In longstanding scarred lesions, squamous cell carcinoma can develop.

On diascopy, it shows characteristic "apple-jelly" color. Biopsy will reveal tuberculoid granuloma with few bacilli. Mantoux test is positive.

The diagnosis is confirmed by a skin biopsy and a positive culture for acid-fast bacilli. A PPD test may also result positive.

For the diagnosis of lupus 4 out of 11 signs must be present.

Testing may include:

- Antinuclear antibody (ANA)

- CBC with differential

- Chest x-ray

- Serum creatinine

- Urinalysis

There is no official diagnostic criteria for UCTD. Diagnostic testing generally aims to determine whether a patient has a "definite" or "undifferentiated" connective tissue disease.

Antinuclear antibody (ANA) testing and anti-extractable nuclear antigen (anti-ENA) form the mainstay of serologic testing for SLE. Several techniques are used to detect ANAs. Clinically the most widely used method is indirect immunofluorescence (IF). The pattern of fluorescence suggests the type of antibody present in the people's serum. Direct immunofluorescence can detect deposits of immunoglobulins and complement proteins in the people's skin. When skin not exposed to the sun is tested, a positive direct IF (the so-called lupus band test) is an evidence of systemic lupus erythematosus.

ANA screening yields positive results in many connective tissue disorders and other autoimmune diseases, and may occur in normal individuals. Subtypes of antinuclear antibodies include anti-Smith and anti-double stranded DNA (dsDNA) antibodies (which are linked to SLE) and anti-histone antibodies (which are linked to drug-induced lupus). Anti-dsDNA antibodies are highly specific for SLE; they are present in 70% of cases, whereas they appear in only 0.5% of people without SLE. The anti-dsDNA antibody titers also tend to reflect disease activity, although not in all cases. Other ANA that may occur in people with SLE are anti-U1 RNP (which also appears in systemic sclerosis and mixed connective tissue disease), SS-A (or anti-Ro) and SS-B (or anti-La; both of which are more common in Sjögren's syndrome). SS-A and SS-B confer a specific risk for heart conduction block in neonatal lupus.

Other tests routinely performed in suspected SLE are complement system levels (low levels suggest consumption by the immune system), electrolytes and kidney function (disturbed if the kidney is involved), liver enzymes, and complete blood count.

The lupus erythematosus (LE) cell test was commonly used for diagnosis, but it is no longer used because the LE cells are only found in 50–75% of SLE cases, and they are also found in some people with rheumatoid arthritis, scleroderma, and drug sensitivities. Because of this, the LE cell test is now performed only rarely and is mostly of historical significance.

Most patients will maintain a diagnosis of undifferentiated connective tissue disease. However, about one third of UCTD patients will differentiate to a specific autoimmune disease, like rheumatoid arthritis or systemic sclerosis. About 12 percent of patients will go into remission.

Severe vitamin D deficiency has been associated with the progression of UCTD into defined connective tissue diseases. The presence of the autoantibodies anti-dsDNA, anti-Sm, and anti-cardiolipin has been shown to correlate with the development of systemic lupus erythematosus, specifically.

Some physicians make a diagnosis on the basis of the American College of Rheumatology (ACR) classification criteria. The criteria, however, were established mainly for use in scientific research including use in randomized controlled trials which require higher confidence levels, so many people with SLE may not pass the full criteria.

Lupus erythematosus may manifest as systemic disease or in a purely cutaneous form also known as "incomplete lupus erythematosus". Lupus has four main types:

- systemic

- discoid

- drug-induced

- neonatal

Of these, systemic lupus erythematosus (also known as SLE) is the most common and serious form.

A more thorough categorization of lupus includes the following types:

- acute cutaneous lupus erythematosus

- subacute cutaneous lupus erythematosus

- discoid lupus erythematosus (chronic cutaneous)

- childhood discoid lupus erythematosus

- generalized discoid lupus erythematosus

- localized discoid lupus erythematosus

- chilblain lupus erythematosus (Hutchinson)

- lupus erythematosus-lichen planus overlap syndrome

- lupus erythematosus panniculitis (lupus erythematosus profundus)

- tumid lupus erythematosus

- verrucous lupus erythematosus (hypertrophic lupus erythematosus)

- cutaneous lupus mucinosis

- complement deficiency syndromes

- drug-induced lupus erythematosus

- neonatal lupus erythematosus

- systemic lupus erythematosus

Subacute cutaneous lupus erythematosus (SCLE) is a clinically distinct subset of cases of lupus erythematosus that is most often present in white women aged 15 to 40, consisting of skin lesions that are scaly and evolve as polycyclic annular lesions or plaques similar to those of plaque psoriasis.

Characteristically the lesions appear in sun-exposed areas such as the vee of the neckline or the forearms, but not the face. It may be brought on by sun-sensitizing medications, but is usually associated with autoimmune disorders such as rheumatoid arthritis and Sjögren's syndrome.

Treatment generally involves sun avoidance and protection and topical corticosteroids. Sometimes systemic drug treatment is necessary. Besides corticosteroids other immunosuppressants such as methotrexate are also used.

Lesions of SCLE may have an annular configuration, with raised red borders and central clearing.

Therapy for cutaneous tuberculosis is the same as for systemic tuberculosis, and usually consists of a 4-drug regimen, i.e., isoniazid, rifampin, pyrazinamide, and ethambutol or streptomycin.

Tumid lupus erythematosus (also known as "lupus erythematosus tumidus") is a rare, but distinctive entity in which patients present with edematous erythematous plaques, usually on the trunk.

Lupus erythematosus tumidus (LET) was reported by Henri Gougerot and Burnier R. in 1930. It is a photosensitive skin disorder, a different subtype of cutaneous lupus erythematosus (CLE) from discoid lupus erythematosus (DLE) or subacute CLE (SCLE). LET is usually found on sun-exposed areas of the body. Skin lesions are edematous, urticarialike annular papules and plaques. Topical corticosteroids are not effective as treatment for LET, but many will respond to chloroquine. LET resolves with normal skin, no residual scarring, no hyperpigmentation or hypopigmentation. Cigarette smokers who have LET may not respond very well to chloroquine.

It has been suggested that it is equivalent to Jessner lymphocytic infiltrate of the skin.

Antinuclear antibodies are usually positive in drug induced Lupus. Anti-Neutrophil Cytoplasmic antibodies (ANCA) can also be positive in association with certain drugs. Furthermore, Anti-Histone antibodies can also be positive in drug induced lupus.

Anti-Histone antibodies are positive in up to 95% of patients with drug induced lupus. DIThe most common medications associated with drug induced lupus are hydralazine, procainamide, isoniazid, methyldopa, chlorpromazine, quinidine, and minocycline.

Discoid lupus erythematosus (DLE) is a chronic skin condition of sores with inflammation and scarring favouring the face, ears, and scalp and at times on other body areas. These lesions develop as a red, inflamed patch with a scaling and crusty appearance. The centre areas may appear lighter in colour with a rim darker than the normal skin.

Discoid lupus erythematosus can be divided into localised, generalised, and childhood discoid lupus erythematosus.

Verrucous lupus erythematosus (also known as "Hypertrophic lupus erythematosus") presents with non-pruritic papulonodular lesions on the arms and hands, resembling keratoacanthoma or hypertropic lichen planus.

Chilblain lupus erythematosus (also known as "chilblain lupus erythematosus of Hutchinson") is a chronic, unremitting form of lupus erythematosus with the fingertips, rims of ears, calves, and heels affected, especially in women.

Localised discoid lupus erythematosus typically presents with skin lesions localised above the neck, with favoured sites being the scalp, bridge of the nose, cheeks, above the lips and ears as well as the arms hair scratching glasses touching name="Andrews1"/> Another form of discoid lupus erythematosus includes oral discoid. Oral discoid lupus erythematosus results in oral lesions which present themselves as white spots, ulcers and central erythema lesions. Oral discoid lesions most commonly occur on the labial mucosa, vermillion border and buccal mucosa. Atrophy may be observed in some cases. Dentists may be important in establishing the diagnosis before the cutaneous lesions become apparent.

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.

Lupus erythematosus panniculitis (also known as "Lupus erythematosus profundus", "Lupus panniculitis", "Lupus profundus", and "Subcutaneous lupus erythematosus") presents with subcutaneous nodules that are commonly firm, sharply defined and nontender.

Tufted folliculitis presents with doll's hair-like bundling of follicular units, and is seen in a wide range of scarring conditions including chronic staphylococcal infection, chronic lupus erythematosus, lichen planopilaris, Graham-Little syndrome, folliculitis decalvans, acne keloidalis nuchae, immunobullous disorders, and dissecting cellulitis.

Alpha-1 antitrypsin deficiency panniculitis is a panniculitis associated with a deficiency of the α-antitrypsin enzyme.

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.

Pemphigus erythematosus (also known as "Senear–Usher syndrome") is simply a localized form of pemphigus foliaceus with features of lupus erythematosus.

The differential diagnosis of Kikuchi disease includes systemic lupus erythematosus (SLE), disseminated tuberculosis, lymphoma, sarcoidosis, and viral lymphadenitis. Clinical findings sometimes may include positive results for IgM/IgG/IgA antibodies.

For other causes of lymph node enlargement, see lymphadenopathy.

The disease mimics many other dermatoses and can be confused with conditions, such as sarcoidosis, discoid lupus erythematosus, mycosis fungoides, and fixed drug eruption.