The formation of gummata is rare in developed countries, but common in areas that lack adequate medical treatment.

Syphilitic gummas are found in most but not all cases of tertiary syphilis, and can occur either singly or in groups. Gummatous lesions are usually associated with long-term syphilitic infection; however, such lesions can also be a symptom of benign late syphilis.

A trumpeter's wart is a cutaneous condition characterized by a firm, fibrous, hyperkeratotic nodule on the upper lip of a trumpet player.

Syringofibroadenoma (also known as "acrosyringeal nevus of Weedon and Lewis") is a cutaneous condition characterized by a hyperkeratotic nodule or plaque involving the extremities.

It is considered of eccrine origin.

A sebaceous adenoma, a type of adenoma, a cutaneous condition characterized by a slow-growing tumor usually presenting as a pink, flesh-coloured, or yellow papule or nodule.

Colloid nodules, also known as adenomatous nodules or colloid nodular goiter are benign, noncancerous enlargement of thyroid tissue. Although they may grow large, and there may be more than one, they are not malignant and they will not spread beyond the thyroid gland. Colloid nodules are the most common kind of thyroid nodule.

Papillary eccrine adenoma (also known as "tubular apocrine adenoma") is a cutaneous condition characterized by an uncommon benign sweat gland neoplasm that presents as a dermal nodule located primarily on the extremities of black patients.

Microcystic adnexal carcinoma (also known as sclerosing sweat duct carcinoma) is a cutaneous condition characterized by a slow-growing plaque or nodule.

Eccrine carcinoma (also known as a syringoid carcinoma) is a rare cutaneous condition characterized by a plaque or nodule on the scalp, trunk, or extremities.

Angiolymphoid hyperplasia with eosinophilia (also known as: "Epithelioid hemangioma," "Histiocytoid hemangioma," "Inflammatory angiomatous nodule," "Intravenous atypical vascular proliferation," "Papular angioplasia," "Inflammatory arteriovenous hemangioma," and "Pseudopyogenic granuloma") usually presents with pink to red-brown, dome-shaped, dermal papules or nodules of the head or neck, especially about the ears and on the scalp.

It, or a similar lesion, has been suggested as a feature of IgG4-related skin disease, which is the name used for skin manifestations of IgG4-related disease.

Milker's nodules (or "milkmaid blisters") are a cutaneous condition that is most commonly transmitted from the udders of infected cows. Milker's nodule is caused by Paravaccinia virus. Disease in humans is nearly identical to Orf.

Spiradenoma, also spiroma or eccrine spiradenoma, is a cutaneous condition that is typically characterized, clinically, as a solitary, deep-seated dermal nodule of approximately one centimeter, occurring on the ventral surface of the body. Spiradenoma lesions are benign sudoriferous tumors, and have also been described as cystic epitheliomas of the sweat glands.

The histological origin is controversial.

The histological and ultrastructural features of Ledderhose and Dupuytren's disease are the same, which supports the hypothesis that they have a common cause and pathogenesis. As with Dupuytren's disease, the root cause(s) of Ledderhose's disease are not yet understood. It has been noted that it is an inherited disease and of variable occurrence within families, i.e. the genes necessary for it may remain dormant for a generation or more and then surface in an individual, or be present in multiple individuals in the same generation with varying degree.

There are certain identified risk factors. The disease is more commonly associated with -

- A family history of the disease

- Higher incidence in males

- Palmar fibromatosis 10-65% of the time.

- Peyronie's disease

- Epilepsy patients

- Patients of diabetes mellitus

There is also a suspected, although unproven, link between incidence and alcoholism, smoking, liver diseases, thyroid problems, and stressful work involving the feet.

In syphilis, the gumma is caused by reaction to spirochaete bacteria in the tissue.

It appears to be the human body's way to slow down the action of this bacteria, it is a unique immune response that develops in humans after the immune system fails to kill off syphilis.

Idiopathic facial aseptic granuloma is a cutaneous condition characterized by a chronic, painless, solitary nodule, reminiscent of an acne nodule, appearing on the cheeks of young children. It has a prolonged course, but spontaneously heals.

Cutaneous focal mucinosis is a skin condition characterized by a solitary nodule or papule.

Solitary cutaneous leiomyoma typically presents as a deeply circumscribed, freely movable, rounded nodule ranging from 2 to 15mm in diameter, with overlying skin that may have a reddish or violaceous tint.

A limbal nodule is any nodular lesion at the limbus (junction of the cornea and sclera) of the eye.

The differential diagnosis for a limbal nodule can include:

- Pinguecula

- Early Pterygium

- Foreign body / foreign body granuloma

- Phlycten, an inflamed nodule of lymphoid tissue

- Episcleritis

- Scleritis

- Granuloma

- Limbal dermoid, a kind of choristoma (NB: in other organs "dermoid" can refer to a teratoma)

- malignant melanoma

Warty dyskeratoma, also known as an Isolated dyskeratosis follicularis, is a benign epidermal proliferation with distinctive histologic findings that may mimic invasive squamous cell carcinoma and commonly manifests as an umbilicated (Having a central mark or depression resembling a navel) lesion with a keratotic plug, WD have some histopathologic similarities to viral warts but it's not caused by HPV and the majority of these lesions display overall histopathologic features consistent with a follicular adnexal neoplasm. usually limited to the head, neck, scalp or face and vulva. Lesions are generally and sporadic and may be associated with a follicular unit. Oral involvement, particularly the hard palate, and genital involvement have been reported. it can also be thought of as one of the manifestations of focal acantholytic dyskeratosis, an epidermal reaction pattern that can be seen in several disorders, including Darier's disease and Grover's disease. But the main Difference between Darier disease and Warty dyskeratoma, is that Darier disease inherited dermatosis (autosomal dominant) consisting of multiple keratotic papules on the face, trunk, and extremities, while WD occurs as an isolated, noninherited, single keratotic nodule mainly confined to the head and neck as mentioned earlier.

A papillary hidradenoma, also hidradenoma papilliferum, is a sharply circumscribed nodule or benign tumor of the apocrine gland usually found on the labia majora or the interlabial folds. It is benign tissue (not cancerous) but is often confused clinically with carcinoma of the vulva because of its tendency to ulcerate.

Fibroma of tendon sheath is a benign tumor that presents as a small subcutaneous nodule that slowly increases in size. The tumors often have a multinodular growth pattern, with individual nodules being composed of bland, slender, spindle-shaped cells (myofibroblasts) in a dense, fibrous matrix.” A common microscopic finding is the presence of elongated, slit-like blood vessels. The lesions nearly always arise in the distal portions of the extremities. They often occur on the fingers, hands, toes, or feet. Although they are benign, they may recur in up to 40% of cases.

Although they may be regarded as a tumor of the skin, the lesions arise from tendons and aponeuroses in superficial sites, and are therefore properly classified as in the category "soft tissue tumor."

The biological nature of Fibroma of tendon sheath is not known, but the category appears to comprise a number of different pathologic processes. It is considered that about one-third of the lesions in this category may be acral variants of the entity, nodular fasciitis.

The condition is usually seen in otherwise healthy people. Occasionally, it may be associated with diabetes or thyroid disease. It has also been associated with auto-immune diseases such as systemic lupus erythematosus, rheumatoid arthritis, Lyme disease and Addison's disease. At this time no conclusive connection has been made between patients.

Warty dyskeratoma must be differentiated from vulvar dysplasia, Bowenoid papulosis, squamous carcinoma, condyloma, and other viral-induced squamous lesions.

Clear cell acanthoma (also known as "Acanthome cellules claires of Degos and Civatte," "Degos acanthoma," and "Pale cell acanthoma") is a benign clinical and histological lesion initially described as neoplastic, which some authors now regard as a reactive dermatosis. It usually presents as a moist solitary firm, brown-red, well-circumscribed, 5 mm to 2 cm nodule or plaque on the lower extremities of middle-aged to elderly individuals The lesion has a crusted, scaly peripheral collarette and vascular puncta on the surface. It is characterized by slow growth, and may persist for years. The clinical differential diagnosis includes: dermatofibroma, inflamed seborrheic keratosis, pyogenic granuloma, basal cell carcinoma, squamous cell carcinoma, verruca vulgaris, psoriatic plaque, and melanoma.

EN is associated with a wide variety of conditions, including:

- Idiopathic

In about 30–50% of cases, the cause of EN is unknown.

- Infection

- Streptococcal infection which, in children, is by far the most common precipitant,

- Primary infection of Tuberculosis

- "Mycoplasma pneumoniae"

- "Histoplasma capsulatum"

- "Yersinia"

- Epstein-Barr virus

- "Coccidioides immitis" (Valley fever)

- Cat scratch disease

- Autoimmune disorders, including

- Inflammatory bowel disease (IBD)

- Behçet's disease

- Sarcoidosis

- Pregnancy

- Medications, including

- Sulfonamides

- Penicillins

- Oral contraceptives

- Bromides

- Hepatitis B vaccination

- Cancer, including

- Non-Hodgkins lymphoma (NHL)

- Carcinoid tumours

- Pancreatic cancer

EN may also be due to excessive antibody production in lepromatous leprosy leading to deposition of immune complexes.

There is an association with the HLA-B27 histocompatibility antigen, which is present in 65% of patients with erythema nodosum.

A useful mnemonic for causes is SORE SHINS (Streptococci, OCP, Rickettsia, Eponymous (Behçet), Sulfonamides, Hansen's Disease (Leprosy), IBD, NHL, Sarcoidosis.

Melanoma with features of a Spitz nevus (also known as a "Spitzoid melanoma") is a cutaneous condition characterized histologically with tissue similar to a spitz nevus and with overall symmetry and a dermal nodule of epithelioid melanocytes that do not mature with progressively deeper dermal extension.