1. hypertrophy of the horny layer (stratum corneum) of the skin, or any disease characterized by it; the hyperkeratoses may have distinctive formats, e.g. annular (ring formations), basket-weave, compact, laminated.
2. hypertrophy of the cornea.
- bovine h. — chlorinated naphthalene poisoning.
- digital h. — increased thickness of the keratinized epidermis of footpads in dogs and rarely cats. May be in response to trauma or associated with distemper (hardpad disease), or pemphigus foliaceus.
- epidermolytic h. — a form of ichthyosis in humans which is inherited as an autosomal dominant trait; there is severe degeneration of the granular layer of the epidermis.
- juvenile h. — a crusting dermatosis over bony prominences, face and chin of young dogs. See zinc-responsive dermatosis.
- nasal h. — an abnormal thickening, sometimes with fissures, of the planum nasale of dogs. May occur in association with digital hyperkeratosis (see above) as a feature of distemper (hardpad disease). Also seen in pemphigus foliaceus and discoid lupus erythematosus.
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| Nasal hyperkeratosis. By permission from Kummel BA, Color Atlas of Small Animal Dermatology, Mosby, 1989 |
- nasodigital h. — see nasal hyperkeratosis, digital hyperkeratosis (above).
- orthokeratotic h. — hyperkeratosis with non-nucleated cells present.
- parakeratotic h. — hyperkeratosis with nucleated cells present; called also parakeratosis.