Anatomy of the Nail

[Vincent.]

All about Nails.......


Anatomy of the Nail

Nails are KERATIN produced by a modified form of epidermis called NAIL MATRIX. Keratin is a protein complex which gives the nail its hard property. The NAIL PLATE grows from the nail matrix and this lies on the nail bed.

Functions of Nails

1. They protect the end of the digits.
2. In the fingers they are useful for picking up small objects and for scratching


ABNORMALITIES OF NAIL MATRIX

1. PITTING

When an inflammatory condition affects the nail matrix areas of abnormal keratin are formed.This abnormal keratin detaches itself from the nail plate leaving behind Pits or Ridges.

It is more easily seen on Finger nails.

Causes:

a. Isolated pits – in Normal nails

b. Psoriasis – small regular pits

c. Eczema – large and irregular pits with associated eczema around the nails.

d. Alopecia areata – small regular pits (If a patient with alopecia areata has pitting it is a poor prognosis for hair regrowth)


2. TRANSVERSE RIDGES

Causes:

a. Eczema

b. Chronic paronychia – this is mainly due to pressure on the nail matrix.

c. Beau’s lines

Beau’s line is a single line usually at the same place in all the nails. This is due to cessation of growth of nail matrix at the time of severe illness. After the illness, the matrix functions normally and the nail continues growing with a line in it.

3. LONGITUDINAL RIDGES

Causes – when a single nail is affected:

a. Median nail dystrophy

It is temporary and resolves spontaneously after a few months. Cause is unknown. It looks like a upside down Christmas tree in the centre of the nail.

b. Habit tic deformity

This is a broader ridge with numerous concave transverse ridges. It is mainly caused due to picking or biting the nail.

c. Ridge due to underlying myxoid cyst or wart in the posterior nail fold which presses on the underlying nail matrix.

Causes – when all nails are affected:

a. Few ridges – can be seen in Normal nails.

b. Lichen planus – fine and regular

c. Darier’s disease – fine and regular with notching of the end of the nail.

ABNORMALITIES OF THE NAIL BED

The nail bed is the area of epidermis situated under the nail which does not produce any keratin. Any abnormality in the nail bed causes discolouration under the nail

Causes:

1. Orange –brown colour - Psoriasis (Salmon Patches)

2. Red/purple/black colour

a. Splinter haemorrhage – small red longitudinal streaks seen in Sub acute bacterial endocarditis.

b. Sub ungual haematoma – due to bleeding under the nail following trauma. It is very painful

c. Sub ungual malignant melanoma

3. Brown colour

a. Junctional naevus

b. Malignant melanoma

4. Pink colour

a. Glomus tumour – benign tumour presenting as tender area under nail


5. White colour

Pallor of nail bed occurs in –

a. Hypoalbuminaemia

b. Chronic renal failure

ABNORMALITIES OF NAIL PLATE

A. Discolouration of the nail plate

Causes:

1. External staining – nicotine, medicines, hair dyes, nail varnish

2. Drugs

a. Chloroquine – Blue grey pigmentation
b. Penicillamine – yellow

3. White nails

a. White streaks due to minor trauma

b. Familial leuconychia – autosomal dominant – whole nail is white

c. Onycholysis – distal end of nail plate is broken off

4. Brown lines in nails

a. Junctional naevus

b. Malignant melanoma

5. White/ Yellow nails

a. Tinea – irregular thickened area

6. Yellow nail syndrome

a. All nails are yellow/green
b. Excessively curved
c. Rate of growth decreased – can cause onycholysis
d. Due to congenital abnormality of the lymphatics
e. Maybe associated with – Lymphoedema of legs or Bilateral pleural effusion

B. Thickening of the nail plate

a. Tinea

Dermatophyte fungi live on keratin and so actively multiply in the nail plate causing thickened and discoloured nails. It mainly affects toe nails.

Look for evidence of fungal infection in between toes and confirm by nail clippings.

b. Chronic trauma – mainly toe nails

ABNORMALITIES OF THE HYPONYCHIUM

ONYCHOLYSIS

This means the separation of the nail plate from the nail bed. This is due to abnormality of hyponychium – cos the nail plate is not firmly stuck onto the nail bed.

Causes –

1. Trauma – during manicure, excessive wetting, sub ungula haematoma

2. Psoriasis

3. Fungal infection

4. Poor peripheral circulation

5. Thyrotoxicosis

6. Allergic contact dermatitis


ABNORMALITIES OF THE CUTICLE

The cuticle joins the posterior nail fold to the nail plate and thus prevents bacteria from getting into the area around the nail.

If the cuticle is lost, infection can occur under the lateral or posterior nail fold causing PARONYCHIA.

1. Acute Paronychia

This is caused by infection with Staphylococcus aureus. It is associated with pain, redness, swelling and pus formation.

2. Chronic Paronychia

This is usually caused by Candida albicans and is more chronic. It has less swelling, no pus, and may have secondary infection.


ABNORMAL SHAPES OF NAILS

1. Over curvature

a. Clubbing
b. Hyperparathyroidism
c. Yellow nail syndrome

2. Spoon shaped nails (Koilonychia)

a. Iron deficiency anaemia
b. Normal – in small children

3. Wedge shaped nails

a. Pachyonychia congenita

It is a rare genetic abnormality. In this condition nail grows vertically and horizontally resulting in a wedge shaped nail.

4. Ingrowing toenails

When the nail penetrates the lateral nail fold it can cause redness, pain, pus and granulation tissue

LOSS OF NAILS

1. Temporary (without scarring)

a. Trauma
b. Beau’s lines – may break after severe illness

2. Permanent (with scarring)

a. Lichen planus – cuticle grows through the nail plate resulting in scarring. This change is called Pterygium

OTHER CONDITIONS SEEN AROUND NAILS

1. Viral warts
2. Myxoid cysts
3. Subungual and periungual fibromas
4. Subungual exostosis
5. Tumours – squamous cell carcinoma, malignant melanoma

NAIL CHANGES ASSOCIATED WITH SKIN DISORDERS

1. Psoriasis

Onycholysis, Nail pitting, Hyperkeratosis, Pustule and maybe occasional loss of nail.

2. Fungal

Discolouration, Onycholysis and thickening of the nail

3. Bacterial

Usually due to Staphylococcal and Pseudomonas infections – may give discolouration to the nails, paronychia.

4. Lichen Planus

Thinning of nail plate, Longitudinal ridges, pterygium

5. Alopecia areata

Pitting, thickening and ridging of nail (Sandpaper nail)

6. Dermatitis

Coarse pits, Ridging, Onycholysis

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Causes of Pigmented Streaks on Nails

1. Benign naevus

2. Physiological in Black skin

3. Traumatic

4. Laugier - Hunziker syndrome

5. Systemic diseases - Addison's, AIDS, Post adrenalectomy for Cushing's

6. Drugs - Mepacrine, Zidovudine, Busulphan, cyclophosphamide

7. Melanoma

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LAUGIER-HUNZIKER SYNDROME

It is described as acquired, benign macular hyperpigmentation of the lips and buccal mucosa frequently associated with longitudinal melanonychia (pigmented macules on the finger tips)

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Causes of Pterygium in Nails

1. Trauma

2. Lichen Planus

3. Chronic ischaemia

4. Radiotherapy exposure in nails

5. Nail patella syndrome

6. Dystrophic epidermolysis

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Causes of Koilonychia

1. Congenital

2. Trauma

3. Physiological - babies

4. Systemic diseases - Iron deficiency anaemia, Raynaud's disease, Lichen Planus, Alopecia areata, Syphilis, Endocrine disease.