A number of systemic diseases produce various lesions in the skin. Usually, the lesions are noninflammatory, and alopecia is common. In some instances, the cutaneous changes are characteristic of the particular disease. Often, however, the dermatosis is not obviously associated with the underlying condition and must be carefully differentiated from primary skin disorders.
Treatment depends on a specific etiologic diagnosis. Other than management of the primary disease, skin lesions usually need only palliative care (eg, control of scratching or moisturizing of the skin).
Nutritional Dermatoses in Animals
Nutritional dermatoses are associated with nutritional deficiency, especially of proteins, fats, minerals, some vitamins, and trace elements. However, these are uncommon in dogs and cats fed modern, balanced diets.
Arctic breeds (Siberian Huskies and Alaskan Malamutes) may develop a disease similar to parakeratosis Parakeratosis in Pigs Photograph of the ventral thorax and forelimbs of a pig with parakeratosis; there are many deep, dry, crusty lesions present. Photograph of a pig with parakeratosis lesions. Notice the lesions... read more 
in pigs, requiring additional zinc in their diet (elemental zinc at 2–3 mg/kg/day). Zinc-responsive dermatoses are associated with finely adherent scale, crusts, and erythema affecting the face, with a predominantly periocular and perioral distribution. These dermatoses, which have also been reported in cattle, sheep, goats, and llamas as well as in a dingo and a red wolf, may be associated with either a higher individual zinc requirement or a dietary deficiency. Dietary zinc deficiency may be precipitated by excessive consumption of calcium.
Skin Manifestations of Internal Organ Disorders in Animals
Dermatitis sometimes occurs in association with disorders of internal organs, such as the liver, kidneys, pancreas, or thymus.
Hepatic parenchymal dysfunction has been associated with superficial necrolytic dermatitis (hepatocutaneous syndrome Hepatocutaneous Syndrome in Small Animals Hepatocutaneous syndrome is a rare, chronic, progressive, and usually fatal disorder. Although typically associated with diabetes mellitus, the liver lesion is a severe, degenerative, glycogen-like... read more , diabetic dermatosis) in aged dogs and rarely in cats. Lesions are the result of hypoaminoacidemia secondary to liver disease.
The cutaneous lesions are commonly present on the face, genitals, and distal aspects of the extremities, severely affecting the footpads. Lesions include erythema, crusting, ulcerations, alopecia, and hyperkeratosis Hyperplastic and Seborrheic Syndromes in Animals Many anomalies affect keratinization; some are associated with hereditary hypotrichoses, whereas others are associated with systemic metabolic derangements. Those for which none of these associations... read more . The skin disease may precede the onset of clinical signs of the internal disease.
Histopathologic findings are diagnostic and include superficial perivascular to lichenoid dermatitis, with marked diffuse parakeratotic hyperkeratosis and striking inter- and intracellular edema limited to the upper half of the epidermis. Hyperglucagonemia has also been documented in dogs with this syndrome; however, dogs tend to have hepatic parenchymal dysfunction more commonly than glucagonomas.
In dogs, supportive treatment of superficial necrolytic dermatitis relies on IV or oral supplementation of amino acids or, if possible, surgical removal of the glucagonoma.
Skin fragility syndrome (excessive skin friability) in cats has been present in association with pancreatic Pancreatic Neoplasms in Dogs and Cats Exocrine pancreatic neoplasia is rare in dogs and cats, and most are secondary tumors. Clinical signs are nonspecific, leading to a late diagnosis in most cases. Diagnosis is primary by ultrasonography... read more or hepatic neoplasia Hepatic Neoplasia in Small Animals Lymphoma involving the liver and peripheral lymph nodes, spleen, and possibly bone marrow may have variable hepatic distribution (ie, portal regions, multifocal aggregates, sinusoidal, mass-like... read more , hepatic lipidosis Feline Hepatic Lipidosis Feline hepatic lipidosis (FHL), the most common acquired and potentially lethal feline liver disease, is a multifactorial syndrome. A primary disease process causing anorexia or food deprivation... read more , adrenal dysfunction, or excessive iatrogenic glucocorticoid administration. The skin will tear easily with minimal bleeding, which is very characteristic of this syndrome.
Cutaneous Manifestations of Internal Malignancy in Animals
Occasionally internal malignancies manifest as skin lesions. Pancreatic carcinoma Hepatic Neoplasia in Small Animals Lymphoma involving the liver and peripheral lymph nodes, spleen, and possibly bone marrow may have variable hepatic distribution (ie, portal regions, multifocal aggregates, sinusoidal, mass-like... read more (as well as bile duct carcinoma) has been associated with paraneoplastic dermatoses in cats, including crusting of the footpads and bilaterally symmetric alopecia affecting the ventrum and limbs. The hair is easily epilated, and alopecic areas are described as glistening.
Generalized large amounts of large, adhered scale (exfoliative dermatitis) and erythema have been identified in cats with a thymoma. This condition has also been identified without a thymoma present.(1–4 References A number of systemic diseases produce various lesions in the skin. Usually, the lesions are noninflammatory, and alopecia is common. In some instances, the cutaneous changes are characteristic... read more )
Cutaneous Manifestations of Renal Disease in Animals
A generalized nodular dermatofibrosis syndrome, Congenital and Hereditary Neoplasms and Hamartomas in Animals Congenital neoplasms are common in large animals. Mastocytosis, melanocytosis, cutaneous lymphosarcoma, and vascular hamartomas are found in calves. Melanocytomas may also arise shortly after... read more associated with renal cystadenomas, cystadenocarcinomas, or renal epithelial cysts, has been reported in German Shepherd Dogs and occasionally other breeds. Histologic examination of the skin nodules reveals dense collagen fibrosis.
Toxic Dermatosis in Animals
Poisoning by thallium sulfate (rat poisons Rodenticide Poisoning ), ergot Ergotism in Animals Ergotism in animals generally presents as lameness; necrosis of the tip of the tail, ears, and hoof tissue; and decay of the wattle, comb, beak, and feet in birds. Additional adverse effects... read more 
, mercury Mercury Poisoning , and iodides may cause toxic dermatosis, producing various skin changes. Hyperkeratosis in cattle can be caused by chlorinated naphthalene toxicity.
Dermatologic Manifestations of Endocrinopathies in Animals
In dogs, dermatosis can develop as a result of endocrine dysfunction The Endocrine System of Animals The endocrine system encompasses a group of tissues that release hormones into circulation. Hormones are signaling molecules that travel to targets distant from their site of production and... read more . Endocrinopathies are typically characterized by the following clinical signs:
Bilaterally symmetric truncal alopecia
Alopecia of the tail
Increased scale
Secondary pyoderma
Hypothyroidism
Dermatoses have been present in hypothyroidism Hypothyroidism in Animals Hypothyroidism is thyroid hormone deficiency. It is diagnosed by clinical features such as lethargy, weight gain, obesity, haircoat changes, and low serum thyroid hormone concentrations. Management... read more . In addition to the clinical signs typical of endocrinopathies, the skin is thickened and sometimes cool to the touch. Seborrhea oleosa may occur in some cases. The margins of the pinna may develop excess scale. In rare cases, cutaneous myxedema develops.
Hyperadrenocorticism
Hyperadrenocorticism Cushing Syndrome (Hyperadrenocorticism) Cushing syndrome refers to any cause of elevated cortisol concentrations. Pituitary-dependent hyperadrenocorticism (PDH; Cushing disease) is the most common form of hyperadrenocorticism and... read more 
is associated with the clinical signs typical of endocrinopathies, in addition to skin changes such as hyperpigmentation, alopecia, seborrhea, calcinosis cutis, and secondary pyoderma. In cats, the skin becomes extremely friable, causing skin fragility syndrome Defects of Structural Integrity Cats can be born with or may inherit several different kinds of skin abnormalities. Some inherited skin disorders can become visible weeks to months after birth. Most of these conditions are... read more .
For iatrogenic hyperadrenocorticism caused by topical glucocorticoid administration, switching treatment to a nonsteroidal-selective glucocorticoid receptor agonist, such as mapracorat, can be considered.
Hyperestrogenism
In males with Sertoli cell tumors, bilateral alopecia and occasional pruritus with a papular eruption may be present. Sexually intact female dogs with hormonal imbalances are usually pruritic and have a papular eruption, mammary tissue enlargement, and frequent estrous cycles. The skin lesions of both disorders may begin in the inguinal or flank region and progress cranially.
Dermatosis due to neutering is not common in dogs and cats; when it does occur, it is generally nonpruritic, with mild alopecia in the perineal or inguinal areas.
Exogenous estrogen administration has also been identified more recently as a cause of bilateral symmetrical alopecia. The source of exogenous estrogen may be estrogen cream applied to the skin of a person in close contact with the animal, allowing percutaneous absorption by the animal.
Other Endocrinopathies
Faulty production of hypophyseal hormones may rarely cause dermatoses, as in pituitary-dependent hyperadrenocorticism. Hypopituitarism is associated with alopecia, especially in the axillary regions and on the lateral thorax and abdomen.
In diabetes mellitus, pruritus and secondary infection sometimes occur, especially in cats with generalized Malasseziainfection.
Dermatosis Associated With Neuropathies in Animals
Rarely, underlying neurologic disorders, especially in dogs, may manifest as cutaneous lesions. These include sensory neuropathies in English Pointers and Longhaired Dachshunds, cauda equina syndrome, pseudorabies, neoplasia of peripheral nerves, and syringomyelia or Chiari-like malformation of Cavalier King Charles Spaniels.
Clinical signs generally include pruritus and scratching (sometimes phantom or air scratching in some cases of syringomyelia or Chiari-like malformation). Clinical signs also include pain in cauda equina syndrome and self-mutilation in the sensory neuropathies.
Key Points
Some systemic diseases have cutaneous manifestations; presentation of skin lesions and breed predispositions aid diagnosis of the primary disease.
Clinical signs will likely resolve with treatment of the primary disease, but symptomatic management of clinical signs can be beneficial in some cases.
Treatment depends on the specific etiologic diagnosis.
References
Brooks DG, Campbell KL, Dennis JS, et al. Pancreatic paraneoplastic alopecia in three cats. J Am Anim Hosp Assoc. 1994;30(6):557-563.
Tasker S, Griffon DJ, Nuttall TJ, Hill PB. Resolution of paraneoplastic alopecia following surgical removal of a pancreatic carcinoma in a cat. J Small Anim Pract. 1999;40(1):16-19. doi:10.1111/j.1748-5827.1999.tb03248.x
Pascal-Tenorio A, Olivry T, Gross TL, Atlee BA, Ihrke PJ. Paraneoplastic alopecia associated with internal malignancies in the cat. Vet Dermatol. 1997;8(1):47-52. doi:10.1111/j.1365-3164.1997.tb00263.x
Godfrey DR. A case of feline paraneoplastic alopecia with secondary Malassezia-associated dermatitis. J Small Anim Pract. 1998;39(8):394-396. doi:10.1111/j.1748-5827.1998.tb03739.x
Barrs VR, Martin P, France M, Mason K. What is your diagnosis? Feline paraneoplastic alopecia associated with pancreatic and bile duct carcinomas. J Small Anim Pract. 1999;40(12):559-596. doi:10.1111/j.1748-5827.1999.tb03021.x
