Symmetric lupoid onychodystrophy
Immune-mediated disease of the claw-forming tissue that makes the claws slough one after another on all four feet. The claws that regrow are short, brittle and misshapen.
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What it is
Symmetric lupoid onychodystrophy (also called symmetric lupoid onychitis) is the most common cause of disease affecting the claws of several digits at once in the dog. An immune-mediated inflammation attacks the tissue that produces the claw, at the junction between the dermis and the epidermis of the claw base. The claws separate from the underlying dermis and fall off (onychomadesis), and the new claws grow abnormal. The trigger is unknown; a hereditary predisposition is suspected in some breeds.
Who it affects
Young adult and middle-aged dogs, usually between about 3 and 8 years of age. Predisposed breeds include the German shepherd, Gordon setter, English setter, Rottweiler and bearded collie, but any breed can be affected.
Anatomy involved
The claw (unguicula) is a horny capsule produced by the epidermis that covers the ungual process of the distal phalanx. The living, vascular dermis of the claw (the "quick") is attached directly to the bone, and the claw is formed at its base, under the ungual crest. Because the claw-producing tissue cannot be separated from the third phalanx, a biopsy that includes it requires amputation of the distal phalanx, usually of a dewclaw or of an affected digit.
Clinical signs
Sudden loss of one or two claws, followed within weeks to months by loss of claws on all four feet. The exposed dermis is painful and may bleed; dogs lick their paws and may be lame. Secondary bacterial paronychia is common. The regrowing claws are short, dry, soft or brittle, misshapen and discoloured, and may slough again. The rest of the skin is normal.
Diagnosis
- Typical history and symmetrical involvement of multiple claws.
- Exclusion of other causes of claw disease: bacterial or fungal (dermatophyte) infection, trauma, neoplasia, other autoimmune diseases such as pemphigus or lupus.
- Histopathology of an amputated third phalanx with its claw shows a lichenoid interface onychitis and confirms the diagnosis.
Treatment
Loose claws are removed under sedation and secondary infections treated. Long-term therapy combines omega-3 fatty acids with immunomodulating drugs such as doxycycline or tetracycline with niacinamide, pentoxifylline, ciclosporin or, in refractory cases, glucocorticoids. Because claws grow slowly, the response is judged over at least 3 to 4 months. Many dogs need lifelong treatment, but most regain functional, if imperfect, claws.
References
- Miller WH, Griffin CE, Campbell KL. Muller and Kirk's Small Animal Dermatology, 7th ed. Elsevier (2013)
- Hnilica KA, Patterson AP. Small Animal Dermatology: A Color Atlas and Therapeutic Guide, 4th ed. Elsevier (2017)