Intrauterine epidermal necrosis is a cutaneous condition that is rapidly fatal, characterized by skin erosions and ulcerations only.

NL/NLD most frequently appears on the patient's shins, often on both legs, although it may also occur on forearms, hands, trunk, and, rarely, nipple, penis, and surgical sites. The lesions are often asymptomatic but may become tender and ulcerate when injured. The first symptom of NL is often a "bruised" appearance (erythema) that is not necessarily associated with a known injury. The extent to which NL is inherited is unknown.

NLD appears as a hardened, raised area of the skin. The center of the affected area usually has a yellowish tint while the area surrounding it is a dark pink. It is possible for the affected area to spread or turn into an open sore. When this happens the patient is at greater risk of developing ulcers. If an injury to the skin occurs on the affected area, it may not heal properly or it will leave a dark scar.

NME features a characteristic skin eruption of red patches with irregular borders, intact and ruptured vesicles, and crust formation. It commonly affects the limbs and skin surrounding the lips, although less commonly the abdomen, perineum, thighs, buttocks, and groin may be affected. Frequently these areas may be left dry or fissured as a result. All stages of lesion development may be observed synchronously. The initial eruption may be exacerbated by pressure or trauma to the affected areas.

Necrobiosis lipoidica is a necrotising skin condition that usually occurs in patients with diabetes mellitus but can also be associated with rheumatoid arthritis. In the former case it may be called necrobiosis lipoidica diabeticorum (NLD). NLD occurs in approximately 0.3% of the diabetic population, with the majority of sufferers being women (approximately 3:1 females to males affected).

The severity or control of diabetes in an individual does not affect who will or will not get NLD. Better maintenance of diabetes after being diagnosed with NLD will not change how quickly the NLD will resolve.

Pain may be the first noticed symptom. People with lipodermatosclerosis have tapering of their legs above the ankles, forming a constricting band resembling an inverted champagne bottle. In addition, there may be brownish-red pigmentation and induration.

Initially red to pink, flat spots (formally, "macules") and raised bumps (formally, "papules") may be seen on the skin.

Once fully developed, the classic appearance is "non-blanching, palpable purpura". This appears as deep red to purple spots that feel raised to the touch. Purpura refers to the red-purple discolored spots, while palpable implies that these spots can be felt as raised from the surrounding skin. Additionally, when gently pressed, the color does not fade to a lighter color ("non-blanching"). The red-purple color of the lesions is due to the inflammation in the blood vessels causing red blood cells to escape into the dermis skin layer.

Small fluid-filled blisters (or "vesicles"), pus-filled bumps resembling a pimple (or "pustules"), or shallow ulcers may also develop but are less common.

The location of skin lesions varies but are most commonly found symmetrically below the waist, primarily on the buttocks and legs. Other distributions include localized areas on the upper body or over several areas of the body.

With treatment, the lesions typically resolve in weeks to months and leave behind flat spots that are darker than the surrounding skin. (see "Postinflammatory hyperpigmentation" on "Hyperpigmentation")

A portion of cases may be persistent or recurrent. This tends to occur when the vasculitis is associated with chronic conditions such as connective tissue diseases.

Dermatitis gangrenosa (also known as "Gangrene of the skin") is a cutaneous condition caused by infection by Clostridium resulting in a necrosis and sloughing of the skin.

In most cases skin lesions do not cause symptoms, however itching, burning, or pain may occur.

Frequently reported symptoms include mild fever, muscle pain, joint pain, or an overall feeling of discomfort. Additional symptoms depend on the cause of the vasculitis and if other organ systems are involved. For example, if the vasculitis is a manifestation of Henoch-Schönlein purpura, individuals may also experience abdominal pain or blood in the urine.

The histopathologic features of NME are nonspecific and include:

- epidermal necrosis

- subcorneal pustules

- confluent parakeratosis, epidermal hyperplasia, and marked papillary dermal hyperplasia in a psoriasiform pattern

- angioplasia of papillary dermis

- suppurative folliculitis

The vacuolated, pale, swollen epidermal cells and necrosis of the superficial epidermis are most characteristic. Immunofluorescence is usually negative.

Fever and a non specific skin eruption – with reddening (erythema) and swelling (oedema) of the skin – are the most common symptoms of NEH. Patients usually present with the skin eruption 1-2 weeks after use of the cytotoxic drug. Sometimes, the skin eruption can be painful. Skin eruptions can be located on the extremities, trunk, and face. Severe lesions are rare, and can mimic cellulitis. Generalised lesions resembling erythema multiforme have been reported.

Sclerema neonatorum is a rare and severe skin condition that is characterized by diffuse hardening of the subcutaneous tissue with minimal inflammation. It usually affects premature, ill newborns. Prognosis is poor.

Minimal inflammation helps distinguish sclerema neonaturum from subcutaneous fat necrosis of the newborn.

Non-vasculitis forms of panniculitis that may occur include:

- "Cytophagic Histiocytic Panniculitis" was first described in 1980 by Winkelmann as a chronic histiocytic disease of the subcutaneous adipose tissue, which is characterized clinically by tender erythematous nodules, recurrent high fever, malaise, jaundice, organomegaly, serosal effusions, pancytopenia, hepatic dysfunction and Coagulation abnormalities. CHP may occur either isolated or as part of cutaneous manifestations of Hemophagocytic syndrome (HPS). CHP is a rare and often fatal form of panniculitis with multisystem involvement. But it can also present in a benign form involving only the subcutaneous tissue, thus having a broad clinical spectrum.

- "Traumatic panniculitis" is a panniculitis that occurs following trauma to the skin.

- "Cold panniculitis" is a panniculitis occurring after exposure to cold, most often seen in infants and young children. This condition has been described in children who suck ice or popsicles, and therefore is sometimes referred to as "popsicle panniculitis." The term was coined when a patient with a rash of unknown origin on her cheek was taken to a dermatologist.

- "Gouty panniculitis" is a panniculitis caused by deposition of uric acid crystals in gout.

- "Pancreatic panniculitis" (also known as "Enzymatic panniculitis," "Pancreatic fat necrosis," and "Subcutaneous fat necrosis") is a panniculitis most commonly associated with pancreatic carcinoma, and more rarely with anatomic pancreatic abnormalities, pseudocysts, or drug-induced pancreatitis.

- "Factitial panniculitis" is a panniculitis that may be induced by the injection of organic materials, povidone, feces, saliva, vaginal fluid, and oils.

Erythema nodosum is a form of panniculitis characterised by tender red nodules, 1–10 cm, associated with systemic symptoms including fever, malaise, and joint pain. Nodules may become bluish-purple, yellowing, and green, and subside over a period of 2–6 weeks without ulcerating or scarring. Erythema nodosum is associated with infections, including Hepatitis C, EBV and tuberculosis, Crohn's disease and sarcoidosis, pregnancy, medications including sulfonamides, and some cancers, including Non-Hodgkin lymphoma and pancreatic cancer.

Lipodermatosclerosis (also known as "chronic panniculitis with lipomembranous changes", "hypodermitis sclerodermiformis", "sclerosing panniculitis", and "stasis panniculitis") is a skin and connective tissue disease. It is a form of lower extremity panniculitis, an inflammation of the layer of fat under the epidermis.

Ecthyma gangrenosum is a type of skin lesion characterized by vesicles or blisters which rapidly evolve into pustules and necrotic ulcers with undermined tender erythematous border. "Ecthyma" means a pus forming infection of the skin with an ulcer, "gangrenosum" means the gangrene or necrosis. It is the pathognomonic of "Pseudomonas aeruginosa" bacteremia. "Pseudomonas aeruginosa" is a gram negative, aerobic, coccobacillus bacterium.

This type of skin lesion was first described in association with "Pseudomonas aeruginosa" by L. Barker in 1897. It was given the name "ecthyma gangrenosum" by Hitschmann and Kreibich.

It mostly occurs in patients with underlying immunocompromised conditions (e.g. Malignancy). Although most cases are found in "Pseudomonas aeruginosa" infection, there are recent reports of this skin lesion associated with other microorganisms, such as "Escherichia coli, Citrobacter freundii, Klebsiella pneumonia", various other Pseudomonas species, and "Morganella morganii."

The primary skin lesion usually starts with a macule that is painless, round and erythematous. Then, it develops into a pustule, and then a bulla with central hemorrhagic focus. The bullae progresses into an ulcer which extends laterally. Finally it becomes a gangrenous ulcer with central black eschar surrounded by erythematous halo.

The lesion may be single or multiple. They are most commonly seen in perineum and under arm pit. However, it can occur in any part of the body.

Chronic inflammation can cause long term lymphatic obstruction. Typically, patients have disorders that present local nodes, primary lymphedema and chronic venous insufficiency. Erysipelas and trauma are major risk factors. Lymphatic edema can be developed in many acral cases accompanied by a thickening of the folds of the skin, hyperkeratosis and papillomatosis. Chronic venous edema is only partially reversible and soon becomes hard, especially confirming tenderness. All structures of the skin are affected. Dilated dermal lymphatic vessels with consequent superior organization and fibrosis result in papillomatosis. As dermal lymphatic stasis progreses, these skin changes become more marked and known as elephantiasis. Occasionally, tissue fibrosis and thickening may become so marked in the later stages of lymphedema that pitting is absent. Recurrent cellulitis, erysipelas and dermato-LAM-adenitis are complications of chronic lymphedema.

Stasis Papillomatosis is similar to AGEP (Acute generalized exanthematous pustulosis) from pustular psoriasis; criteria for histopathologic distinction have been proposed: papillary edema, vasculitis, exocytosis of eosinophils and single-cell necrosis of keratinocytes in AGEP and acanthosis and papillomatosis in pustular psoriasis.

An example that illustrates the difference between SP and Stasis Papillomatosis and the histology diagnosis is … “a markedly obese, 41-year-old Japanese man who had suffered from psoriasis vulgaris for several years visited hospital with elephantiasis-like swelling of his lower legs of three months' duration. His right lower leg showed marked papillomatosis with thick scales, and the left lower leg was eroded and papillomatous. Although direct lymphography of his lower extremities showed no abnormality, indirect lymphography revealed local lymphatic damage in the involved skin”. Histological examination showed hyperkeratosis, marked papillomatosis, proliferation of capillaries in the upper dermis, and lymphectasia in the lower dermis. It was suspected that obesity and the preceding psoriatic lesions caused local lymphatic disturbances, followed by the development of stasis papillomatosis.

PAPA syndrome usually begins with arthritis at a young age, with the skin changes more prominent from the time of puberty.

The arthritis is the predominant feature, noted by its juvenile onset and destructive course. Individuals often recall episodes of arthritis precipitated by a traumatic event. With repeated episodes the joints become damaged with multiple joint replacements required. Hopefully, with improved treatment options, the damage will be limited in new cases.

Pyoderma gangrenosum is variably expressed, which means that it is not always present in all individuals with the disease. It presents as poorly healing ulcers with undermined edges. Pathergy is an important feature (this term refers to the tendency of ulcers to arise at points of injury). There are reports of lesions developing at the site of a joint replacement wound, central venous line and intravenous drip insertion.

Acne affects most individuals with PAPA syndrome but to a variable degree. It is usually of a severe nodulocystic type which if untreated results in scarring.

Neutrophilic eccrine hidradenitis (NEH) usually is a cutaneous complication of chemotherapy, but it can also occur for other reasons. It consists of fever and non specific skin lesions. It is rare, and self-limited.

Different types of discharges from ulcer are:

- Serous, usually seen in healing ulcer

- Purulent, seen in infected ulcer. Yellow creamy discharge is observed in staphylococcal infection; bloody opalescent discharge in streptococcal infection, while greenish discharge is seen in pseudomonas ulcer

- Bloody (sanguineous), usually seen in malignant ulcers and in healing ulcers with healthy granulation tissue

- Seropurulent

- Serosanguinous

- Serous with sulphur granules, seen in actinomycosis

- Yellowish, as seen in tuberculous ulcer

Hidradenitis suppurativa is a chronic inflammatory skin condition, considered a member of the acne family of disorders. It is sometimes called acne inversa. The first signs of HS are small bumps on the skin that resemble pimples, cysts, boils, or folliculitis. As the disease progresses and abscesses reoccur, they become larger and more painful; eventually tunnels of scar tissue connect the lesions. These lesions may open up if they become too enlarged and drain bloodstained pus. One risk factor is age; HS usually first appears during the 20s and early 30s. The condition is much more common in women than in men but is usually more serious and debilitating in men. Other associated conditions include obesity, diabetes, metabolic syndrome, arthritis, acne, and other inflammatory disorders. Early diagnosis of this disease is very important to decrease the number of flares, pain, and discomfort.

Blue nevi may be divided into the following types:

- A "patch blue nevus" (also known as an "acquired dermal melanocytosis", and "dermal melanocyte hamartoma") is a cutaneous condition characterized by a diffusely gray-blue area that may have superimposed darker macules.

- A "blue nevus of Jadassohn–Tièche" (also known as a "common blue nevus", and "nevus ceruleus") is a cutaneous condition characterized by a steel-blue papule or nodule.

- A "cellular blue nevus" is a cutaneous condition characterized by large, firm, blue or blue-black nodules.

- An "epithelioid blue nevus" is a cutaneous condition most commonly seen in patients with the Carney complex.

- A "deep penetrating nevus" is a type of benign melanocytic skin tumor characterized, as its name suggests, by penetration into the deep dermis and/or subcutis. Smudged chromatic is a typical finding. In some cases mitotic figures or atypical melanocytic cytology are seen, potentially mimicking a malignant melanoma. Evaluation by an expert skin pathologist is advisable in some cases to help differentiate from invasive melanoma.

- An "amelanotic blue nevus" (also known as a "hypomelanotic blue nevus") is a cutaneous condition characterized by mild atypia and pleomorphism.

- A "malignant blue nevus" is a cutaneous condition characterized by a sheet-like growth pattern, mitoses, necrosis, and cellular atypia.

Skin ulcers appear as open craters, often round, with layers of skin that have eroded. The skin around the ulcer may be red, swollen, and tender. Patients may feel pain on the skin around the ulcer, and fluid may ooze from the ulcer. In some cases, ulcers can bleed and, rarely, patients experience fever. Ulcers sometimes seem not to heal; healing, if it does occur, tends to be slow. Ulcers that heal within 12 weeks are usually classified as acute, and longer-lasting ones as chronic.

Ulcers develop in stages. In stage 1 the skin is red with soft underlying tissue. In the second stage the redness of the skin becomes more pronounced, swelling appears, and there may be some blisters and loss of outer skin layers. During the next stage, the skin may become necrotic down through the deep layers of skin, and the fat beneath the skin may become exposed and visible. In stage 4, deeper necrosis usually occurs, the fat underneath the skin is completely exposed, and the muscle may also become exposed. In the last two stages the sore may cause a deeper loss of fat and necrosis of the muscle; in severe cases it can extend down to bone level, destruction of the bone may begin, and there may be sepsis of joints.

Chronic ulcers may be painful. Most patients complain of constant pain at night and during the day. Chronic ulcer symptoms usually include increasing pain, friable granulation tissue, foul odour, and wound breakdown instead of healing. Symptoms tend to worsen once the wound has become infected.

Venous skin ulcers that may appear on the lower leg, above the calf or on the lower ankle usually cause achy and swollen legs. If these ulcers become infected they may develop an unpleasant odour, increased tenderness and redness. Before the ulcer establishes definitively, there may be a dark red or purple skin over the affected area as well as a thickening, drying, and itchy skin.

Although skin ulcers do not seem of great concern at a first glance, they are worrying conditions especially in people suffering from diabetes, as they are at risk of developing diabetic neuropathy.

Ulcers may also appear on the cheeks, soft palate, the tongue, and on the inside of the lower lip. These ulcers usually last from 7 to 14 days and can be painful.

Hidradenitis is any disease in which the histologic abnormality is primarily an inflammatory infiltrate around the eccrine glands. This group includes neutrophilic eccrine hidradenitis and recurrent palmoplantar hidradenitis.

It can also be defined more generally as an inflammation of sweat glands.

Hidradenitis suppurativa is a chronic cutaneous condition originally thought to be primarily characterized by suppurative inflammation of the apocrine sweat glands. However, recent evidence supports that the primary event is follicular hyperkeratosis and obstruction.