Sarcoidosis involves the skin in between 9 and 37% of persons and is more common in African Americans than in European Americans. The skin is the second most commonly affected organ after the lungs. The most common lesions are erythema nodosum, plaques, maculopapular eruptions, subcutaneous nodules, and lupus pernio. Treatment is not required, since the lesions usually resolve spontaneously in two to four weeks. Although it may be disfiguring, cutaneous sarcoidosis rarely causes major problems. Sarcoidosis of the scalp presents with diffuse or patchy hair loss.

Ulcerative sarcoidosis is a cutaneous condition affecting roughly 5% of people with sarcoidosis.

Annular sarcoidosis is a cutaneous condition characterized by papular skin lesions arranged in annular

patterns, usually with a red-brown hue.

The frequency of cardiac involvement varies and is significantly influenced by race; in Japan more than 25% of persons with sarcoidosis have symptomatic cardiac involvement, whereas in the US and Europe only about 5% of cases present with cardiac involvement. Autopsy studies in the US have revealed a frequency of cardiac involvement of about 20–30%, whereas autopsy studies in Japan have shown a frequency of 60%. The presentation of cardiac sarcoidosis can range from asymptomatic conduction abnormalities to fatal ventricular arrhythmia. Conduction abnormalities are the most common cardiac manifestations of sarcoidosis in humans and can include complete heart block. Second to conduction abnormalities, in frequency, are ventricular arrhythmias, which occurs in about 23% of persons with cardiac involvement. Sudden cardiac death, either due to ventricular arrhythmias or complete heart block is a rare complication of cardiac sarcoidosis. Cardiac sarcoidosis can cause fibrosis, granuloma formation, or the accumulation of fluid in the interstitium of the heart, or a combination of the former two.

Morpheaform sarcoidosis is a very rare cutaneous condition characterized by specific cutaneous skin lesions of sarcoidosis accompanied by substantial fibrosis, simulating morphea.

Erythrodermic sarcoidosis is a cutaneous condition and very rare form of sarcoidosis.

Hypopigmented sarcoidosis is a cutaneous condition characterized by areas of hypopigmented skin. It is usually diagnosed in darkly pigmented races and may be the earliest sign of sarcoidosis.

Papular sarcoid is a cutaneous condition characterized by papules, which are the most common morphology of cutaneous sarcoidosis.

Ichthyosiform sarcoidosis is a cutaneous condition resembling ichthyosis vulgaris or acquired ichthyosis, with fine scaling usually on the distal extremities, by caused by sarcoidosis.

Necrotizing granulomas can develop in patients with rheumatoid arthritis, typically manifesting as bumps in the soft tissues around the joints (so-called rheumatoid nodules) or in the lungs.

Certain inflammatory diseases are characterised by a combination of granulomatous inflammation and vasculitis (inflammation of the blood vessels). Both the granulomas as well as the vasculitis tend to occur in association with necrosis. Classic examples of such diseases include granulomatosis with polyangiitis (GPA; previously referred to by the eponym Wegener's granulomatosis) and eosinophilic granulomatosis with polyangiitis (EGPA; formerly known as Churg-Strauss syndrome).

Although a clear understanding of the various skin lesions in IgG4-related disease is a work in progress, skin lesions have been classified into subtypes based on documented cases:

- Angiolymphoid hyperplasia with eosinophilia (or lesions that mimic it) and cutaneous pseudolymphoma

- Cutaneous plasmacytosis

- Eyelid swelling (as part of Mikulicz's disease)

- Psoriasis-like eruptions

- Unspecified maculopapular or erythematous eruptions

- Hypergammaglobulinemic purpura and urticarial vasculitis

- Impaired blood supply to fingers or toes, leading to Raynaud's phenomenon or gangrene

Note:

In addition, Wells syndrome has also been reported in a case of IgG4-related disease.

Primary cutaneous amyloidosis is a form of amyloidosis associated with oncostatin M receptor. This type of amyloidosis has been divided into the following types:

- Macular amyloidosis is a cutaneous condition characterized by itchy, brown, rippled macules usually located on the interscapular region of the back. Combined cases of lichen and macular amyloidosis are termed biphasic amyloidosis, and provide support to the theory that these two variants of amyloidosis exist on the same disease spectrum.

- Lichen amyloidosis is a cutaneous condition characterized by the appearance of occasionally itchy lichenoid papules, typically appearing bilaterally on the shins.

- Nodular amyloidosis is a rare cutaneous condition characterized by nodules that involve the acral areas.

IgG4-related skin disease is the recommended name for skin manifestations in IgG4-related disease (IgG4-RD). Multiple different skin manifestations have been described.

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.

Acute cutaneous lupus erythematosus is a cutaneous condition characterized by a bilateral malar rash (also known as a "butterfly rash") and lesions that tend to be transient, and that follow sun exposure.

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.

Symptoms vary from person to person, and may come and go. Almost everyone with lupus has joint pain and swelling. Some develop arthritis. Frequently affected joints are the fingers, hands, wrists, and knees.

Other common symptoms include:

- chest pain during respiration

- joint pain

- oral ulcer

- fatigue

- fever with no other cause

- general discomfort, uneasiness, or ill feeling (malaise)

- hair loss

- sensitivity to sunlight

- skin rash – a "butterfly" rash in about half people with SLE

- swollen lymph nodes

Although lichen planus can present with a variety of lesions, the most common presentation is as a well defined area of purple-coloured, itchy, flat-topped papules with interspersed lacy white lines (Wickham's striae). This description is known as the characteristic "6 Ps" of lichen planus: planar (flat-topped), purple, polygonal, pruritic, papules, and plaques. This rash, after regressing, is likely to leave an area of hyperpigmentation that slowly fades. That said, a variety of other lesions can also occur.

Jessner lymphocytic infiltrate of the skin is a cutaneous condition characterized by a persistent papular and plaque-like skin eruption which can occur on the neck, face and back and may re-occur. This is an uncommon skin disease and is a benign collection of lymph cells. Its cause is not known and can be hereditary. It is named for Max Jessner. It is thought to be equivalent to lupus erythematosus tumidus.

It can occur as the result of ACE inhibitors and a number of medications used to treat multiple sclerosis including glatiramer acetate.

Cutaneous lymphoid hyperplasia refers to a groups of benign cutaneous disorders characterized by collections of lymphocytes, macrophages, and dendritic cells in the skin. Conditions included in this groups are:

- Cutaneous lymphoid hyperplasia with nodular pattern, a condition of the skin characterized by a solitary or localized cluster of asymptomatic erythematous to violaceous papules or nodules

- Cutaneous lymphoid hyperplasia with bandlike and perivascular patterns, a condition of the skin characterized by skin lesions that clinically resemble mycosis fungoides

Non-mycosis fungoides CD30− cutaneous large T-cell lymphoma is a cutaneous condition that usually presents as solitary or generalized plaques, nodules, or tumors of short duration.

A cutaneous condition is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment.

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying causes and pathogenetics are often not known. Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), cause (skin conditions resulting from physical factors), and so on.

Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow). The diagnosis of many conditions often also requires a skin biopsy which yields histologic information that can be correlated with the clinical presentation and any laboratory data. The introduction of cutaneous ultrasound has allowed the detection of cutaneous tumors, inflammatory processes, nail disorders and hair diseases.

The disease usually affects the lower legs or scrotum. The swelling is accompanied by rough nodules or wart-like plaques on the skin. If the disease is not treated, it eventually results in pain and immobility.

Occasionally, lichen planus is known to occur with other conditions. For example:

- Lupus erythematosus overlap syndrome. Lesions of this syndrome share features of both lupus erythematosus and lichen planus. Lesions are usually large and hypopigmented, atrophic, and with a red to blue colour and minimal scaling. Telangectasia may be present.

- Lichen sclerosus overlap syndrome, sharing features of lichen planus and lichen sclerosus.

Lupus erythematosus is a name given to a collection of autoimmune diseases in which the human immune system becomes hyperactive and attacks healthy tissues. Symptoms of these diseases can affect many different body systems, including joints, skin, kidneys, blood cells, heart, and lungs. The most common and severe form is systemic lupus erythematosus.

Retiform parapsoriasis is a cutaneous condition, considered to be a type of large-plaque parapsoriasis. It is characterized by widespread, ill-defined plaques on the skin, that have a net-like or zebra-striped pattern. Skin , a wasting away of the cutaneous tissue, usually occurs within the area of these plaques.

Although elephantiasis nostras resembles the elephantiasis caused by helminths, it is not a filarial disease. Instead, it is a complication of chronic lymphedema. Both elephantiasis nostras and filarial elephantiasis are characterized by impaired lymphatic drainage, which results in excess fluid accumulation.

Because the TVC's entry point usually is the site of a trauma, wound or puncture in the skin (during an autopsy, for example), the most frequent site for the wart are the hands. But it can occur anywhere in the skin, such as in the sole of the feet, in the anus, and, in the case of children from developing countries, in the buttocks and knees. This is because children from countries of high incidence of tuberculosis can contract the lesion after contact with tuberculous sputum, by walking barefoot, sitting or playing on the ground.

When recent, the skin lesion has the outside appearance of a wart or verruca, thus it can be confused with other kinds of warts. It evolves to an annular red-brown plaque with time, with central healing and gradual expansion in the periphery. In this phase, it can be confused with fungal infections such as blastomycosis and chromoblastomycosis.

Erythroderma is generalized exfoliative dermatitis, which involves 90% or more of the patient's skin. The most common cause of erythroderma is exacerbation of an underlying skin disease, such as psoriasis, contact dermatitis, seborrheic dermatitis, lichen planus, pityriasis rubra pilaris or a drug reaction. Primary erythroderma is less frequent and is usually seen in cases of cutaneous T-cell lymphoma, in particular in Sézary's disease.

The most common causes of exfoliative dermatitis are best remembered by the mnemonic device ID-SCALP. The causes and their frequencies are as follows:

- Idiopathic - 30%

- Drug allergy - 28%

- Lymphoma and leukemia - 14%

- Atopic dermatitis - 10%

- Psoriasis - 8%

- Contact dermatitis - 3%

- Seborrheic dermatitis - 2%

Differential diagnosis in patients with erythroderma may be difficult.