encountered in clinical practice. When disease involves only one or two nails, the most likely etiologies include trauma, bacterial or fungal infections, and neoplasia. When multiple nails are involved on all four feet, autoimmune or immune-mediated, genetic, endocrine, nutritional or immunosuppressive diseases should be considered.

This is a rare cause of nail disease. Trichophyton mentagrophytes is the most commonly isolated dermatophyte. Samples for fungal culture should be taken from the most proximal part of the nail plate, and multiple samples should be obtained. Nails can be washed with alcohol prior to placement on the culture media to reduce contaminants.

Bacterial infections of the nail are usually secondary to underlying local or systemic disease. Trauma (fracture, nails clipped very short) affecting only one or a few claws is most common. Bacterial cultures should be taken from the most proximal portion of freshly avulsed nails or nail fragments. Only the proximal portion should be placed in sterile transport media for submission to the laboratory; and alcohol should not be used to wash these samples. With chronic or severe cases, radiographs should be taken to evaluate for the presence of osteomyelitis.

When this involves multiple nails, a thorough clinical and laboratory work-up should be performed, including: CBC, chemistry profile; urinalysis; cytology, fungal and bacterial culture of affected nails; ANA, complete thyroid profile, radiographs, and a third phalanx biopsy. In the dog, pemphigus vulgarus, pemphigus foliaceus, bullous phemphigoid, systemic lupus erythematosus, lupus-like syndrome, cold agglutinin disease, drug eruption, and vasculitis have all been reported to cause symmetric onychomadesis and onychodystrophy (abnormal nail formation).

Metabolic epidermal necrosis (hepatocutaneous syndrome) may also cause nail loss, but other skin changes are usually present and affected patients usually have concurrent liver disease. One of the most common causes of generalized onychomadesis in the dog has been referred to as an idiopathic lupus-like or "lupoid" syndrome. While it has been recognized in many breeds, Rottweilers and German shepherd dogs are predisposed. The age of onset is variable, but tends to occur in young adult dogs (1-6 years of age). The onset may be acute and wide-spread or chronic, in which case only one or two nails are affected at a time. Paronychia (inflammation of nail fold) is usually not present, although affected nails may be painful and result in lameness. Left untreated, the tendency is to have partial regrowth of abnormal, friable nails that continue to be sloughed off. There is no apparent systemic involvement.

The diagnosis is based on ruling out other causes of nail disease and histologic evaluation of a third phalanx biopsy. The nail, third phalanx, and a small amount of the nail fold, excluding the pad, are harvested in a standard "declaw" fashion. The dewclaw (if involved) may be the site most readily harvested. Following removal of the claw, the site should be sutured perpendicular to the long axis of the toe to minimize post-operative pain. The sample should be placed in formalin and submitted to a veterinary histopathologist.

Histologically, there is usually widespread hydropic degeneration of the basal cell layer of the epidermis, mononuclear interface dermatitis, and marked pigmentary incontinence.

Treatment should include removal of loosened nail plates. Systemic antibiotic therapy is recommended for secondary bacterial infection. In a recent prospective study of 24 dogs exhibiting only claw disease, four patients showed complete or near complete remission when an elimination diet was instituted. In two of these patients, adverse food reaction was conclusively identified as the cause for the claw disease, suggesting that interface onychitis may not always be due to immune-mediated disease. Other recommended therapies have included prednisone at 2-4 mg/kg/day for 2-4 week, then half this dose for 2-4 weeks, then gradual reduction to the lowest every-other-day dose for maintenance. After several months of successful therapy, one should attempt to discontinue the medication. An alternative therapy involves the combined use of tetracycline and niacinamide as described for discoid lupus erythematosus. Fatty acid therapy at routine dosages also may be of benefit in some cases.

Squamous cell carcinoma, melanoma, mast cell tumor, kertoacanthoma, inverted papilloma, lymphosarcoma, eccrine adenocarcinoma, hemangiopericytoma, and various other sarcomas have all been reported to involve the distal digit/nail in the dog. Of these, squamous cell carcinoma is the most common. Large breed dogs with black coats, particularly Labrador retrievers, and standard poodles, are predisposed. Multiple digits may be involved over a course of 2-4 years. In the dog, they appear to be slow growing and metastasis is rare. However, treatment requires amputation of the involved digit. Melanomas of the canine digit are highly malignant.

References: Savary, KCM, et al, J Vet Int Med 14: 184-189, 2000. Rosychuk, RAW, Current Vet Therapy XII, Saunders, Phila, 1995, pp 641-647; Boord, MJ, et al, JAAHA 33: 131-138, 1997; Bergvall, K, Vet Dermatol 9: 263-268, 1998; Mueller, RS, Friend, S, et al, Vet Dermatol 11: 133-141, 2000.