Clinical diagnosis can be made with the naked eye using the ABCD guideline or by using dermatoscopy. An online-screening test is also available to help screen out benign moles.

It often requires a dermatologist to fully evaluate moles. For instance, a small blue or bluish-black spot, often called a blue nevus, is usually benign but often mistaken for melanoma. Conversely, a junctional nevus, which develops at the junction of the dermis and epidermis, is potentially cancerous.

A basic reference chart used for consumers to spot suspicious moles is found in the mnemonic A-B-C-D, used by institutions such as the American Academy of Dermatology and the National Cancer Institute. The letters stand for asymmetry, border, color, and diameter. Sometimes, the letter E (for elevation or evolving) is added. According to the American Academy of Dermatology, if a mole starts changing in size, color, shape or, especially, if the border of a mole develops ragged edges or becomes larger than a pencil eraser, it would be an appropriate time to consult with a physician. Other warning signs include a mole, even if smaller than a pencil eraser, that is different from the others and begins to crust over, bleed, itch, or become inflamed. The changes may indicate developing melanomas. The matter can become clinically complicated because mole removal depends on which types of cancer, if any, come into suspicion.

A recent and novel method of melanoma detection is the "ugly duckling sign" It is simple, easy to teach, and highly effective in detecting melanoma. Simply, correlation of common characteristics of a person's skin lesion is made. Lesions which greatly deviate from the common characteristics are labeled as an "ugly duckling", and further professional exam is required. The "little red riding hood sign", suggests that individuals with fair skin and light colored hair might have difficult-to-diagnose melanomas. Extra care and caution should be rendered when examining such individuals as they might have multiple melanomas and severely dysplastic nevi. A dermatoscope must be used to detect "ugly ducklings", as many melanomas in these individuals resemble non-melanomas or are considered to be "wolves in sheep clothing". These fair skinned individuals often have lightly pigmented or amelanotic melanomas which will not present easy-to-observe color changes and variation in colors. The borders of these amelanotic melanomas are often indistinct, making visual identification without a dermatoscope very difficult.

People with a personal or family history of skin cancer or of dysplastic nevus syndrome (multiple atypical moles) should see a dermatologist at least once a year to be sure they are not developing melanoma.

Nevi are typically diagnosed clinically with the naked eye or using dermatoscopy. More advanced imaging tests are available for distinguishing melanocytic nevi from melanoma, including computerized dermoscopy and image analysis. The management of nevi depends on the type of nevus and the degree of diagnostic uncertainty. Some nevi are known to be benign, and may simply be monitored over time. Others may warrant more thorough examination and biopsy for histopathological examination (looking at a sample of skin under a microscope to detect unique cellular features). For example, a clinician may want to determine whether a pigmented nevus is a type of melanocytic nevus, dysplastic nevus, or melanoma as some of these skin lesions pose a risk for malignancy. The ABCDE criteria (asymmetry, border irregularity, color variegation, diameter > 6 mm, and evolution) are often used to distinguish nevi from melanomas in adults, while modified criteria (amelanosis, bleeding or bumps, uniform color, small diameter or de novo, and evolution) can be used when evaluating suspicious lesions in children. In addition to histopathological examination, some lesions may also warrant additional tests to aid in diagnosis, including special stains, immunohistochemistry, and electron microscopy. Typically; the nevi which exist since childhood are harmless

The management of a nevus depends on the specific diagnosis, however, the options for treatment generally include the following modalities:

Large and especially giant congenital nevi are at higher risk for malignancy degeneration into melanoma. Because of the premalignant potential, it is an acceptable clinical practice to remove congenital nevi electively in all patients and relieve the nevocytic overload.

First dilemma in diagnosis is recognition. As lentigo malignas often present on severely sun-damaged skin, it is frequently found amongst numerous pigmented lesions – thin seborrheic keratoses, lentigo senilis, lentigines. It is difficult to distinguish these lesions with the naked eye alone, and even with some difficulty using dermatoscopy. As the lentigo maligna is often very large, it often merges with, or encompasses other skin tumors – such as lentigines, melanocytic nevi, and seborrheic keratosis.

Second dilemma is the biopsy technique. Even though excisional biopsy (removing the entire lesion) is ideal, and advocated by pathologists; practical reason dictates that this should not be done. These tumors are often large and presenting on the facial area. Excision of such large tumor would be absolutely contraindicated if the lesion's identity is uncertain. The preferred method of diagnosis is by using a punch biopsy, allowing the physician to sample multiple full thickness pieces of the tumor at multiple sites. While one section of the tumor might show benign melanocytic nevus, another section might show features concerning for severe cellular atypia. When cellular atypia is noted, a pathologist might indicate that the entire lesion should be removed. It is at this point that one can comfortablly remove the entire lesion, and thus confirm the final diagnosis of lentigo maligna. The size of the punch biopsy can vary from 1 mm to 2 mm, but it is preferable to use a punch 1.5 mm or larger. Representative samples of the most atypical parts of the nevus should be biopsied, often guided by dermatoscopy.

Benign congenital nevi can have histological characteristics resembling melanomas, often breaking most if not all of the ABCDE rules. Dermatoscopic findings of the smaller forms of benign congenital nevi can aid in their differentiation from other pigmented neoplasms.

Microscopically, congenital melanocytic nevi appear similar to acquired nevi with two notable exceptions. For the congenital nevus, the neval cells are found deeper into the dermis. Also, the deeper nevus cells can be found along with neurovascular bundles, with both surrounding hair follicles, sebaceous glands, and subcutaneous fat. Such annexes and the hypodermis can also be hypoplasic or, conversely, present aspects of hamartoma.

Treatment is by excisional biopsy, wide local excision and possibly sentinel node biopsy. Spread of disease to local lymph nodes or distant sites (typically brain, bone, skin and lung) marks a decidedly poor prognosis.

First dilemma in diagnosis is recognition. As lentigo malignas often present on severely sun damaged skin, it is frequently found amongst numerous pigmented lesions - thin seborrheic keratoses, lentigo senilis, lentigines. It is difficult to distinguish these lesions with the naked eye alone, and even with some difficulty using dermatoscopy. As the lentigo maligna is often very large, it often merges with, or encompasses other skin tumors - such as lentigines, melanocytic nevi, and seborrheic keratosis.

Second dilemma is the biopsy technique. Even though excisional biopsy (removing the entire lesion) is ideal, and advocated by pathologists, practical reason dictates that this should not be done. These tumors are often large and presenting on the facial area. Excision of such large tumor would be absolutely contraindicated if the lesion's identity is uncertain. The preferred method of diagnosis is by using a shave biopsy because punch biopsies give up to an 80% false negative rate. While one section of the tumor might show benign melanocytic nevus, another section might show features concerning of severe cellular atypia. When cellular atypia is noted, a pathologist might indicate that the entire lesion should be removed. It is at this point that one can comfortably remove the entire lesion, thus confirming the final diagnosis of lentigo maligna. Despite the high false negative rate, punch biopsies are often used and the size of the punch biopsy can vary from 1 mm to 2 mm, but it is preferred to use a punch 1.5 mm or larger. Representative samples of the most atypical part of the nevus should be biopsy, often by the aid of dermatoscopy.

Also known as "scoop", "scallop", or "shave" excisional biopsy, or "shave excision". A trend has occurred in dermatology over the last 10 years with the advocacy of a deep shave excision of a pigmented lesion An author published the result of this method and advocated it as better than standard excision and less time consuming. The added economic benefit is that many surgeons bill the procedure as an excision, rather than a shave biopsy. This save the added time for hemostasis, instruments, and suture cost. The great disadvantage, seen years later is the numerous scallop scars, and a very difficult to deal with lesions called a "recurrent melanocytic nevus". What has happened is that many "shave" excisions does not adequately penetrate the dermis or subcutanous fat enough to include the entire melanocytic lesion. Residual melanocytes regrow into the scar. The combination of scarring, inflammation, blood vessels, and atypical pigmented streaks seen in these recurrent nevus gives the perfect dermatoscopic picture of a melanoma. When a second physicians re-examine the patient, he or she has no choice but to recommend the reexcision of the scar. If one does not have access to the original pathology report, it is impossible to tell a recurring nevus from a severely dysplastic nevus or a melanoma. As the procedure is widely practiced, it is not unusual to see a patient with dozens of scallop scars, with as many as 20% of the scars showing residual pigmentation. The second issue with the shave excision is fat herniation, iatrogenic anetoderma, and hypertrophic scarring. As the deep shave excision either completely remove the full thickness of the dermis or greatly diminishing the dermal thickness, subcutanous fat can herniate outward or pucker the skin out in an unattractive way. In areas prone to friction, this can result in pain, itching, or hypertrophic scarring.

Treatment depends on the thickness of the invasive component of the lentigo maligna. Treatment is essentially identical to other melanomas of the same thickness and stage.

The best treatment of lentigo maligna is not clear as it has not been well studied.

Standard excision is still being done by most surgeons. Unfortunately, the recurrence rate is high (up to 50%). This is due to the ill defined visible surgical margin, and the facial location of the lesions (often forcing the surgeon to use a narrow surgical margin). The use of dermatoscopy can significantly improve the surgeon's ability to identify the surgical margin. The narrow surgical margin used (smaller than the standard of care of 5 mm), combined with the limitation of the standard bread loafing technique of fixed tissue histology - result in a high "false negative" error rate, and frequent recurrences. Margin controlled (peripheral margins) is necessary to eliminate the false negative errors. If breadloafing is utilized, distances from sections should approach 0.1 mm to assure that the method approaches complete margin control.

Where the lesion is on the face and either large or 5mm margins are possible, a skin flap or skin graft may be indicated/required. Grafts have their own risks of failure and poor cosmetic outcomes. Flaps can require extensive incision resulting in long scars and may be better done by plastic surgeons (and possibly better again by those with extensive LM or "suspicious of early malignant melanoma" experience.

Mohs surgery has been done with cure rate reported to be 77%. The "double scalpel" peripheral margin controlled excision method approximates the Mohs method in margin control, but requires a pathologist intimately familiar with the complexity of managing the vertical margin on the thin peripheral sections and staining methods.

Some melanocytic nevi, and melanoma-in-situ (lentigo maligna) have resolved with an experimental treatment, imiquimod (Aldara) topical cream, an immune enhancing agent. In view of the very poor cure rate with standard excision, some surgeons combine the two methods: surgical excision of the lesion, then three months treatment of the area with imiquimod cream.

Studies seem to conflict about the level of certainty associated with using imiquimod.

Another treatment to be considered where standard margins cannot be achieved or cosmetics are a major consideration is ultra-soft x-ray/grenz-ray radiation.

In the very elderly or those with otherwise limited life expectancy, the impact of major day surgery for excision with 5mm margins and large skin flap could be worse than doing nothing or the possibility of failed treatments with imiquimod or Grenz ray.

Screening for melanoma in FAMMM kindreds should begin at age 10 with a baseline total body skin examination including scalp, eyes, oral mucosa, genital area, and nail, as family members may develop melanoma in their early teens.

At Mayo Clinic, FAMMM patients with a confirmed mutation and family history of pancreatic cancer are offered screening with either high-resolution pancreatic protocol CT, MRI, or endoscopic ultrasound starting at age 50 or 10 years younger than the earliest family member with pancreas cancer. They are counseled on the lack of evidence-based data to support screening, and on the limitations of our current technology to detect a lesion at a stage amenable to therapy.

Most birthmarks are harmless and do not require treatment. Pigmented marks can resolve on their own over time in some cases. Vascular birthmarks may require reduction or removal for cosmetic reasons. Treatments include administering oral or injected steroids, dermatological lasers to reduce size and/or color, or dermatologic surgery.

Usually observed at birth or shortly thereafter in 94% of patients, in other reports, patients did not develop skin lesions until 3 months or even 2 years after birth. Females are typically affected more often than males (64%).

If a patient displays congenital melanocytic nevi or giant congenital melanocytic nevi, the criteria for diagnosis of neurocutaneous melanosis is as follows:

- Melanocytic deposits exist within the central nervous system that are either malignant or benign

- The cutaneous lesions, giant or otherwise, are not malignant

This criteria is typically validated through biopsy of the cutaneous lesions and imaging of the central nervous system. It is important to establish that the cutaneous lesions are benign. If not, then the melanocytic deposits in the central nervous system may be the result of metastasis of cutaneous melanoma and not neurocutaneous melanosis.

Imaging has been shown to be the only reliable detection method for the presence of neurocutaneous melanosis that can be performed in living patients. Currently, the preferred imaging modality for diagnosis of neurocutaneous melanosis is Magnetic Resonance Imaging, although ultrasound is another viable option. The signal due melanin deposits in the leptomeninges typical of neurocutaneous melanosis can be easily detected in MRI scans of patients under four months old. In patients above this age, there is some suggestion that normal brain myelination may partially obscure these signals.

As most patients with neurocutaneous melanosis are asymptomatic, those who are diagnosed through MR imaging are not guarantied to develop symptoms. Those diagnosed who did not develop symptoms ranged from 10% to 68%. This wide range is most likely due to the large number of asymptomatic, undiagnosed patients with neurocutaneous melanosis.

Spitz nevi are uncommon. Their annual incidence was estimated in a coastal population of sub-tropical Queensland to be 1.4 cases per 100,000 people. For comparison, the annual incidence of melanoma in the same population, which is high by world standards is 25.4 cases per 100,000 people.

Although they are most commonly found on people in their first two decades of life, the age range for people with Spitz nevi is from 6 months to 71 years, with a mean age of 22 years and a median age of 19 years.

The majority of patients with neurocutaneous melanosis are asymptomatic and therefore have a good prognosis with few complications. Most are not diagnosed, so definitive data in not available. For symptomatic patients, the prognosis is far worse. In patients without the presence of melanoma, more than 50% die within 3 years of displaying symptoms. While those with malignancy have a mortality rate of 77% with most patients displaying symptoms before the age of 2.

The presence of a Dandy-Walker malformation along with neurocutaneous melanosis, as occurs in 10% of symptomatic patients, further deteriorates prognosis. The median survival time for these patients is 6.5 months after becoming symptomatic.

Following a visual examination and a dermatoscopic exam, or "in vivo" diagnostic tools such as a confocal microscope, the doctor may biopsy the suspicious mole. A skin biopsy performed under local anesthesia is often required to assist in making or confirming the diagnosis and in defining severity. Elliptical excisional biopsies may remove the tumor, followed by histological analysis and Breslow scoring. Incisional biopsies such as punch biopsies are usually contraindicated in suspected melanomas, because of the possibility of sampling error or local implantation causing misestimation of tumour thickness. However, fears that such biopsies may increase the risk of metastatic disease seem unfounded.

Total body photography, which involves photographic documentation of as much body surface as possible, is often used during follow-up for high-risk patients. The technique has been reported to enable early detection and provides a cost-effective approach (with any digital camera), but its efficacy has been questioned due to its inability to detect macroscopic changes. The diagnosis method should be used in conjunction with (and not as a replacement for) dermoscopic imaging, with a combination of both methods appearing to give extremely high rates of detection.

Some patients have a few or no histopathologic abnormalities. Histological examination of a biopsy may show an increase in the number and size of capillaries and veins (rarely lymphatics), dilated capillaries located in the deeper dermis, and hyperplasia and swollen endothelial cells with occasional dilated veins and venous lakes.

A recent and novel method is the "ugly duckling sign". It is simple, easy to teach, and highly effective. Correlation of common lesion characteristics is made. Lesions that greatly deviate from the common characteristics are labeled an "Ugly Duckling", and a further professional exam is required. The "Little Red Riding Hood" sign suggests that individuals with fair skin and light-colored hair might have difficult-to-diagnose amelanotic melanomas. Extra care is required when examining such individuals, as they might have multiple melanomas and severely dysplastic nevi. A dermatoscope must be used to detect "ugly ducklings", as many melanomas in these individuals resemble non-melanomas or are considered to be "wolves in sheep's clothing". These fair-skinned individuals often have lightly pigmented or amelanotic melanomas that do not present easy-to-observe color changes and variations. Their borders are often indistinct, complicating visual identification without a dermatoscope.

Amelanotic melanomas and melanomas arising in fair-skinned individuals are very difficult to detect, as they fail to show many of the characteristics in the ABCD rule, break the "Ugly Duckling" sign and are hard to distinguish from acne scarring, insect bites, dermatofibromas, or lentigines.

Pseudomelanoma (also known as a "recurrent melanocytic nevus", and "recurrent nevus") is a cutaneous condition in which melantic skin lesions clinically resemble a superficial spreading melanoma at the site of a recent shave removal of a melanocytic nevus.

Currently, there is no consensus regarding type or frequency of scans following diagnosis and treatment of the primary eye tumor. Of the 50% of patients who develop metastatic disease, more than 90% of patients will develop liver metastases. As such, the majority of surveillance techniques are focused on the liver. These include abdominal magnetic resonance imaging (MRI), abdominal ultrasound and liver function tests. The scientific community is currently working to develop guidelines, but until then, each patient must take into consideration their individual clinical situation and discuss appropriate surveillance with their doctors.

Some ophthalmologists have also found promise with the use of intravitreal avastin injections in patients suffering from radiation-induced retinopathy, a side effect of plaque brachytherapy treatment, as well as imaging surveillance with SD-OCT.

A lentigo () (plural lentigines, ) is a small pigmented spot on the skin with a clearly defined edge, surrounded by normal-appearing skin. It is a harmless (benign) hyperplasia of melanocytes which is linear in its spread. This means the hyperplasia of melanocytes is restricted to the cell layer directly above the basement membrane of the epidermis where melanocytes normally reside. This is in contrast to the "nests" of multi-layer melanocytes found in moles (melanocytic nevi). Because of this characteristic feature, the adjective "lentiginous" is used to describe other skin lesions that similarly proliferate linearly within the basal cell layer.

Lentigines are distinguished from freckles (ephelis) based on the proliferation of melanocytes. Freckles have a relatively normal number of melanocytes but an increased "amount" of melanin. A lentigo has an increased "number" of melanocytes. Freckles will increase in number and darkness with sunlight exposure, whereas lentigines will stay stable in their color regardless of sunlight exposure.

Lentigines by themselves are benign, however one might desire the removal or treatment of some of them for cosmetic purposes. In this case they can be removed surgically, or lightened with the use of topical depigmentation agents. Some common depigmentation agents such as azelaic acid and kojic acid seem to be inefficient in this case, however other agents might work well (4% hydroquinone, 5% topical cysteamine, 10% topical ascorbic acid).

Conditions characterized by lentigines include:

- Lentigo simplex

- Solar lentigo (Liver spots)

- PUVA lentigines

- Ink spot lentigo

- LEOPARD syndrome

- Mucosal lentigines

- Multiple lentigines syndrome

- Moynahan syndrome

- Generalized lentiginosis

- Centrofacial lentiginosis

- Carney complex

- Inherited patterned lentiginosis in black persons

- Partial unilateral lentiginosis

- Peutz-Jeghers syndrome

- Lentigo maligna

- Lentigo maligna melanoma

- Acral lentiginous melanoma

Blue nevus (also known as "blue neuronevus", "dermal melanocytoma", and "nevus bleu") is a type of melanocytic nevus. The blue colour is caused by the pigment being deeper in the skin than in ordinary nevi. In principle they are harmless but they can sometimes be mimicked by malignant lesions, i.e. some melanomas can look like a blue nevus.