Nail disorders are relatively rare in companion animals, particularly in comparison with nail disorders in man (1-6), which are numerous and related to various causes (7). Anatomy of the canine claw unit has been well described (1,8,9,10).
Clinical signs (1-4)
Onyxis is by definition the disease of the abnormal looking nail. It can be proximal, distal or it may involve all the nail. It may affect only one nail or be multiple depending on the cause. Perionyxis is the inflammation of the nail fold. Onychoschisis means fissuration (splitting) of the nail. Onychorrhexis is the breaking of a nail which has become brittle. Onychogryphosis is a deformation of the claw. It appears to be elongated and distorted. Onychomadesis is the sloughing process of nails. Onychoclasis is the fracture of the claw. Trachyonychia is a nail disorder in humans characterized by lustreless, longitudinally ridged and rough-surfaced nail plates. Pruritus is rarely observed in nail diseases. Pain is more common. However neither pruritus nor pain will be noticeable in many cases such as onychogryphosis.
Diagnostic approach
This shall be based on history, physical examination and complementary diagnostic aids, including biopsy by amputation or without onychectomy (11).
Consideration of particular diseases (1-4,9)
Traumatic onyxis is a very common disease in the dog. It usually affects only one nail, in particular the thumbnails (digit 1) on the hind legs. The nail is more or less distally broken and pain is usually observed. Diagnosis is clinically obvious. Therapy consists in promptly removing the distal part of the nail with forceps. A bandage is then applied for a few hours. If this is done a few days after the fracture, systemic antibiotics should be used for a week to prevent secondary bacterial infection.
Bacterial onyxis exists in the dog but is much rarer in the cat. In the latter, it is usually associated with an immunodeficient state (FeLV and/or FIV infection, diabetes mellitus etc...). In the dog, it may be idiopathic or secondary to an underlying disease (such as hypothyroidism, or even Cushing's disease). Perionyxis, onychoschisis, onychorrhexis and onychomadesis are usually seen on several nails, with pain as the primary complaint. Diagnosis is made by cytology-which reveals a bacterial pus (degenerated neutrophils, phagocytosis), bacteriology and the response to therapy. Treatment must be based on the removal of broken nails, topical antibacterial therapy and long term systemic antibiotic therapy (based on bacterial cultures and sensitivity testing, Staphylococcus sp. and Gram negative rods often being cultured). Months of careful therapy are needed, until the distal abnormal part of the nail has disappeared. In all cases, and particularly in chronically relapsing ones, an underlying disease should be suspected and, if found, treated. Bacterial pododermatitis, whatever the cause, often leads to bacterial onyxis. Good examples are interdigital pyodermas due to demodicosis and allergic skin diseases. Perionyxis is a prominent feature in such cases. Therapy appropriate to the causal pododermatitis will cure the nail problem if carried out for long enough.
Dermatophytic onyxis is a rare cause of onyxis and perionyxis in the dog, usually with one or a few digits being affected. In Aquitaine, Microsporum gypseum and Microsporum canis have been found to be the dermatophytes which most frequently cause fungal onyxis. Alopecia of the corresponding digit is often observed. Diagnosis is made by Wood's light examination which may reveal the fluorescence of the hair of the digit involved, direct examination and fungal culture of this hair, and histopathology of the nail itself. Skin biopsy and the removal of the third phalanx are unnecessary. PAS staining of the nail is mandatory and reveals the invasion of the nail keratin by the fungal hyphae. Long-term antifungal therapy (griseofulvine, ketoconazole, itraconazole) is necessary until the abnormal part of the nail disappears distally. This may take several months. Other cutaneous lesions should be topically treated simultaneously. Dermatophytic onyxis appears to be extremely rare in the cat. The author has never made such a diagnosis in a feline.
Malassezia perionyxis can be seen in atopic dogs, with a brownish staining of the claw, a greasy exudate in the claw folds and persistent pruritus (12). Malassezia pachydermatis and Candida albicans can be isolated from claws of Bull Terriers affected with lethal acrodermatitis (13).
Onychogryphosis is a classic symptom of canine leishmaniasis. In the enzootic area such a complaint justifies serology and/or a parasitological examination (skin and/or bone marrow cytology). Comprehensive therapy (Lomidine®, Glucantime®, amphotericin B, allopurinol) and a strict follow-up are mandatory.
Onychorrexis and onychomadesis can be seen in chronic cases of pododermatitis caused by ankylostomiasis. Diagnosis is made by cutaneous histopathology and coproscopy.
An inflammatory skin disease of the digits (pododermatitis) is observed clinically in canine atopic dermatitis and food allergy or intolerance. Onychogryphosis is frequent, often associated with perionyxis and redness of the hair on the digits. The nails may appear reddish in dogs whose nails are normally white but this may be due to secondary Malassezia infection. A diagnosis is obviously reached by evaluating all the symptoms observed in these diseases, by skin-testing, serology and elimination diets. Therapy includes allergen eviction, hyposensitization and symptomatic treatment (systemic glucocorticoids, antihistamines, essential fatty acids, topical antipruritic agents etc.).
Auto-immune (and immune-mediated) dermatoses usually affect several digits.
Discoid lupus erythematosus is a not so uncommon cause of onyxis in the dog (3,9,14). In fact, as the disease is symmetrical, as focal thickening and smudging of the basement membrane zone are not seen and as direct immunofluorescence testing is negative, Danny SCOTT named this disease «Symmetrical Lupoid Onychodystrophy» in 1995 (15). It is a real interface onychitis. Onychorrhexis and onychogryphosis are the main features of the disease. Other lesions may be seen in other areas of the body, but this is not always the case. Perionyxis is not always pronounced and skin biopsies of the nail bed area may be unrewarding. Amputation of the third phalanx is often the only way to reveal the typical hydropic and lichenoid interface dermatitis. Alternatively, a 8mm punch biopsy of the nail fold can be performed. This technique is applicable mainly to interface onychitis (it seems that in other conditions the resistance of tissues is higher). Immuno-suppressive doses of glucorticoids (prednisolone) may control the disease. Vitamin E and essential fatty acids (omega-3/omega-6 commercial compound) have been reported to be effective in some cases (3,15,16).
Nails and nail beds may be affected in pemphigus vulgaris (17). Onychogryphosis and onychomadesis can be observed. Severe perionyxis is also present, with erosions around the nail bed which are a source of pain. Diagnosis is made by histopathology either by skin biopsies around the claw or alternatively by amputation of the third phalanx. Biopsies of lesions in other body areas may be diagnostic. Only a guarded prognosis should be made. Immunosuppressive therapy should be carried out (glucocorticoids, azathioprine).
Onychogryphosis and perionyxis can be observed in canine pemphigus foliaceus, particularly in severe forms of the disease. A unique case of pemphigus foliaceus restricted to the claws has been diagnosed by E. Guaguère and J.P. Magnol (9). When pemphigus foliaceus is exclusively confined to the footpads onychorrhexis is often observed. The author has seen 2 cases of pemphigus erythematosus confined exclusively to the footpads, with onychorrhexis. Diagnosis can be made by histopathology. In the extensive forms of the disease (pemphigus foliaceus), biopsy of the skin lesions may be diagnostic. In the localized forms, biopsy of the footpads and/or an amputation of the third phalanx may be diagnostic. Immunosuppressive therapy is necessary.
In the cat, pemphigus foliaceus is a possible cause of severe perionyxis. A thick pus is discovered in the nail bed. Diagnosis is usually made by skin biopsy of the other skin lesions. Glucocorticoid immunosuppressive therapy is helpful.
Severe multiple onychomadesis and/or severe onychogryphosis with ulcerative perionyxis may be seen in the bullous pemphigoid group skin disease (a group of auto-immune disorders with subepidermal clefting as a common feature). They may even be the prominent features of this disease, making it a most painful one. Diagnosis is made by biopsy of the skin lesions, particularly of the digits, if there is ulceration around the nail bed. Alternatively, amputation of the third phalanx of an affected digit may be the only way to diagnose such a condition if only nail disease is present. In one case, the author had the luck to establish a diagnosis of bullous pemphigoid by removing nails from a dog with onychomadesis; a small amount of skin tissue still attached to the claw displayed the typical lesions of dermal-epidermal clefting. Therapy is not easy. Glucorticoid immunosuppression is not always helpful.
Systemic lupus erythematosus, cold agglutinin disease, drug eruption and vasculitis may affect the claws (3,4).
Trachyonychia has been seen in a dog with alopecia areata (18). A cat affected with pseudopeladehad onychomadesis (19).
In Man, Raynaud's disease is due to a spasm of digital arteries due to cold, which may be either secondary (e.g., to SLE) or idiopathic. It is a cyanotic/hyperhaemic and painful disease. Three female dogs (2 Boxers of 3 and 4 years of age and a 5 year-old mongrel) were suspected by the author to have a Raynaud-like disease (9). The patients were in severe pain from several digits which from time to time looked cyanotic. Onychogryphosis was prominent. Skin biopsies were performed in 2 dogs around the claws and showed non specific superficial dermatitis and a few Malassezia in the stratum corneum in one dog. Direct immunofluorescence testing was negative for IgG and C3. ANA test was negative in the 3 dogs. Long term therapy with isoxsuprine, a vasodilatator, at the dose of 1mg/kg/day, was very helpful.
Idiopathic onychomadesis has been described in dogs (11,20,21) although some of these cases could be undiagnosed cases of interface onychitis, particularly when biopsies were not done.
Keratinization diseases: the author has seen severe multiple onychogryphosis in cases of canine ichthyosis. However, generalized skin lesions were prominent and histopathology of the lesions confirmed the diagnosis (9). Many cases responded partially to retinoid therapy.
Some cases of zinc responsive dermatosis observed in Nordic dogs involve several digits. Two cases restricted to the digits, with a prominent perionyxis and above all onychorrhexis were observed by the author in Malamutes (of 10 and 12 months of age respectively) (9). Diagnosis was made by histopathology, with biopsies taken around the nail bed. There was a dramatic response to zinc sulfate supplementation (15 mg/kg BID) whereas zinc methionine had not been very helpful.
Several cases of idiopathic nosodigital hyperkeratosis in the older dog may be associated with mild multiple onychogryphosis.
Genodermatoses. Ichthyosis is a hereditary keratinization disorder. Onychogryphosis can be seen in canine dermatomyositis (Collies, Shetlands, Beaucerons) and epidermolysis bullosa (Beaucerons) (22). Glucorticoids, vitamin E and pentoxifylline are helpful. A similar hereditary condition could exist in the cat, with onychomadesis (23).
A case of congenital linear epidermal nevus ending in the paw of a hindleg was diagnosed by the author in a 3-year-old Pyrenean shepherd, with a prominent onychogryphosis on 2 digits (and a secondary demodectic pododermatitis as well). The nevus responded well to retinoid therapy (etretinate 1 mg/kg/day during 18 months followed by acitretin, at the same dosage, during 8 months).
Idiopathic onychogryphosis is observed in dogs. It usually affects one digit. Diagnosis is made by the elimination of other possible causes. Regular removal of the nail affected is advisable. The author has seen multiple inverted papillomas in a 7-year-old mixed French Spaniel associated with a severe onychogryphosis of only one digit. Papillomas can cause the development of cutaneous horns and potentially this claw alteration was linked to the skin disease.
Neoplasia of the nail fold is a common cause of onyxis and onychomadesis in the old dog. Squamous cell carcinoma (which is often misleading since it looks like a non-healing wound), melanoma, and mast cell tumour are relatively frequent. However, nailbed epithelial inclusion cyst, keratoacanthoma, inverted papilloma, and eccrine adenocarcinoma may also be observed (3,24). These tumours affect only one digit usually, and necessitate aggressive excision therapy. Melanoma and mast cell tumour may metastase, although squamous cell carcinoma has a better prognosis than usually believed if excision is carried out at an early stage. Swelling is often prominent and pain is acute. Diagnosis is made by histopathology of the removed tumour and radiographs of the digits often reveal bone lysis. Multiple squamous cell carcinomas are seen in black dogs, affecting several digits, with a slow growth rate and rare metastasis (3,25). Excision therapy is mandatory. Nail bed tumours are rarer in old cats. Those that do occur are squamous cell carcinoma, hemangiosarcomas, and metatasis of primary lung carcinomas (4,24).
Conclusion
Claw diseases in dogs and cats are often diagnostic and therapeutic challenges. A detailed case history, a thorough physical examination and appropriate complementary examinations are required to establish a diagnosis. The latter include cytology, bacteriology, mycology, histopathology (skin biopsy around the nail bed or even third phalanx amputation, sometimes very helpful) and immunological tests such as skin-testing and elimination diets. Therapy must be specific. In all cases appropriate follow-up is most important.
References
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