Introduction

• Common presentation of a variety of dermatological problems.
• Cause: usually secondary to chronic dermatological disease.
• Primary pigmentary abnormalities rare.
• Usually of cosmetic concern only.
• Signs: may be associated with systemic disease.
• Diagnosis: most important reason for pursuing the underlying cause of changes in pigmentation is to determine if it is a manifestation of systemic disease.

Pathogenesis

Etiology

Hyperpigmentation - genetic

• Lentigo.
• Melanoderma and alopecia of the Yorkshire Terrier Skin: melanoderma and alopecia (Yorkshire Terrier).
• Nevi.
• Acanthosis nigricans Acanthosis nigricans.

Hyperpigmentation - acquired

• Post-inflammatory hypermelanosis.
• Demodicosis Skin: demodectic mange.
• Endocrinopathies Skin: hyposomatotropism.
• Neoplasia.

Hypopigmentation - genetic

• Piebaldism.
• Non-inflammatory nasal depigmentation Nasal depigmentation.
• Mucocutaneous hypopigmentation.
• Vitiligo  .
• Albinism.
• Waardenburg-Klein syndrome.
• Canine cyclic hematopoiesis Cyclic hematopoiesis.
• Tyrosinase deficiency.

Hypopigmentation - acquired

• Physical and chemical insults.
• Neoplasia.
• Idiopathic leucoderma and leucotrichia.
• Uveodermatologic syndrome.
• Systemic lupus erythematosus Systemic lupus erythematosus.
• Alopecia areata Skin: alopecia - overview.
• Discoid lupus erythematosus Skin: discoid lupus erythematosus.

Pigment changes/atypical pigmentation - genetic

• Canine cyclic hematopoiesis Cyclic hematopoiesis.
• Aquired aurotrichia of the Miniature Schnauzer Skin: aurotrichia (Miniature Schnauzer).

Pigment changes/atypical pigmentation - acquired

• Red hair from saliva or tear staining.
• Cutaneous flushing.

Nasal depigmentation

• Autoimmune diseases Skin: immunological disease - overview (Pemphigus foliaceus and erythematosus Skin: pemphigus foliaceus Skin: pemphigus erythematosus ).
• Allergic contact dermatitis Skin: allergic contact dermatitis.
• Nasal cutaneous lupus Skin: discoid lupus erythematosus.
• Drug reaction.
• Leishmaniosis Canine leishmaniosis.
• Mucocutaneous hypopigmentation.
• Mycosis (Aspergillosis Aspergillosis: disseminated ).
• Nasal actinic dermatitis.
• Neoplasia (squamous cell carcinoma Nasal planum: squamous cell carcinoma , epitheliotropic mucocutaneous T cell lymphoma).
• Non-inflammatory nasal depigmentation.
• Toxic epidermal necrolysis Skin: toxic epidermal necrolysis.
• Trauma - physical (X-rays, burns, cold, mechanical, surgical) and chemical insults.
• Uveodermatologic syndrome.
• Vasculitis Cutaneous vasculitis.
• Vitiligo.
• Zinc-responsive dermatosis Zinc toxicity.

Pathophysiology

• May be hereditary or acquired.
• May involve increased or decreased skin pigmentation.

• Unclear.
• Melanocytes produce melanin and are found in highest numbers in epidermis, mucus membrane epithelium and hair follicle epithelium.
• Melanin is incorporated into keratinocytes by pinocytosis.
• Clinical pigmentation is due to the amount and organisation of melanin-containing melanosomes in the keratinocytes.
• Control mechanisms include genetic factors and poorly understood local factors, eg ultraviolet light, inflammation, hormones.

Diagnosis