Camelidae and Cervidae Idiopathic Hyperkeratosis – NAVLE Study Guide

Overview and Clinical Importance

Idiopathic hyperkeratosis encompasses a group of poorly understood dermatologic conditions affecting New World camelids (llamas, alpacas) and cervids (deer, elk) characterized by excessive keratinization of the epidermis. In camelids, these conditions include zinc-responsive dermatosis, idiopathic necrolytic neutrophilic hyperkeratosis (INNH or "munge"), and congenital ichthyosis. In cervids, the primary hyperkeratotic condition is associated with papillomavirus-induced fibropapillomas. Understanding these conditions is essential for NAVLE preparation as camelid medicine questions appear regularly on board examinations.

Camelidae Hyperkeratotic Skin Conditions

Hyperkeratotic skin conditions in New World camelids (llamas and alpacas) are among the most challenging dermatologic problems encountered in practice. These conditions share clinical features of alopecia, scaling, crusting, and thickened skin, but differ in etiology, distribution, and response to treatment. Unlike other ruminants, camelids demonstrate unique susceptibility to zinc deficiency and distinctive cutaneous reaction patterns.

Zinc-Responsive Dermatosis (Idiopathic Hyperkeratosis)

Etiology and Pathophysiology

Zinc-responsive dermatosis in camelids remains incompletely understood. The condition may represent a true zinc deficiency or a keratinization disorder responsive to supraphysiologic zinc doses. Unlike other ruminants, llamas and alpacas appear uniquely susceptible to this condition. Factors that may contribute include dietary calcium excess (which interferes with zinc absorption), phytate-rich diets, increased zinc demands during growth or lactation, and possible genetic predisposition in certain fiber colors.

Clinical Signs and Distribution

The classic presentation is nonpruritic papules with tightly adherent crusts that progress to plaques and then to large areas of skin thickening. Lesions appear predominantly in lightly-fleeced or hairless areas: perineum, ventral abdomen, inguinal region, medial thighs, axilla, and medial forearms. The face may also be involved. Clinical signs characteristically wax and wane over time. Most commonly affects young animals (1-2 years of age) and females, though males can be affected.

Clinical Findings Summary

Diagnosis

Skin biopsy is the cornerstone of diagnosis. Histopathology reveals epidermal and follicular orthokeratotic hyperkeratosis with mild to moderate perivascular dermatitis containing lymphocytes, macrophages, plasma cells, and occasional eosinophils. Importantly, camelids show orthokeratotic rather than parakeratotic hyperkeratosis (unlike dogs, sheep, goats, cattle, and swine with zinc deficiency).

Serum zinc testing should be performed but has significant limitations. Normal serum zinc does NOT rule out zinc-responsive dermatosis. Blood samples must be collected into plastic tubes without rubber stoppers (rubber may contain zinc causing false elevations) using a plastic syringe. Hemolysis releases zinc from erythrocytes and must be avoided. Reference ranges: plasma zinc concentrations of 3-6 μmol/L have been observed in apparently healthy alpacas; concentrations less than 3 μmol/L may be associated with zinc-responsive lesions.

Treatment

Treatment involves oral zinc supplementation. Recommended protocols include zinc sulfate (1 g/day) or zinc methionine (2-4 g/day). Clinical improvement is typically seen within 30-90 days, though complete resolution may take up to 12 months. Concurrently, minimize calcium supplementation and discontinue alfalfa hay (high calcium content interferes with zinc absorption). Some animals require lifelong supplementation.

Idiopathic Necrolytic Neutrophilic Hyperkeratosis (Munge)

Etiology and Pathophysiology

Munge (also called INNH or idiopathic nasal/perioral hyperkeratotic dermatosis) is a poorly understood hyperkeratotic disorder representing a cutaneous reaction pattern rather than a single disease entity. It is believed to result from multiple triggering factors including bacterial folliculitis, dermatophilosis, dermatophytosis, contagious viral pustular dermatitis, chorioptic mange, fly bites, viral papillomas/fibropapillomas, contact dermatitis, and possibly zinc-responsive dermatosis. The term "munge" is colloquial and refers specifically to the nasal and perioral distribution of lesions.

Clinical Signs and Distribution

Two forms of munge are recognized. Focal INNH affects the perinasal and perioral regions with potential extension to periocular and periaural areas. In severe cases, thick crusts may obstruct the nostrils. Diffuse INNH is typically seen in llamas 1-2 years of age with more widespread distribution. Lesions are characterized by variable degrees of heavy, adherent, hyperkeratotic crusts. The inflammatory component may wax and wane over time.

Diagnosis

There is no definitive diagnostic test for munge. Diagnosis is based on clinical appearance and exclusion of other causes. Histopathology reveals parakeratotic and orthokeratotic hyperkeratosis with a seropurulent, palisading crust associated with epidermal hyperplasia and degenerate neutrophils. Skin scrapings, fungal culture, and bacterial culture should be performed to identify treatable underlying causes. Differential diagnoses include viral contagious pustular dermatitis, dermatophilosis, dermatophytosis, bacterial dermatitis, immune-mediated disease, and sarcoptic mange.

Treatment

Treatment is directed at identifying and treating underlying causes. Options include topical and/or systemic antibiotics for secondary bacterial infections, scab removal with antiseptic scrubs (dilute iodine or chlorhexidine), topical and/or systemic glucocorticoids (avoid in pregnant females as steroids may cause abortion in camelids), and oral zinc supplementation. Some cases regress spontaneously. A commonly used topical preparation called "Witches' Brew" contains gentamicin, ivermectin, dimethyl sulfoxide, and mineral oil. Animals with juvenile llama immune deficiency syndrome may not respond to any therapy.

Congenital Ichthyosis

Ichthyosis is a congenital disorder characterized by focal or diffuse hyperkeratosis and scaling caused by defects in terminal keratinocyte differentiation and desquamation. Unlike zinc-responsive dermatosis, lesions are present at birth or shortly thereafter. Histopathology shows prominent laminated orthokeratotic hyperkeratosis of the epidermis and hair follicle infundibula with minimal epidermal hyperplasia and absence of inflammation (which helps distinguish it from zinc-responsive dermatosis). Treatment is generally not attempted; oral retinoids (vitamin A derivatives) have shown promise in human and canine cases and may be considered.

Differential Diagnosis of Camelid Hyperkeratotic Disorders

Cervidae Hyperkeratotic Skin Conditions

In cervids (deer, elk, moose), the primary hyperkeratotic condition is cutaneous fibroma (deer warts) caused by species-specific papillomaviruses. While technically neoplastic rather than purely hyperkeratotic, these lesions demonstrate significant epidermal hyperkeratosis and acanthosis and are important differential diagnoses when evaluating skin conditions in cervids.

Papillomavirus-Associated Cutaneous Fibromas

Etiology

Cutaneous fibromas in deer are caused by species-specific papillomaviruses belonging to the Delta genus of Papillomaviridae. The virus induces fibropapillomas (skin tumors with marked connective tissue component where fibroblasts are the primary target cells). Transmission occurs through skin contact, sharing rubbing posts and bedding sites, or possibly via biting insects. White-tailed deer are most commonly affected, though papillomaviruses have been identified in elk, reindeer, roe deer, and red deer.

Clinical Signs

Lesions appear as firm, hairless, gray or black growths that can be smooth or rough (warty) in texture. Size ranges from less than 1 cm to several inches in diameter, and growths may occur singly or in clusters. Most commonly found on the head, neck, shoulders, and forelegs. Most infected deer have 5 or fewer tumors, though more than 200 have been reported. Histopathology shows hyperkeratosis and acanthosis of the epidermis with proliferation of fibroblasts and connective tissue.

Clinical Significance

Fibromas typically do not cause significant harm to the deer and usually regress spontaneously as the immune system clears the infection. They may become problematic only when located where they interfere with sight, breathing, eating, or movement. The virus is species-specific and does not infect humans, domestic animals, or other wildlife. Carcasses can be processed normally unless secondary bacterial infection is present in the underlying tissues. Meat quality is not affected.

Other Hyperkeratotic Conditions in Cervids

Other conditions causing hyperkeratotic-appearing lesions in deer include dermatophilosis (rain rot) caused by Dermatophilus congolensis, which produces crusting and scaling especially in wet conditions, and mange (sarcoptic or chorioptic) causing hair loss, thickened skin, and scaling. Lice infestations can also cause hyperkeratotic-appearing skin changes. Unlike camelids, true idiopathic zinc-responsive dermatosis is not a recognized condition in cervids.

Diagnostic Approach to Hyperkeratotic Lesions

Step-by-Step Diagnostic Protocol

• Complete history: Age, species, breed, diet, herd status, duration of lesions, previous treatments
• Physical examination: Distribution of lesions, presence/absence of pruritus, systemic signs
• Skin scrapings: Multiple deep scrapings to rule out mange (especially from interdigital spaces in camelids)
• Cytology: Impression smears for bacteria, yeast, and inflammatory cells
• Fungal culture: To rule out dermatophytosis
• Skin biopsy: Essential for definitive diagnosis - submit samples from active lesions
• Serum zinc (camelids): Use proper collection technique; remember normal levels don't exclude diagnosis
• Response to treatment: Trial of zinc supplementation may confirm diagnosis

Memory Aids for NAVLE Success

ZINC = "Zincy Is Not Contagious" Z - Zinc supplement treats it (1g sulfate or 2-4g methionine daily) I - Inguinal, axilla, medial thighs distribution N - Non-pruritic presentation C - Colored (dark) fleece predisposed

MUNGE = "Mostly Uncertain, Nasal-Gunk Eruption" M - Multiple potential triggers (bacterial, fungal, parasitic, viral) U - Underlying cause often unknown N - Nasal and perioral distribution G - Glucocorticoids may help (avoid in pregnant animals) E - Exclusion diagnosis (no definitive test)