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Response to disease
As it is so visible disease is readily apparent but there are a limited number of ways the skin reacts to disease. There may be hair loss, itch (pruritus), dandruff (scale), scabs (crusts), sores (papules, sinuses, pustules), changes in colour, lumps or discharges. Often more than one of these changes will be present and over the course of disease the mix of signs may change. For example a single lesion may start with redness and itch, then develop a swelling that is palpable this may then form a pimple which bursts forming a crust and scaling ring. If this process happens repeatedly in one are the skin may thicken become blackened and cause hair loss. So on differing occasions the same skin disease may present differently.
Diseases of the skin may be related to other organ systems or each other and a complex interplay of signs and diseases ensues causing confusion for the owners and difficulties for vets. It is therefore often necessary for many different diseases to be considered and ruled out before a final diagnosis to be made and correct treatment used.
Some specific areas of the skin have special functions and problems and will need to be approached in a different way to other parts of the skin including the ears, feet, claws and anal sacs.
Clinical signs affecting the skin
Hair loss (alopecia) Hair loss may be: focal (located in a single location), multifocal (with multiple single areas affected), regional or generalised. The pattern can be further described as being partial or total, symmetrical or irregular.
Alopecia can result from genetic factors (Chinese crested dogs, rex cats), hormonal (endocrine) diseases (hypothyroidism, hyperadrenocorticism, sex hormone abnormalities), hair follicle diseases (dermatophytosis, pyoderma, sebaceous adenitis) or it can be caused by hair breakage. Hair breakage may result from self-trauma (often associated with pruritus or pain) or hair abnormalities (i.e. colour dilution alopecia).
Itch (Pruritus) specific locations or generalised Many diseases present with itch (pruritus) as a major sign including parasitic diseases (fleas, lice, ticks, Notoedres cati, Cheyletiella, scabies), allergic diseases (food allergy, atopic dermatitis, contact hypersensitivity), infections (bacterial pyoderma, Malassezia dermatitis, dermatophytosis), autoimmune disease (i.e. pemphigus foliaceous,)
The pattern and severity of the pruritus and its relationship to other skin lesions will help your veterinarian select possible causes to be investigated. Often animals will have many different causes of pruritus affecting them at the same time having a cumulative effect, necessitating a series of diagnostic tests and therapeutic trials to clearly define the problem.
Dandruff (scale) Dandruff (Scale) is often present on animals with skin disease; it can either be primary sign of disease or secondary to other skin changes. It is a major presenting sign of Cheyletiella infestation and idiopathic seborrhoea but is more commonly a part of a mixed pattern of signs as seen with hypothyroidism or pyoderma.
Scabs (Crusts) >These are dried exudate and are usually present in association with papules, pustules, wounds or vesicles. They may consist of different cell types occasionally helping your veterinary pathologist to help make a diagnosis.
Sores/pimples (papules or pustules) Papules are small, raised lesions on the surface of the skin often associated with inflammatory cell infiltration. They are often seen with cases of pyoderma, flea allergic dermatitis and scabies.
Pustules are small well-demarcated elevations of the surface of the skin filled with pus. They are usually yellow or cream coloured but may have a green or red colour. Pustules are often very short lived and small quickly developing into papules, crusts and scale often leaving pigmented or erythematous areas on the skin. The depth and locations of pustules can be helpful when determining the likely cause. Your veterinarian may collect samples from pustules to help identify the cell type present and to look for microorganisms that may be present. Pustules are often seen in cases of pyoderma, demodecosis and pemphigus foliaceous.
Vesicles (blisters) Vesicles are well-demarcated elevations of the skin surface filled with clear fluid. These are rarely seen in domestic pets and rupture easily. Often the only sign seen is crust formation or shallow ulcers.
Pigment changes Changes to the colour of skin are commonly seen in skin disease of domestic animals. Skin may become red (erythema), dark (hyperpigmented) or light (hypopigmentation) Often erythema is seen with allergic (atopy, food hypersensitivity, contact hypersensitivity), parasitic (fleas, scabies, demodex), infectious (Malassezia, dermatophytosis, pyoderma) or even traumatic skin disease. Hyper pigmentation can be associated with any chronic inflammatory skin disease. Hypopigmentation is often associated with damage to the deeper tissues of the skin it is associated with pyoderma, uveo-dermatological syndrome, fungal infections, cutaneous lupus, vitiligo. The location, pattern and other lesions present may help your veterinarian limit the possible causes of pigment change.
Palpable lumps Often lumps are seen or palpated within the skin or just below the skin. These can be caused by inflammatory, cystic or neoplastic (cancerous) diseases. There may be associated hair loss (alopecia), inflammation, discharges, bleeding or discomfort. As there is potential for cancer in all lumps they should be investigated by your veterinarian. Determining the cause of lumps often requires biopsies to be collected and submitted for pathological analysis.
Wheals (hives, urticaria) These are inflammatory lumps that develop rapidly as fluid accumulates within the skin in response to skin insults or injuries. They can be associated with numerous diseases. Including allergies, insect bites or infections.
Ears
The skin of the ears poses some special problems. In healthy ears skin cells mature and migrate out of the ear canal as part of a normal process. When ears are inflamed there is an increase in production of oils and cells within the ears and an interruption of this normal process of cell migration and shedding. Often this will lead to secondary changes that perpetuate and exacerbate the original disease. There are several factors affecting ears that need to be considered in planning the approach to ear disease.
Several factors can predispose pets to ear disease including:
- Narrowed ear canals (common in Shar Pies)
- Floppy ears
- Hair growing within the ear canals (common in poodles and maltese terriers)
- Excessive moisture (humid environment, swimming)
- Trauma (vigorous cleaning, ear plucking, irritant topical therapy)
- Systemic illness
- Tumours
Several factors can cause ear disease to develop even in normal ears. These can be exacerbated by predisposing factors or occur without. These include:
- Ear mites (otodectes cyanotis)
- Other parasites (scabies, demodex, Notoedres cati, harvest mites)
- Allergies (atopic dermatitis, food hypersensitivity, contact dermatitis)
- Juvenile cellulitis
- Autoimmune diseases (Pemphigus foliaceous, SLE)
- Foreign bodies (grass awns, hairs)
- Hormonal diseases (hypothyroidism, hyperadrenocorticism, sex hormone imbalances)
- Keratinisation defects (idiopathic seborrhoea)
Once ears become inflamed they often develop secondary infections that also contribute to the inflammation within the ears. Examples include:
- Bacterial infections (pseudomonas, proteus, staphylococcus)
- Yeast infections (Malassezia)
Once inflammation has been present for some time other factors can develop that cause the otitis to persist and/or be resistant to therapy.
- Changes to ear canals associated with chronic disease. (Fibrosis, scarring, calcification, stenosis of canals, osteomyelitis)
- Otitis media
- Foreign bodies (dried medications or cellular debris)
Claws
Claws develop from special areas of the skin on the extremities of all digits. They grow principally from the coronary band (at the top of the nail) providing length with a contribution from the ventral sole (underneath the nail) that contributes to the thickness. The nail is formed from compressed skin cells fused to form a solid plate. It can grow at a rate of 1.9 mm per week but this reduces with age. Nails continually grow in a crescent shape and are worn down by normal activity. In some instances they are not worn and can grow sufficiently to penetrate the underside of the toe. There is a special fold of skin around the base of the claw called the ungual fold. This area, the claw itself and the underlying tissues can present some special difficulties in management and diagnosis of disease.
The nails can be traumatised by normal activity, particularly if allowed to grow excessively long or if other diseases affect their strength. Bacteria or fungi can infect the nails or the surrounding folds of skin. This is often a secondary effect of a more generalised systemic (hypothyroidism, hyperadrenocorticism, diabetes mellitus, auto immune disease, leishmaniasis) or skin disease (atopic dermatitis, cutaneous lupus, bullous pemphigoid, idiopathic seborrhoea, dermatophytosis, demodecosis, pemphigus foliaceous, Malassezia dermatitis, hook worm dermatitis). Occasionally all nails will be affected with no skin signs (i.e. symmetrical lupoid onychodystrophy). On occasions single claws will be affected by neoplasia underneath them and present with recurrent episodes of infection.
It is therefore essential in cases of recurrent or chronic nail disease to investigate the whole animal particularly the skin to get an accurate diagnosis. In some cases this will involve removing the last bone and nail of a digit for histopathology.
Anal sacs (anal glands)
Anal sacs are present in all domestic carnivores. They are paired sacs of skin located on either side of the anus at 4 and 8 O'clock. They are connected to narrow ducts leading to the outside. These sacs are lined with glands producing a pungent material that is usually brownish in colour. Wild carnivores use this material is to scent mark territories. Because of the narrow ducts any change in the nature of the secretions can cause these sacs can become blocked causing impaction. These glands can also become infected or abscessed. Dogs with anal sac disease often present with signs of self-trauma or hot spots around their rump or a history of "scooting"(dragging the anus along the ground in a sitting posture).
Often dogs or cats will initially have impacted anal sacs that need regular emptying and later develop recurrent or chronic infections. If the anal sacs become sufficiently damaged by these episodes they may have to be removed surgically. So it is important to treat these problems early and to differentiate infections needing specific therapy from impactions where the sacs just needing emptying.
Feet
The skin of the feet presents some specific difficulties. Not only are the feet favoured sites for skin diseases like atopic dermatitis, demodecosis, pemphigus foliaceous, Malassezia dermatitis, foreign body reactions, hepatocutaneous syndrome, zinc responsive dermatitis and naso-digital hyperkeratosis but they suffer secondary changes and infections in a similar way to ears. As the local environment between the toes and under the feet is folded with rubbing between adjacent areas of skin, small irritations can easily develop secondary infections and furunculosis. Animals can also easily traumatise their feet in a rough environment or by chewing. Often even when the infections and primary disease is treated there are secondary foreign body reactions to free hair shafts and scarring preventing normal healing. Occasionally chronic lesions that fail to respond to medical management will need surgery to remove foci of infection or scarring. It is therefore desirable to investigate the factors involved in foot disease early and apply prompt and appropriate treatment to prevent these changes.
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