Autoimmune skin diseases occur when the immune system of an infected animal attacks its own skin.[1] In dogs, autoimmune skin diseases are usually not detected until visible symptoms appear, which differs from detection in humans who are able to verbally express their concerns.[2]Genetics, nutrition, and external environmental factors all collectively contribute to increasing the probability an autoimmune skin disease occurring.[3] The severity of symptoms varies based on the specific disease present and how far it has progressed. Diagnosis often requires the onset of visible symptoms and for a biopsy to be performed. For many diseases, the condition itself cannot be cured, but a veterinarian can prescribe medications and other forms of treatment to help manage the symptoms of the dog.[4]
The immune system has the ability to differentiate between the cells of the body and foreign cells. However, in dogs affected by an autoimmune disease, the immune system loses the ability to make this distinction, causing the immune system to attack the body.[5] Autoimmune diseases in the base layer of the epidermis are characterized by damage to the connective tissue and vesicle formation located below the epidermis layer and the dermis layer below it.[6][7] There are many autoimmune diseases, and they all vary in impact to the dog and progress at their own rates.[8]
Clinical symptoms
Pemphigus foliaceus in dogs: hair loss occurs, skin becomes red, and itchy.
Dogs suffering from autoimmune diseases of the skin may experience a variety of symptoms, including persistent itching and scratching, lesions, wounds, blisters, and other skin damage, as well as loss of skin pigment.[5] Two cases of autoimmune diseases that are often found include Discoid lupus erythematosus (DLE) and Pemphigus. DLE can develop into Systemic Lupus Erythematosus (SLE).[9] The initial stage of DLE is marked by a loss of skin pigment. The skin becomes red and sores appear on the nose. The palate can undergo erosion, ulceration, and injury to the nasal palate, as well as damage to the nostrils and the tissue around the eyes and ears. In chronic and severe cases, visual scar tissue often occurs.[9]
Most symptoms occur after the outer epidermis and inner dermis of the skin are affected by the disease. When this happens, the layers of the skin begin to separate, leading to painful lesions and pustules.[2] The compromised integrity of the skin barrier not only exacerbates the discomfort experienced by the dog, but also heightens the risk of secondary bacterial infections. The weakening of the skin's protective layers forms an environment susceptible to microbial infiltration, which could lead to severe complications. Intervening within an earlier time frame and targeted management strategies are essential to minimize further adverse effects.[10]
Another autoimmune skin disease which can occur in dogs is vitiligo. In addition to humans, vitiligo can be found in a variety of animals, including cats, horses, and dogs. Vitiligo is a type of autoimmune disease that damages melanocytes in the skin, lips, and oral cavity. Melanocytes are cells that contain pigments such as melanin. These pigments give rise to an organism's phenotype, which determines skin and hair color.[11] Melanocytes are also found in other parts of the body, such as the oral mucosa, eye, cochlea, and the meninges. In addition to vitiligo, there are other autoimmune diseases that target melanocytes, such as Vogt-Koyanagi-Harada (VKH) syndrome, and Uveodermatological (UDS) syndrome.[12] Vogt-Koyanagi-Harada syndrome is an autoimmune disease that affects the eyes. In addition to depigmentation of the skin, the disease is characterized by a combination of conditions, including uveitis, acute iridocyclitis, choroiditis, and retinal detachment.[13]
When pemphigus occurs in humans, the skin will begin to blister due to antibodies attacking the adhesive proteins in epidermal cells, which causes them to separate. Different types of pemphigus can be identified based on the depth of separation present in the skin. Many forms of pemphigus can be identified in dogs using methods similar to those employed for humans.[14]
Pemphigus vulgaris is rare in humans and animals, but is often fatal if left untreated. In dogs, the disease presents itself so similarly to the way it occurs in humans that dogs can be used as models for the disease in humans.[4] When the disease first begins to manifest itself, lesions are usually evident in the oral cavity of the dog.[9] Aside from these blisters, the dog may be mostly asymptomatic before the disease progresses further.[4] The blisters are easily ruptured and become painful upon doing so,[4] which can cause the dog to have difficulty eating.[15] As the disease progresses, the infected dog can become severely infirm, and may succumb to further infection.[4] Sometimes symptoms are characterized by lymphadenopathy, which involves loss of appetite, weakness, fever, and in rare cases, sepsis.[9]
Pemphigus foliaceus is the most common autoimmune skin disease in dogs, making up around one-third of all canine autoimmune disorders.[16] This disease usually affects areas of the ears and face.[9] Early symptoms are characterized by depigmentation of the nasal palate, dorsal cleft in the mouth, the ear, and the periocular area around the eye. Itching, pain, and weakness of the body have been observed in some cases. Other symptoms of Pemphigus foliaceus include hair loss, formation of pustules, and erosions with ulcers. These symptoms can appear on the dog's feet, groin area, and trunk if left untreated.[16]
Disease incidence process
The immune system functions in many ways to eliminate foreign substances and particles introduced to the body. This revolves around T-cell differentiation, where mature T-cells with receptors for non-self cells target foreign antigens and act with other cells to dispose of them.[17] There are two mechanisms of tolerance found in the immune system.[6] The first mechanism is positive selection by the thymus, where only T-cells are selected. T-cells recognize peptides in the Histocompatibility Complex (MHC).[6] The second mechanism is negative selection, where T-cells that recognize self-antigens with too high an affinity are removed through the process of apoptosis and are not allowed to enter the body's circulation.
Incidences of autoimmune skin diseases can vary based on several factors. Some of these factors include the breed, age, and sex of the dog, along with individual genetics and environmental factors.[3]
In terms of vitiligo, certain breeds of dogs have a higher chance of developing the disease based on their genetics. These breeds include Rottweilers, German Shepherds, Old English Sheepdogs, Doberman Pinchers, Dachshunds, and German Shorthaired Pointers.[citation needed] However, the exact prevalence of this disease in dogs is currently unknown, as it is likely under-reported.[2] Certain dog breeds that have been documented with Vogt-Koyanagi-Harada (VKH) syndrome include Akitas, Samoyeds, Irish Setters, Golden Retrievers, Saint Bernards, Australian Sheepdogs, and Shetland Sheepdogs.[13]
Pemphigus vulgaris can occur in any breed of dog irrespective of its sex or age.[4] However, it appears to occur more often in male dogs than females, which differs slightly from its occurrence in humans. In humans, women are more likely to be affected than men. In terms of age, the disease usually begins when the dog is at least five to seven years old. This correlates to the typical age in which it begins in humans as well, generally occurring in middle age.[15]
Diagnosis
Since many autoimmune skin diseases have similar symptoms and usually affect the oral cavity, a biopsy must often be performed in order to correctly diagnose the disease.[18] Due to the wide scale of clinical symptoms that can be present, along with the diverse variations of skin autoimmune dermatoses, a single symptom will more than likely not lead to a diagnosis. Instead, the results of the biopsy combined with the canine's history and other clinical signs can help in confirming the diagnosis of the disease. Breed predisposition and the age of the dog can also be indications of the various possibilities of autoimmune skin diseases.[19] Some common symptoms that can be used to lead to a confirmed diagnosis include alopecia, crusting, ulcerations, vasculitis, and many more.[19]
Histopathology evaluations can be done by extracting areas of the skin that show indications of being affected, such as taking biopsies of lesions, pustules, and sites of crustation. These tissue samples would then be typically examined under a microscope, where a clinician will form a conclusive diagnosis based on the observed cellular structures and abnormalities.[19] Additionally, other tests such as antinuclear antibody tests (ANA) and complete blood count with white blood cell differential tests can be used to gather more information.[20]
For Pemphigus vulgaris, after the skin begins to separate, Nikolsky's sign can be useful to help diagnose the disease. This involves placing pressure along the edge of a blister and observing if the skin separates further and if the blister increases in size.[21] However, to diagnose the disease with complete certainty, biopsies must be taken from the edge of the blisters. The tissue sample must then be analyzed using a direct immunofluorescence technique and analyzed microscopically. The direct immunofluorescence technique should be used instead of indirect, as the results may be inaccurate before the disease has progressed to a certain point.[4]
Treatment
For most autoimmune skin diseases, it is imperative to begin treatment as early as possible, as the progression of the disease can lead to severe complications and even death.[4] Treatment for many diseases usually involves the use of immunosuppressants such as glucocorticoids.[18] The immunosuppressants aid in suppressing the reaction of the immune system fighting against the body's healthy cells and tissues.[22] This is done by the inhibition of calcineurin, an enzyme that controls and activates T-cell production. Without the consistent production of T-cells, a decrease of autoimmune activity can be observed, leading to less severe symptoms and potential remission of autoimmune diseases.[23]
When treatment is first started for Pemphigus vulgaris, the dog will usually be given the corticosteroidprednisone for a limited time. This will be administered orally, and the amount given can vary between 1.5 and 13.3 milligrams for every kilogram of the dog's weight. This amount will continue until symptoms begin to subside. Afterward the dose will be lowered, and other medications will be used. The condition cannot be cured, so the dog will require immunosuppressants and steroids for the duration of its lifespan. The specific immunosuppressants used generally include cyclophosphamide, methotrexate, or azathioprine. Antibiotics may also be used to help reduce the risk of infection.[4]
Vitiligo is a chronic autoimmune disorder that causes patches of skin to lose pigment or color. The cause of vitiligo is unknown, but it may be related to immune system changes, genetic factors, stress, or sun exposure. Treatment options include topical medications, light therapy, surgery and cosmetics. The condition can show up on any skin type as a light peachy color and can appear on any place on the body in all sizes. The spots on the skin known as vitiligo are also able to “change” as spots lose and regain pigment; they will stay in relatively the same areas but can move over time and some big patches can move through the years but never disappear overnight.
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an "autoimmune disease". Prominent examples include celiac disease, diabetes mellitus type 1, Henoch–Schönlein purpura, systemic lupus erythematosus, Sjögren syndrome, eosinophilic granulomatosis with polyangiitis, Hashimoto's thyroiditis, Graves' disease, idiopathic thrombocytopenic purpura, Addison's disease, rheumatoid arthritis, ankylosing spondylitis, polymyositis, dermatomyositis, and multiple sclerosis. Autoimmune diseases are very often treated with steroids.
Addison's disease, also known as primary adrenal insufficiency, is a rare long-term endocrine disorder characterized by inadequate production of the steroid hormones cortisol and aldosterone by the two outer layers of the cells of the adrenal glands, causing adrenal insufficiency. Symptoms generally come on slowly and insidiously and may include abdominal pain and gastrointestinal abnormalities, weakness, and weight loss. Darkening of the skin in certain areas may also occur. Under certain circumstances, an adrenal crisis may occur with low blood pressure, vomiting, lower back pain, and loss of consciousness. Mood changes may also occur. Rapid onset of symptoms indicates acute adrenal failure, which is a clinical emergency. An adrenal crisis can be triggered by stress, such as from an injury, surgery, or infection.
A desmosome, also known as a macula adherens, is a cell structure specialized for cell-to-cell adhesion. A type of junctional complex, they are localized spot-like adhesions randomly arranged on the lateral sides of plasma membranes. Desmosomes are one of the stronger cell-to-cell adhesion types and are found in tissue that experience intense mechanical stress, such as cardiac muscle tissue, bladder tissue, gastrointestinal mucosa, and epithelia.
Pemphigus is a rare group of blistering autoimmune diseases that affect the skin and mucous membranes. The name is derived from the Greek root pemphix, meaning "blister".
Skin disorders are among the most common health problems in dogs, and have many causes. The condition of a dog's skin and coat is also an important indicator of its general health. Skin disorders of dogs vary from acute, self-limiting problems to chronic or long-lasting problems requiring life-time treatment. Skin disorders may be primary or secondary in nature, making diagnosis complicated.
Staphylococcal scalded skin syndrome (SSSS) is a dermatological condition caused by Staphylococcus aureus.
Bullous pemphigoid is an autoimmune pruritic skin disease that typically occurs in people aged over 60, that may involve the formation of blisters (bullae) in the space between the epidermal and dermal skin layers. It is classified as a type II hypersensitivity reaction, which involves formation of anti-hemidesmosome antibodies, causing a loss of keratinocytes to basement membrane adhesion.
Necrotizing meningoencephalitis (NME) is a fatal inflammatory central nervous system (CNS) disorder in dogs, where an extensive cerebral necrosis is associated with a multifocal, non-suppurative meningoencephalitis of the neuro cortex. It was originally identified and recorded in the 1960s in pure breed pugs, with which this disease is nowadays mostly associated with, occurring essentially in small breed dogs ranging from six months to seven years of age. It causes intense necrotizing inflammatory lesions in the brain stem and Cerebellum. The cause is still unclear. The pathogen that triggers the disease and contributes to its development has not yet been identified. It is presumed to have a multifactorial, heritable, autoimmune etiology. The process is rapidly progressive, culminating in status epilepticus and ending fatally for the dog.
Discoid lupus erythematosus (DLE) is an uncommon autoimmune disease of the basal cell layer of the skin. It occurs in humans and cats, more frequently occurring in dogs. It was first described in dogs by Griffin and colleagues in 1979. DLE is one form of cutaneous lupus erythematosus (CLE). DLE occurs in dogs in two forms: a classical facial predominant form or generalized with other areas of the body affected. Other non-discoid variants of CLE include vesicular CLE, exfoliative CLE and mucocutaneous CLE. It does not progress to systemic lupus erythematosus (SLE) in dogs. SLE can also have skin symptoms, but it appears that the two are either separate diseases. DLE in dogs differs from SLE in humans in that plasma cells predominate histologically instead of T lymphocytes. Because worsening of symptoms occurs with increased ultraviolet light exposure, sun exposure most likely plays a role in DLE, although certain breeds (see below) are predisposed. After pemphigus foliaceus, DLE is the second most common autoimmune skin disease in dogs.
Pemphigus vulgaris is a rare chronic blistering skin disease and the most common form of pemphigus. Pemphigus was derived from the Greek word pemphix, meaning blister. It is classified as a type II hypersensitivity reaction in which antibodies are formed against desmosomes, components of the skin that function to keep certain layers of skin bound to each other. As desmosomes are attacked, the layers of skin separate and the clinical picture resembles a blister. These blisters are due to acantholysis, or breaking apart of intercellular connections through an autoantibody-mediated response. Over time the condition inevitably progresses without treatment: lesions increase in size and distribution throughout the body, behaving physiologically like a severe burn.
Hailey–Hailey disease (HHD), or familial benign chronic pemphigus or familial benign pemphigus, was originally described by the Hailey brothers in 1939. It is a genetic disorder that causes blisters to form on the skin.
Desmoglein-1 is a protein that in humans is encoded by the DSG1 gene. Desmoglein-1 is expressed everywhere in the skin epidermis, but mainly it is expressed in the superficial upper layers of the skin epidermis.
Discoid lupus erythematosus is the most common type of chronic cutaneous lupus (CCLE), an autoimmune skin condition on the lupus erythematosus spectrum of illnesses. It presents with red, painful, inflamed and coin-shaped patches of skin with a scaly and crusty appearance, most often on the scalp, cheeks, and ears. Hair loss may occur if the lesions are on the scalp. The lesions can then develop severe scarring, and the centre areas may appear lighter in color with a rim darker than the normal skin. These lesions can last for years without treatment.
An autoimmune disease is a condition that results from an anomalous response of the adaptive immune system, wherein it mistakenly targets and attacks healthy, functioning parts of the body as if they were foreign organisms. It is estimated that there are more than 80 recognized autoimmune diseases, with recent scientific evidence suggesting the existence of potentially more than 100 distinct conditions. Nearly any body part can be involved.
Pemphigus foliaceus is an autoimmune blistering disease of the skin. Pemphigus foliaceus causes a characteristic inflammatory attack at the subcorneal layer of epidermis, which results in skin lesions that are scaly or crusted erosions with an erythematous (red) base. Mucosal involvement is absent even with widespread disease.
Paraneoplastic pemphigus (PNP) is an autoimmune disorder stemming from an underlying tumor. It is hypothesized that antigens associated with the tumor trigger an immune response resulting in blistering of the skin and mucous membranes.
Sebaceous adenitis in an uncommon skin disease found in some breeds of dog, and more rarely in cats, rabbits and horses. characterised by an inflammatory response against the dog's sebaceous glands, which can lead to the destruction of the gland. It was first described in veterinary literature in the 1980s.
Immune-mediated thrombocytopaenia (IMT) is a disease common in dogs and rare in cats. The disease is characterised by a low platelet count caused by destruction of the platelets from the immune system. IMT is the most common cause of thrombocytopaenia in dogs.
References
↑ Gershwin, Laurel J. (March 2018). "Current and Newly Emerging Autoimmune Diseases". Veterinary Clinics of North America: Small Animal Practice. 48 (2): 323–338. doi:10.1016/j.cvsm.2017.10.010. PMID29248206.
1 2 Gershwin, Laurel J. (May 2010). "Autoimmune Diseases in Small Animals". Veterinary Clinics of North America: Small Animal Practice. 40 (3): 439–457. doi:10.1016/j.cvsm.2010.02.003. PMID20471527.
1 2 3 Papadogiannakis (E. ι. παπαδογιαννακης), E. I. (29 November 2017). "Contemporary aspects on the immunopathogenesis of autoimmune diseases of the epidermal basement membrane in the dog". Journal of the Hellenic Veterinary Medical Society. 56 (1): 27. doi:10.12681/jhvms.15066.
1 2 Bizikova, Petra; Linder, Keith E.; Anderson, Jamie G. (17 April 2023). "Erosive and ulcerative stomatitis in dogs and cats: which immune-mediated diseases to consider?". Journal of the American Veterinary Medical Association. 261 (S1): S48–S57. doi:10.2460/javma.22.12.0573. PMID37059419.
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