In animals and birds claws are used for digging and grasping as well as for fighting.
The human nail may be used as a weapon but its main function is to protect the distal soft tissues of the fingers and toes.
As an ectodermal derivative composed of keratin, the nail plate grows forward from a fold of epidermis over the nail bed which is continuous with the matrix proximally.
The keratin composing the nail is derived mainly from the matrix with contributions from the dorsal surface of the nail fold, and the nail bed also adds keratin to the deep surface.
The nail grows slowly for the first day after birth then more rapidly until it slows in old age.
The rate of nail growth is greater in the fingers than the toes, particularly on the dominant hand.
It is slower in women but increases during pregnancy. Finger nails grow at approximately 0·8 mm per week and toe nails 0·25 mm per week.
Physical signs in the nails
The changes in the nail may be due to a local disease process, a manifestation of a skin disease, or a systemic disorder.
Hereditary disorders may also affect the nails.
It is therefore important to take both a general history and specifically enquire about skin diseases.
It sometimes happens that the nail changes are the only sign of a dermatological disease, although the patient may have a previous history of lichen planus or psoriasis, for example.
Localised infection or trauma will affect one or two nails.
Skin disease, such as psoriasis, affects many or all nails, usually symmetrically, whereas systemic illness or drugs will affect all the nails. Local nail changes
Trauma
• Acute trauma.
This may remove the whole nail.
• Chronic trauma as a result of badly fitting footwear may cause thickening of the nail with deformed growth, onychogryphosis.
Chronic trauma due to overenthusiastic manicuring or habitual picking at finger nails can result in deformity and impaired growth.
• Repeated trauma in occupations that involve repetitive action, such as assembling cardboard boxes, may cause detachment of the nail (onycholysis) or splitting of the nails.
Infection
• Infection of the tissues around the nail (paronychia) is often mixed with pyogenic organisms, including pseudomonas, as well as yeasts such as candida.
This condition occurs most frequently in those employed in the food industry and occupations where there is repeated exposure to a moist environment and minor trauma.
The index and middle fingers are most frequently involved.
• Infection of the nail plate itself occurs in fungal infections, which are commonly due to Trichophyton or Epidermophyton species.
• Those living in the tropics may acquire infection with Scopulariopsis brevicaulis, which produces a black discoloration of the nail.
Skin diseases affecting the nails
Since the nail plate consists of specialised keratin produced by basal cells, it is not surprising that it is affected by skin diseases.
Some conditions, such as psoriasis, may produce characteristic changes whereas in other conditions, such as eczema, the changes are much less specific.
Psoriasis causes an accumulation of keratin, as in lesions of the skin.
This may result in the nail being both thickened and raised from the nail bed (onycholysis).
There may be the changes of pustular psoriasis in the surrounding tissues, indistinguishable from acrodermatitis pustulosa.
Loss of minute plugs of abnormal keratin results in “pitting”.
Lichen planus produces atrophy of the nail plate which may completely disappear.
The cuticle may be thickened and grow over the nail plate, known as pterygium formation.
Eczema may be associated with brittle nails that tend to split.
Thickening and deformity of the nail occurs in eczema or contact dermatitis, sometimes with horizontal ridging.
Darier’s disease results in dystrophy of the nail and longitudinal streaks which end in triangular-shaped nicks at the free edge.
On the skin there may be the characteristic brownish scaling papules on the central part of the back, chest, and neck. These are made worse by sun exposure.
Alopecia areata is quite often associated with changes in the nails including ridges, leuconychia, and friable nails.
It may be associated with “20 nail dystrophy”.
Autoimmune conditions such as pemphigus and pemphigoid may be associated with a variety of changes including ridging, splitting of the nail plate, and atrophy in some or all of the nails.
Discoloration of the nail and friability are associated with lupus erythematosus.
General diseases affecting the nails
Nail changes in systemic illness
Acute illness results in a transverse line of atrophy known as a Beau’s line.
Shedding of the nail, onychomedesis, may occur in severe illness.
Chronic diseases
Clubbing affects the soft tissues of the terminal phalanx with swelling and an increase in the angle between the nail plate and the nail fold.
It is associated with chronic respiratory disease, cyanotic heart disease, and occasionally in chronic gastrointestinal conditions.
It is occasionally hereditary and may be unilateral in association with vascular abnormalities.
Colour changes
All the nails may be white (leukonychia) due to hypoalbuminaemia in conditions such as cirrhosis of the liver. Brown discoloration is seen in renal failure and the “yellow nail syndrome”, may be associated with abnormalities of the lymphatic drainage.
The nail may have a yellow colour in jaundice.
Drugs may cause changes in colour, for example tetracycline may produce yellow nails, antimalarials a blue discolouration, and chlorpromazine a brown colour.
Leuconychia or whiteness of the nails occurs in fungal infections.
Small white spots on the nail are quite commonly seen and are thought to be due to trauma of the nail plate.
Longitudinal pigmented streaks result from increased melanin deposition in the nail plate.
Longitudinal brown streaks are frequently seen in individuals with racially pigmented skin, particularly after trauma.
This is rare in caucasians but occurs as a result of a benign pigmented naevus at the base of the nail and in associated lentigo.
The most important cause to remember is subungual melanoma, which may present with a longitudinal deep brown or black streak.
Hutchinson’s sign with pigmentation extends into the surrounding tissues, particularly the cuticle.
Adrenal disease may rarely be associated with longitudinal streaks.
Thickening of the nail plate may be due to hyperkeratosis in psoriasis, in which case the changes will be symmetrical and there may well also be pitting of the nail and onycholysis.
Similar changes are seen in fungal infection of the nail, which may be symmetrical on the toes. Nail clippings should be sent for microscopy and mycological culture.
Hypertrophy of the nail plate occurs as a result of chronic trauma, with only a few nails affected, and is usually seen in the feet.
Pachyonychia congenita is a rare congenital disorder characterised by hypertrophic nails.
Hyperkeratosis, due to the accumulation of keratin under the nail plate, is also seen in psoriasis.
It occurs occasionally in association with chronic dermatitis.
Detachment of the nail plate (onycholysis)
• Psoriasis
• Fungal infection
• Trauma
• Thyrotoxicosis.
Onycholysis is due to a detachment of the nail from the nail bed.
If it is extensive, there may be complete loss of the nail plate.
It is most commonly seen in psoriasis and occasionally in fungal infections of the nail.
It may occur as a result of trauma or thyrotoxicosis.
Pitting of the surface of the nail plate
• Psoriasis
• Alopecia Pitting of the nail plate is due to punctate depressions on the surface of the nail plate.
They are most often seen in psoriasis but may occur in alopecia areata.
Horizontal ridging
• Beau’s lines may be seen after systemic illness and acute episodes of hand dermatitis.
Longitudinal ridging
• Single due to pressure from nail fold tumours
• Multiple due to lichen planus
• Alopecia areata
• Psoriasis
• Darier’s disease.
Ridging represents a disturbance of nail growth.
Inflammation as seen in acute paronychia or trauma can result in a single nail developing a horizontal ridge.
After an acute illness there may be horizontal lines on all the nails.
The lines may also occur with eczema.
A single longitudinal ridge can result from pressure due to benign or malignant tumours in the nail fold.
A mucoid cyst can produce a longitudinal ridge.
Multiple longitudinal lines are characteristic of lichen planus, psoriasis, alopecia areata, and Darier’s disease. Koilonychia is a concave deformity of the nail plate, generally occurring in the finger nails.
It may be idiopathic or occur as a result of iron deficiency anaemia.
Lesions adjacent to the nail
Mucoid cysts develop subcutaneously over the distal interphalangeal joint and may be adjacent to the nail, producing abnormalities of growth.
These cysts develop as an extension of the synovial membrane and are linked to the joint by a fine tract.
Very careful excision is required for a cure. Naevi may occur adjacent to the nail and a benign melanocytic naevus can produce a pigmented streak.
Subungual melanoma may produce considerable pigmentation of the nail and often causes pigmentation of the cuticle, so called
Hutchinson’s sign.
Sometimes subungual melanoma is amelanotic so there is no pigmentary changes and any rapidly growing soft tumour should raise suspicions of this condition.
Subungual exostosis can cause a painful lesion under the nail.
It is confirmed by x ray examinations. Glomus tumours arise as tender nodules.
Periungual fibrokeratomas also develop in patients with tuberous sclerosis.
Treatment of nail conditions
It is clearly not possible to treat congenital abnormalities of the nail, but avoiding exposure to trauma may help.
Nail changes associated with dermatological conditions may improve as the skin elsewhere is treated.
Systemic treatment of associated dermatoses will of course tend to improve the nail as well, for example methotrexate or retinoids for psoriasis. Infective lesions respond to antifungal or antibiotic treatment.
In chronic paronychia there is often a mixed infection and a systemic antibiotic combined with topical nystatin may be required.
It is also important to keep the hands as dry as possible.
The imidazole antifungal drugs are fairly effective but are fungistatic.
Terbinaline is fungicidal and a short course is as effective as prolonged treatment with the older drug griseofulvin.
