Extramammary Paget's disease is usually seen in isolation and is associated with an underlying invasive malignancy about 12% of the time. It is associated with an underlying adnexal malignancy about 24% of the time. Paget's disease of the breast is almost always associated with an underlying invasive malignancy, i.e. breast cancer (e.g. mammary ductal carcinoma).

Paget's disease of the vulva, a rare disease, may be a primary lesion or associated with adenocarcinoma originating from local organs such as the Bartholin gland, the urethra, or the rectum and thus be secondary. Patients tend to be postmenopausal.

Paget's disease of the penis may also be primary or secondary, and is even rarer than genital Paget’s disease in women. At least one case has been misdiagnosed as Bowen's disease. Isolated Paget's disease of the penis is extremely rare.

Most patients diagnosed with Paget's disease of the nipple are over age 50, but rare cases have been diagnosed in patients in their 20s. The average age at diagnosis is 62 for women and 69 for men. The disease is rare among both women and men.

The presence of three factors for the prognosis has been suggested, whether there is a palpable mass of the disease, whether lymph nodes are positive and whether there is an underlying malignant cancer.

If there is none of these, the five- and 10-year survival is 85% and 80% respectively, with adjuvant chemotherapy even 95% and 90%. If there is a palpable mass, it is 32% and 31% respectively, with adjuvant chemotherapy (40% and 35%).

Positive lymph-nodes have been positively associated with a palpable mass and affect the prognosis to be now just 28% survival after 10 years (vs 79% without palpable mass and without affected lymph-nodes). Involvement of the lymph nodes does not directly cause any harm, but is merely an indicator of systemic spread.

Furthermore, patients with an identifiable associated underlying breast tumor have a survival rate of 38-40% at five years and a survival rate of 22-33% at 10 years. The death rate of metastatic breast carcinoma in patients with mammary Paget's disease and underlying cancer is 61.3%, with a 10-year cumulative survival rate of 33%.

The exact cause of VIN is unknown. Studies are being done to determine the cause of VIN. The following factors have been associated with VIN:

- HPV (Human Papilloma Virus)

- HSV-2 (Herpes simplex Virus - Type 2)

- Smoking

- Immunosuppression

- Chronic vulvar irritation

- Conditions such as Lichen Sclerosus

White sponge nevus (WSN, or white sponge naevus, Cannon's disease, hereditary leukokeratosis of mucosa, white sponge nevus of Cannon, familial white folded dysplasia, or oral epithelial nevus), is an autosomal dominant condition of the oral mucosa (the mucous membrane lining of the mouth). It is caused by a mutations in certain genes coding for keratin, which causes a defect in the normal process of keratinization of the mucosa. This results in lesions which are thick, white and velvety on the inside of the cheeks within the mouth. Usually, these lesions are present from birth or develop during childhood. The condition is entirely harmless, and no treatment is required.

Perianal cellulitis (also known as "Perineal dermatitis," and "Streptococcal perianal disease") is a cutaneous condition that presents as sharply demarcated, bright, perianal erythema extending 2–3 cm around the anal verge.

There is no treatment, but because this is a benign condition with no serious clinical complications, prognosis is excellent.

Verruciform xanthoma is uncommon, with a female:male ratio of 1:1.1

Breast eczema (also known as "Nipple eczema") may affect the nipples, areolae, or surrounding skin, with eczema of the nipples being of the moist type with oozing and crusting, in which painful fissuring is frequently seen, especially in nursing mothers. It will often occur in pregnancy even without breast feeding.

Persisting eczema of the nipple in the middle-aged and elderly needs to be discussed with a doctor, as a rare type of breast cancer called Paget's disease can cause these symptoms.

Vaccinating girls with HPV vaccine before their initial sexual contact has been claimed to reduce incidence of VIN.

Anal dysplasia is most commonly linked to human papillomavirus (HPV), a usually sexually-transmitted infection. HPV is the most common sexually transmitted infection in the United States while genital herpes (HSV) was the most common sexually transmitted infection globally.

Can be caused by many things. A way to remember the causes is "PIG ON TAP"

Local factors-

- Occlusal Trauma

- Trauma

- Non-functional tooth

- Unopposed tooth (and impacted teeth, embedded teeth, teeth without antagonists)

Systemic factors-

- Idiopathic

- Pituitary Gigantism

- Paget's Disease

- Acromegaly

- Periapical granuloma

- Arthritis

- Calcinosis

- Rheumatic fever

It may be one of the complications of Paget's disease of bone in the form of generalized hypercementosis.

It may also be a compensatory mechanism in response to attrition to increase occlusal tooth height.

Porokeratosis is a specific disorder of keratinization that is characterized histologically by the presence of a cornoid lamella, a thin column of closely stacked, parakeratotic cells extending through the stratum corneum with a thin or absent granular layer.

A Paget's abscess, named by eminent British surgeon and pathologist Sir James Paget, is an abscess that recurs at the site of a former abscess which had resolved.

Paget's disease may be caused by a slow virus infection (i.e., paramyxoviridae) present for many years before symptoms appear. Associated viral infections include respiratory syncytial virus, canine distemper virus, and the measles virus. However, recent evidence has cast some doubt upon the measles association. Laboratory contamination may have played a role in past studies linking paramyxovirus (e.g. measles) to Paget's disease.

Verruciform xanthoma is an uncommon benign lesion that has a verruciform (wart-like) appearance, but it may appear polypoid, papillomatous, or sessile. The verruciform was first described by Shafer in 1971 on the oral mucosa. Usually found on the oral mucosa of middle-aged persons, verruciform xanthomas have also been reported on the scrotum and penis of middle-aged to elderly Japanese males. While the most common site is the oral mucosa, lesions that occur elsewhere usually arise on the perineum or on the skin with some predisposing factor, such as lymphedema or an epidermal nevus.

Anal dysplasia is a pre-cancerous condition which occurs when the lining of the anal canal undergoes abnormal changes. It can be classified as low-grade squamous intraepithelial lesions (LSIL) and high-grade squamous intraepithelial lesions (HSIL).

Most cases are not associated with symptoms, but people may notice lumps in and around the anus.

The disease is progressive and slowly worsens with time, although people may remain minimally symptomatic. Treatment is aimed at controlling symptoms, but there is no cure. Any bone or bones can be affected, but Paget's disease occurs most frequently in the spine, skull, pelvis, femur, and lower legs.

Osteogenic sarcoma, a form of bone cancer, is a rare complication of Paget's disease occurring in less than one percent of those affected. The development of osteosarcoma may be suggested by the sudden onset or worsening pain.

Erythroplasia of Queyrat is a squamous-cell carcinoma of the glans penis (head of the penis) or inner prepuce (foreskin) in males, and the vulvae in females. It mainly occurs in uncircumcised males, over the age of 40. Erythroplasia of Queyrat may also occur on the anal mucosa or the oral mucosa.

Some sources state that this condition is synonymous with Bowen's disease, however generally speaking Bowen's disease refers to carcinoma in situ of any location on the skin such as the lower leg. Like Bowen's disease, erythroplasia of Queyrat is associated with human papillomavirus 16 and is a precursor for invasive squamous-cell carcinoma.

It is named for French dermatologist Louis Queyrat (1856-1933), who was head of the dermatology service of l'Hôpital Ricord, a venereal hospital in Paris, now Hôpital Cochin.

Erythema dyschromicum perstans (EDP) (also known as ashy dermatosis, and dermatosis cinecienta) is an uncommon skin condition with peak age of onset being young adults, but it may also be seen in children or adults of any age. EDP is characterized by hyperpigmented macules that are ash-grey in color and may vary in size and shape. While agents such as certain medications, radiographic contrast, pesticides, infection with parasites, and HIV have been implicated in the occurrence of this disease, the cause of this skin disease remains unknown.

EDP initially presents as grey or blue-brown circumferential or irregularly shaped macules or patches that appear. While the lesions of EDP are generally non-elevated, they may initially have a slight raised red margin as they first begin to appear. These lesions usually arise in a symmetric distribution and involve the trunk, but also commonly spread to the face and extremities. EDP does not usually have symptoms beside the macules and patches of discolored skin; however, some itching in these areas may occur.

Because EDP is an uncommon disease of the skin, it is important to consider other skin diseases that may resemble erythema dyschromicum perstans, such as infectious diseases (i.e. leprosy or pinta), reaction to drugs, post inflammatory hyperpigmentation, or lichen planus pigmentosus.

There is no cure for EDP. While multiple various topical and systemic therapies have been tried, none have been consistently successful. In children, spontaneous resolution of EDP over the course of months to years is possible; however, this outcome is less likely if EDP presents in adulthood.

Surgery-associated ischemia may contribute inflammation at the anal transitional zone.

Patients whose cuffitis is refractory to mesalamine and/or corticosteroids should be evaluated for other disease in the cuff area, such as fistula or anastomotic leaks. Cuffitis that is refractory to medication can also be a sign of Crohn's disease of the pouch.

Chronic cuffitis can also contribute to the development of anastomotic stricture.

Cuffitis that is refractory, Crohn's-related, or is associated with surgical complications can contribute to pouch failure.

Hypercementosis is an idiopathic, non-neoplastic condition characterized by the excessive buildup of normal cementum (calcified tissue) on the roots of one or more teeth. A thicker layer of cementum can give the tooth an enlarged appearance, which mainly occurs at the apex or apices of the tooth.

Porokeratosis may be divided into the following clinical types:

- "Plaque-type porokeratosis" (also known as "Classic porokeratosis" and "Porokeratosis of Mibelli") is characterized by skin lesions that start as small, brownish papules that slowly enlarge to form irregular, annular, hyperkeratotic or verrucous plaques. Sometimes they may show gross overgrowth and even horn-like structures may develop. Skin malignancy, although rare, is reported from all types of porokeratosis. Squamous cell carcinomata have been reported to develop in Mibelli's type porokeratosis over partianal areas involving anal mucosa. This was the first report mentioning mucosal malignancy in any form of porokeratosis.

- "Disseminated superficial porokeratosis" is a more generalized processes and involves mainly the extremities in a bilateral, symmetric fashion. In about 50% of cases, skin lesions only develop in sun-exposed areas, and this is referred to as "disseminated superficial actinic porokeratosis"

- "Porokeratosis palmaris et plantaris disseminata" is characterized by skin lesions that are superficial, small, relatively uniform, and demarcated by a distinct peripheral ridge of no more than 1mm in height.

- "Linear porokeratosis" is characterized clinically skin lesions are identical to those of classic porokeratosis, including lichenoid papules, annular lesions, hyperkeratotic plaques with central atrophy, and the characteristic peripheral ridge.

- "Punctate porokeratosis" is a skin condition associated with either classic porokeratosis or linear porokeratosis types of porokeratosis, and is characterized by multiple, minute, and discrete punctate, hyperkeratotic, seed-like skin lesions surrounded by a thin, raised margin on the palms and soles.

- "Porokeratosis plantaris discreta" is a skin condition that occurs in adults, with a 4:1 female preponderance, characterized by a sharply marginated, rubbery, wide-based papules. It is also known as "Steinberg's lesion". It was characterized in 1970.

Angioid streaks are often associated with pseudoxanthoma elasticum (PXE), but have been found to occur in conjunction with other disorders, including Paget's disease, Sickle cell disease and Ehlers-Danlos Syndrome. These streaks can have a negative impact on vision due to choroidal neovascularization or choroidal rupture. Also, vision can be impaired if the streaks progress to the fovea and damage the retinal pigment epithelium.