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ลักษณะโครงสร้างของเล็บ
   Nail Anatomy

ความผิดปกติของเล็บจาก
  การแพ้/ สัมผัส กับสารเคมี
  Aging
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  เชื้อรา
  Fungi
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  ยิสต์และแบคทีเรีย
  Bacteria & Yeast
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  การถูกกระแทก
  Trauma
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  โรคสะเก็ดเงิน
  Psoriasis
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  เอคซีม่า
  Eczema
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  เชื้อไลเคนส์
  Lichen planus
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  โรคอื่นๆที่มีผลต่อเล็บ
  Internal
 

	Health Navigation

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Nail plate. The nail plate consist of hard, translucent, keratin. The bulk of the keratin 
is derived from, the matrix. Two structures are seen through the translucent keratin, the white half-moon shaped lunula (matrix) and the pink nail bed. The nail bed appears pink because it contains a rich vascular network.

Matrix.  The matrix is a highly specialized epithelial structure that manufactures the bulk of the nail plate. It grows and matures like other epithelial structures and produces a highly dense and compacted stratum corneum called the nail plate. The flat, oval shaped, matrix extends from under the proximal nail fold to just beyond the proximal portion of the visible part of the nail plate. A little more than one-third of the matrix is seen through the nail plate as the white half-moon shaped lunula. The epithelium of the proximal nail fold and the proximal portion of the matrix under the nail fold makes the top portion of the nail plate. The distal matrix (lunula) makes the bottom of the nail plate that is bonded to the nail bed.

Nail bed. The highly vascular bed is the epithelium under the plate that begins at the distal lunula and ends near the tip of the finger at the hyponychium. The surface consists of parallel longitudinal ridges extending distally from the lunula to the finger tip. The ridges fit into underlying dermal grooves. The higher dermal ridges fit into the nail bed grooves and contain blood vessels that when affected by trauma or disease produce the unique bleeding patten called splinter hemorrhages. When bleeding is confined to the dermal grooves it appears as a line of blood when seen through the nail plate.

Hyponychium. The nail plate ends and looses its bond to the nail bed at the hyponychium. The hyponychium is that short portion of epidermis that extends from the distal nail bed to the distal groove. Itís stratum corneum may accumulate under the nail plate tip.

Distal Groove. The distal groove is a semicircular depression in the epidermis at the distal part of the hyponychium. It marks the boundary between the nail unit and the finger tip.

Proximal nail fold. The proximal nailfold is the skin that overlies the matrix. The keratin from its surface streams out onto the nail plate to form the cuticle. Capillary loops at the tip of the proximal nailfold are normally small and inapparent, but they become distinct in diseases such as systemic lupus erythematosus and scleroderma. The fold covers the proximal nail plate for a few millimeters and then makes a 180-degree turn and curves back into direct contact with the nail plate. The keratin of this portion of the nail fold becomes the surface of the nail plate.  It makes another 180-degree turn and becomes continuous with the nail matrix.

Lateral nail fold. The lateral nail fold is a longitudinal depression at the sides of the finger that contain and the lateral edges of the nail plate.

Cuticle. The cuticle is the stratum corneum of the proximal nail fold that extends and adheres to the proximal nail plate. It forms a barrier and seal preventing moisture, bacteria and yeast from entering the potential space between the nail plate and the proximal nail fold. This important structure should not be cut or manipulated. It may be permanently destroyed by manipulation or excessive wetting.

Physiology
Growth rates. Fingernails grow faster than toenails. Fingernails grow about 0.1 mm/day or 3 mm/month. Toenails grow about 1 mm/month. It takes approximately 5.5 months for a fingernail and 12 to 18 months for a toenail to grow from the matrix to the free edge. Children under 14 have faster growth rates than adults. A reduction in the rate of matrix-cell division occurs during chemotherapy, retinoid therapy  and with systemic diseases such as scarlet fever. Temporary reduction in matrix-cell growth rates causes a  thinning of the nail plate and creates a horizontal groove called Beauís lines. The depth of the groove indicates the degree of growth reduction. Nails that become partially separated from the anterior nail bed (onycholysis) grow faster.

Aging may increase or decrease nail thickness. The shape and opacity of the nails varies among individuals. Nail splitting, and longitudinal ridging and beading are signs of aging.

Distal plate splitting (brittle nails) The splitting into layers or peeling of the distal nail plate may resemble or be analogous to the scaling of dry skin . This nail change is found in approximately 20% of the adult population and is more common in older people. Repeated water immersion increases the incidence of brittle nails, particularly in women. Prevention Protection with rubber-over-cotton gloves and application of heavy lubricants directly to the nail plate provide improvement. Treatment Local measures to rehydrate the nail plate should be initiated. After the nails have been soaked in water at bedtime, a moisturizer (e.g., an alpha-hydroxy acid or a lactic acid such as Lac-Hydrin) should be applied. The moisturizing agent may be applied under occlusion with a white cotton glove or sock. Nail enamel may slow the evaporation of water from the nail plate. It should be removed and reapplied no more than once a week. Patients with brittle nails who receive the B-complex vitamin, biotin, (2.5 mg/day) may improve and have up to a 25% increase in nail-plate thickness.

Longitudinal ridging and beading
The nail plate surface is smooth in young people.

Longitudinal ridging
Longitudinal ridging is a common finding in people over the age of 50, but this variant is observed in younger people. Elevated ridges extend from the proximal nail fold to the distal nail plate. The ridges may be very prominent in the elderly. One but usually several ridges are present.

Longitudinal beading
Semicircular beads occurs at all ages but are more common  in the elderly. The beads are arranged longitudinally in one or several lines.

Introduction

Fungal infections of the nail are called onychomycosis. Fungal organisms invade the nail plate and cause a variety of signs and symptoms. These infections are common in the elderly but occur in children. They cause changes in the nail color and thickness. Nail fungal infections may cause pain, secondary infection with bacteria and are a source of embarrassment. Trauma predisposes to infection. There is a definite hereditary predisposition. 

There is a tendency to label any process involving the nail plate as a fungal infection. Many cutaneous diseases such as psoriasis and onycholysis (nail plate separation) can change the structure and color of the nail and appear to be infected.

Incidence. Onychomycosis is a relatively new disease. It was rarely seen prior to the 1920s. Today it is seen in people of all ages. The incidence increases in the elderly and is higher in men. It occurs in over 20% of people over the age of 40. Toenail are infected much more often then fingernails. People with nail infections often are infected at other sites such as the groin and on the palms. Onychomycosis accounts for about 50% of nail disease.

Predisposing factors. Fungi thrive in a warm moist environment such as exits in shoes. Fungi are present on the wet floors of communal exercise facilities. HIV infection, immunosuppressive therapies, systemic antibiotics and chemotherapeutic agents all encourage fungal growth.

Symptoms. Thick nail can case pain and functional limitation especially when compressed by shoes. Secondary bacterial infections cause swelling of the surrounding and underlying ski

Psychosocial impact. Comparatively speaking patients with fungal nail infections 
have poorer general health, difficulty with social interactions and a poor self image.

Economic impact. Patients with pain and physical limitations perform poorly at work 
and may miss work. There are costs for doctors visits, laboratory tests and medication

Patterns of infection

There are 4 patterns of nail fungal infection. Several patterns of infection may occur simultaneously in the nail plate. Each type is associated with a different point of entry of the fungus. In order of frequency they are:

1. Distal subungual onychomycosis-fungi invade the distal nail bed area
 Distal subungual onychomycosis
1. The most common pattern of nail invasion.
2. The dermatophyte fungus Trichophyton rubrum is the most common pathogen.
3. The fungus invades the nail bed through the tip of the finger and causes  
     hyperkeratosis which may eventually force the nail plate to separate from the 
     nail bed (onycholysis).
4. The fungus enters the undersurface of the nail plate and invades through the hard 
    keratin at variable rates. Only a small portion of the nail plate may be involved or the 
    entire plate may become infected.
5. The nail plate changes color, usually yellow, dark brown or white.
6. Hyperkeratotic debris causes the nail to rise and put pressure on shoes.
7. The nail plate also thickens. Nail structural integrity is compromised and the nail 
     plate fragments and crumbles

2. White superficial onychomycosis-fungi invade 
the nail plate surface.
 White superficial onychomycosis
1. Most often caused by Trichophyton mentagrophytes.
2. Fungus invades directly through the surface of the nail plate.
3. The plate surface becomes soft, dry and powdery.
4. The entire nail plated may become involved.
5. The nail plate does not get thicker and does not separate from the nail bed

3. Proximal subungual onychomycosis-fungi invade the proximal nail fold.
 Proximal subungual onychomycosis
1. The dermatophyte fungus Trichophyton rubrum is the most common pathogen.
2. The fungus invades through the proximal nail fold and cuticle, migrate to the 
     underlying matrix and finally invades the nail plate from below.
3. The nail plate may thicken but the surface remains intact.
4. Hyperkeratotic debris accumulates under the nail and may cause the nail to 
     separate from the nail bed.
5. Most common pattern seen in patients with HIV infection. Very uncommon in  normal 
     immunocompetent people

4. Candida onychomycosis-fungi invade the distal nail plate.
 Candida onychomycosis
1. Caused most often by Candida albicans.
2. The yeast invades the distal end of the nail plate.
3. Almost always limited to patients with the rare syndrome chronic mucocutaneous 
    candidiasis.
4. Generally involves all fingernails and toenails.
5. Entire nail plate becomes thick  and turns yellow

Causes of nail fungal infections

The dermatophyte fungi, Trichophyton rubrum accounts for over 90% of nail plate infections. Less than 8% of infections are cause yeast and about 2% are cause by the nondermatophyte molds such as Aspergillus, Fusarium and Scopulariopsis. They may be found in any pattern of nail infection, especially distal subungual onychomycosis and white superficial onychomycosis. The molds do not respond to griseofulvin or the newer oral antifungal agents.