Melanonychia
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Melanonychia is a black or brown pigmentation of a nail, and may be present as a normal finding on many digits in Afro-Caribbeans, as a result of trauma, systemic disease, or medications, or as a postinflammatory event from such localized events as
lichen planus Lichen planus (LP) is a chronic inflammatory and autoimmune disease that affects the skin, nails, hair, and mucous membranes. It is not an actual lichen, but is named for its appearance. It is characterized by polygonal, flat-topped, violaceous p ...
or fixed drug eruption.James, William; Berger, Timothy; Elston, Dirk (2005). ''Andrews' Diseases of the Skin: Clinical Dermatology''. (10th ed.). Saunders. .Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. . There are two types, longitudinal and transverse melanonychia.


Signs and symptoms

Melanonychia is defined by a darkening of the nail plate that is brown to black; the pigment in question is typically
melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...
. It can affect one or more fingernails as well as toenails.


Causes

Melanocytic activation and melanocyte proliferation are the two primary processes of melanonychia. Increased
melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...
production from a typical number of activated
melanocyte Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the eye (the uvea), the inner ear, vagina ...
s in the nail matrix is referred to as melanocytotic activation. Increased
melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...
pigment results from a greater quantity of
melanocyte Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the eye (the uvea), the inner ear, vagina ...
s within the nail matrix, which is known as melanocyte proliferation. Both pregnancy and racial melanonychia are physiological causes of longitudinal melanonychia. People with dark skin tones, including
African Americans African Americans, also known as Black Americans and formerly also called Afro-Americans, are an American racial and ethnic group that consists of Americans who have total or partial ancestry from any of the Black racial groups of Africa ...
,
Asians "Asian people" (sometimes "Asiatic people")United States National Library of Medicine. Medical Subject Headings. 2004. November 17, 200Nlm.nih.gov: ''Asian Continental Ancestry Group'' is also used for categorical purposes. is an umbrella term ...
,
Hispanic The term Hispanic () are people, Spanish culture, cultures, or countries related to Spain, the Spanish language, or broadly. In some contexts, Hispanic and Latino Americans, especially within the United States, "Hispanic" is used as an Ethnici ...
s, and people from the
Middle East The Middle East (term originally coined in English language) is a geopolitical region encompassing the Arabian Peninsula, the Levant, Turkey, Egypt, Iran, and Iraq. The term came into widespread usage by the United Kingdom and western Eur ...
, often exhibit harmless longitudinal pigmented stripes. It is important to investigate the possibility of
onychotillomania Onychotillomania is a compulsive behavior in which a person picks constantly at the nails or tries to tear them off. It is not the same as onychophagia, where the nails are bitten or chewed, or dermatillomania, where skin is bitten or scratched. ...
,
nail-biting Nail biting, also known as onychophagy or onychophagia, is an oral compulsive habit of biting one's fingernails. It is sometimes described as a parafunctional activity, the use of the mouth for an activity other than speaking, eating, or drink ...
, frictional trauma, and even
carpal tunnel syndrome Carpal tunnel syndrome (CTS) is a nerve compression syndrome associated with the collected signs and symptoms of Pathophysiology of nerve entrapment#Compression, compression of the median nerve at the carpal tunnel in the wrist. Carpal tunn ...
if melanonychia is linked to anomalies of the nail plate or the periungual tissues. A common cause of symmetric melanonychia that affects the great toe, the lateral and external portion of the fourth or fifth toenail, is recurrent trauma from overriding toes or poorly fitting shoes. Skin disorders such
onychomycosis Onychomycosis, also known as tinea unguium, is a fungal infection of the nail. Symptoms may include white or yellow nail discoloration, thickening of the nail, and separation of the nail from the nail bed. Fingernails may be affected, but it is ...
,
paronychia Paronychia is an inflammation of the skin around the nail, often due to bacteria or fungi. Its sudden (acute) occurrence is usually due to the bacterium ''Staphylococcus aureus''. Gradual (chronic) occurrences are typically caused by fungi ...
,
psoriasis Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by patches of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small localized patches to complete b ...
,
lichen planus Lichen planus (LP) is a chronic inflammatory and autoimmune disease that affects the skin, nails, hair, and mucous membranes. It is not an actual lichen, but is named for its appearance. It is characterized by polygonal, flat-topped, violaceous p ...
,
amyloidosis Amyloidosis is a group of diseases in which abnormal proteins, known as amyloid fibrils, build up in tissue. There are several non-specific and vague signs and symptoms associated with amyloidosis. These include fatigue, peripheral edema, weigh ...
, and chronic radiodermatitis can cause
inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...
, which can activate
melanocyte Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the eye (the uvea), the inner ear, vagina ...
s and result in the formation of a light-brown band. Melanonychia frequently develops after the inflammatory process has resolved. Nonmelanocytic tumors such as subungual linear keratosis, verruca vulgaris, subungual fibrous histiocytoma,
basal cell carcinoma Basal-cell carcinoma (BCC), also known as basal-cell cancer, basalioma, or rodent ulcer, is the most common type of skin cancer. It often appears as a painless, raised area of skin, which may be shiny with Telangiectasia, small blood vessels ru ...
, myxoid pseudocyst, Bowen's disease, and onychomatricoma have also been shown to induce melanocytic activation, which leads to longitudinal melanonychia. Systemic-related melenonychia sometimes presents as numerous bands including the fingernails and toenails. Interestingly, cutaneous and mucosal pigmentation are frequently seen in conjunction with melanonychia linked to nutritional problems,
AIDS The HIV, human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a Preventive healthcare, pr ...
, and
Addison's disease Addison's disease, also known as primary adrenal insufficiency, is a rare long-term endocrine disorder characterized by inadequate production of the steroid hormones cortisol and aldosterone by the two outer layers of the cells of the adr ...
. Alcaptonuria, hemosiderosis, hyperbilirubinemia, and
porphyria Porphyria ( or ) is a group of disorders in which substances called porphyrins build up in the body, adversely affecting the skin or nervous system. The types that affect the nervous system are also known as Porphyria#Acute porphyrias, acute p ...
have all been linked to melanonychia. Medication (particularly
chemotherapy Chemotherapy (often abbreviated chemo, sometimes CTX and CTx) is the type of cancer treatment that uses one or more anti-cancer drugs (list of chemotherapeutic agents, chemotherapeutic agents or alkylating agents) in a standard chemotherapy re ...
drugs),
phototherapy Light therapy, also called phototherapy or bright light therapy is the exposure to direct sunlight or artificial light at controlled wavelengths in order to treat a variety of medical disorders, including seasonal affective disorder (SAD), circ ...
, radiation exposure from
X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
s, and electron beam therapy are examples of iatrogenic causes of melanocytic activation. Melanonychia linked with syndromes, such as Peutz-Jeghers, Touraine, and Laugier-Hunziker, usually affects numerous digits and is accompanied by mucosal pigmented macules including the lips and oral cavity. The most frequent cause of brown-black coloration on nails is
hematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is ...
s. It can be chronic (repeated, tiny trauma) or acute (after a single large trauma). Both dematiaceous and nondematiaceous fungi can induce fungal melanonychia; the most prevalent ones are
Trichophyton rubrum ''Trichophyton rubrum'' is a dermatophytic fungus in the phylum Ascomycota. It is an exclusively clonal, anthropophilic saprotroph that colonizes the upper layers of dead skin, and is the most common cause of athlete's foot, fungal infection of ...
and Scytalidium dimidiatum, followed by
Alternaria ''Alternaria'' is a genus of Deuteromycetes fungi. All species are known as major Phytopathology, plant pathogens. They are also common allergens in humans, growing indoors and causing hay fever or hypersensitivity reactions that sometimes lead t ...
and Exophiala.


Mechanism

While
melanocyte Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the eye (the uvea), the inner ear, vagina ...
s are found in the nail bed and matrix, most of them are dormant or quiescent.
Melanocyte Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the eye (the uvea), the inner ear, vagina ...
activation in response to trauma, infection, or inflammation starts the manufacture of
melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...
. Then,
melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...
-rich
melanosome A melanosome is an organelle found in animal cells and is the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom. Melanosomes are responsible for color and photoprotectio ...
s are transported by dendrites to the developing matrix cells. The nail plate becomes visibly pigmented when these matrix cells migrate in a distal direction and mature into nail plate onychocytes. Melanonychia can also be caused by proliferation of
melanocyte Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the eye (the uvea), the inner ear, vagina ...
s in the nail matrix, either with or without the formation of a nest (
nevus Nevus () is a nonspecific medical terminology, medical term for a visible, circumscribed, chronic (medicine), chronic lesion of the skin or mucosa. The term originates from , which is Latin for "birthmark"; however, a nevus can be either cong ...
)


Diagnosis

It is important to get a complete history, paying close attention to the beginning, development, and potential causes of melanonychia. All twenty nails, skin, and mucous membranes should be examined during the initial physical examination, bearing in mind all possible causes of brown-to-black nail coloration. It is best to rule out the possibility that an exogenous substance on top of or beneath the nail plate is the cause of the linear nail coloring. Using a dermoscopy can help determine whether a
biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, an interventional radiologist, or an interventional cardiology, interventional cardiologist. The process involves the extraction of sampling (medicine), sample ...
is required. Because melanonychia is typically difficult to diagnose clinically, a
biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, an interventional radiologist, or an interventional cardiology, interventional cardiologist. The process involves the extraction of sampling (medicine), sample ...
is usually required to rule out
melanoma Melanoma is the most dangerous type of skin cancer; it develops from the melanin-producing cells known as melanocytes. It typically occurs in the skin, but may rarely occur in the mouth, intestines, or eye (uveal melanoma). In very rare case ...
.


Classification

Longitudinal melanonychia or melanonychia striata is distinguished by a longitudinal brown-black/grey band that runs from the cuticle or nail matrix proximally to the nail plate's distal free edge. Diffuse or total melanonychia involves the entire nail palate. Transverse melanonychia is characterized by a transverse band across the nail plate's breadth.


Treatment

The underlying cause of melanonychia determines how to treat it. Regression of pigmentation may be brought on by the management of related systemic or locoregional diseases, the stopping of the offending medication, avoiding trauma, treating infections, or correcting nutritional inadequacies. Benign causes can be monitored and do not require treatment.


Epidemiology

About half of instances of chromonychia are caused by melanonychia. The most prevalent morphological pattern is longitudinal melanonychia.


See also

* Nail anatomy *
List of cutaneous conditions Many skin conditions affect the human integumentary system—the organ system covering the entire surface of the Human body, body and composed of Human skin, skin, hair, Nail (anatomy), nails, and related muscle and glands. The major function o ...


References


Further reading

* *


External links


DermNet

WebMD
{{Disorders of skin appendages Conditions of the skin appendages