2. Introduction
An appendage of the skin better known as the Nail Unit
A translucent, protective plate that protects the tips of the fingers
and toes
Onyx is the technical term for nail
Onychology is the study of nail
3. Development of Nail
9 weeks
• First embryonic rudiment of the nail unit becomes evident,
known as the nail anlage
10 weeks
• Primary nail field becomes evident as a distinct region
13 weeks
• Proximal and lateral nail folds differentiate due to a
differential growth of the primary nail field and its adjacent
tissues
14 weeks
• The nail plate is formed, and emerges from beneath the
proximal nail plate
5. 1. Nail Plate
It is the visible part of the nail and its free edge extends beyond the distal end of the digits
The nail plate is formed by keratinisation of the nail matrix cells which loose their nuclei and get progressively
elongated and compacted with minor contribution from the nail bed
The nail plate is a fully keratinized structure consisting of:
1. Onychocytes
2. Hard Keratins
3. Phosphate
4. Calcium
It comprises three horizontal layers:
1. A thin dorsal lamina
2. The thicker intermediate lamina
3. A ventral layer from the nail bed
6. Chemical Properties of the Nail Plate
The nail plate, like hair, consists mainly of fibrillary low-sulfur protein, globular
high-sulfur matrix protein and high-glycine/tyrosine rich matrix protein.
The nail matrix, and hence the nail plate, express hard keratins.
The nail bed, nail matrix and nail plate expresses epithelial/ soft keratins.
However, these areas do not express the keratins 1 and 10 like the suprabasal
epidermis.
The flexibility of nail plate is related to its water content.
7. 2. Nail Matrix
Germinative epithelium of the nail unit, located above mid distal phalanx.
The nail matrix has 2 portions:
1. Proximal Matrix
2. Distal Matrix
It has the following cells:
1. Melanocytes
2. Langerhans Cells
3. Merkel Cells
4. No Granular Layer
8. 3. Nail Bed
The nail bed consists of the dermis and the soft tissue that lie
beneath the nail plate.
The epithelium is thin and consists of two to five cell layers.
The nail bed also has a minor contribution to the nail plate
formation.
Its keratinization is also not associated with a granular layer.
9. 4. Eponychium
It is also known as the cuticle
A strip of cornified epithelium that acts as a seal.
It emerges from the proximal nail fold and
subsequently adheres to the superficial surface of
the proximal nail plate.
10. 5. Hyponychium
Keratotic natural barrier at the physiological point of
separation of the nail plate from the underlying distal nail
fold
It seals the free edge, preventing external moisture,
bacteria, or fungi from getting under the nail
11. 6. Nail Folds
They ensheathe and hold the nail plate in
place.
1. Proximal Nail Fold
2. Distal Nail Fold
3. 2 Lateral Nail Folds
12. 7. Nail Isthmus
In the distal part of the nail, a transverse band is seen which is
more pink (or brown) than the rest of the nail-bed. This is called the
onychodermal band.
Proximal to this pink band is a transverse white zone, namely the
onychocorneal junction which represents the most distal point of
attachment between the nail bed and the nail plate.
The onychocorneal junction, in histology, corresponds to a
transitional zone between the nail bed and the hyponychium called
the nail isthmus
13.
14. Blood and Nerve Supply
The nail apparatus has an abundant blood supply
provided by the lateral digital arteries.
The nail-fold capillary network can be visualized using a
dermoscope over the proximal nail fold. The morphology
of these capillary loops are important in conditions such
as scleroderma and dermatomyositis
The nerve supply is through sensorimotor nerves which
run parallel to the digital vessels. The origin of the nerve
supply is from the dorsal branches of paired digital
nerves.
15. Nail Growth
Growth of nail plate is a continuous process that happens throughout
life, with the newly formed plate moving distally.
This continuous distal movement is aided by two factors— proximal
proliferation and differentiation of nail matrix keratinocytes and the nail
epithelium which drags the nail plate forward like a conveyor belt.
The mean growth rate of the nail plate is 1.5 mm per month for toenails
and 3.5 mm per month for fingernails.
The total regeneration time for a fingernail is around 6 months and 12–
18 months for toenails.
16. Functions of Nail
1. Aesthetics of the hand
2. Protection of the distal phalanges
3. Tactile discrimination and the capacity to pick up small objects
4. Scratching
5. Grooming
6. As a weapon
7. Normal biomechanics of gait
9th week It is seen as a specialized area of epidermis overlying the dorsal tip of the digit
By the 17th week, the nail plate covers the nail plate completely
The nail plate continues to grow till death
Onychocytes - closely packed, adherent, interdigitating cells that lack nuclei or organelles and are arranged in a lamellar pattern
Hard Keratins - rich in sulphur-containing amino-acids and are responsible for the mechanical resilience of the nail plate. The nail matrix is responsible for the formation of the hard keratin of the nail plate.
Apart from this, nail plate contains significant amounts of phospholipids and is rich in calcium, found as the phosphate in hydroxyapatite crystals.
The proximal part of finger nails shows a whitish, opaque, half-moon-shaped area, the lunula, which is the visible portion of the nail matrix.
Keratins 6a, 6b, 6c, 16 and K17 (soft keratins)
The normal water content of the nail plate is 18%
The proximal part of the nail matrix, under the proximal nail fold, forms the dorsal surface of the nail plate. The bulk of the nail plate is formed by the proximal matrix, which contributes 81% of the cells in the nail plate.
The distal nail matrix, the lunula, forms the ventral aspect of the nail plate, and has a smaller contribution to the nail plate.
Hence, a biopsy of the proximal matrix is more likely to produce nail dystrophy.
Melanocytes are located above the basal layer in the nail matrix and are usually amelanotic. The distal matrix melanocytes may get activated and produce longitudinal melanonychia.
Langerhans cells and Merkel cells are also present in the distal part of the nail matrix.
The granular layer is absent from the nail matrix (and nail bed), unlike the nail folds.
The proximal nail folds are similar in structure to the adjacent skin but are devoid of dermatoglyphic markings and pilosebaceous glands. It comprises of sweat glands and has dorsal and ventral folds.
onychocorneal junction aka white band of pinkus
The isthmus, which may not be clearly seen in a normal nail, is prominent in disorders affecting the nail, such as pachyonychia congenita and inverse pterygium
Diagram of a sagittal section through the nail unit
Toe nails protect the distal toes and support these tissues during walking. Therefore, the toe nails are necessary for the normal biomechanics of gait
The normal nail plate surface is smooth, shiny, and convex
Beau’s lines appear as transverse depressions on the nail plate surface, which may have variable depth and length. These are the most common and least specific nail change. Causes include trauma involving proximal nail fold, severe acute illness, exposure to extreme cold, psychological stress, poor nutritional status.
refers to the prominent-appearing longitudinal bands over the nail plate surface. It is due to alternate thickening or thinning of the nail plate, resulting in fragile or brittle nails which tend to break easily at the distal end. Causes include Lichen planus, pityriasis rubra pilaris, anemia, excessive water exposure.
a refers to the rough, sandpaper appearance of nails. It is a combination of fine pitting, onychorrhexis, and lamellar splitting in various proportions presenting as rough, longitudinally ridged nails (opaque trachyonychia) or, less frequently, as uniform, opalescent nails with pits (shiny trachyonychia). Causes include Idiopathic, alopecia areata, nail psoriasis, nail lichen planus, eczematous conditions.
Pits are punctate depressions on the nail plate surface, appearing as small, irregular or regular, round holes. Causes include Psoriasis, lichen planus, eczematous conditions, chronic renal failure, chronic paronychia.
A normal nail plate is rectangular in shape with a convex surface that slopes down gently toward its edges.
seen more in toenails. Depending on the degree as well as the regularity, there are three main types of overcurved nails, viz. pincer nails, tile-shaped nails, and “plicated” nails. The nails are transversally hypercurved, with their lateral edges traumatizing the lateral folds and causing pain. Causes include genetic predisposition, ill fitted shoes, subungual exostosis, inflammatory osteoarthritis, etc.
Progressive flattening and further concavity of the nail plate surface are known as platonychia and koilonychia respectively. In koilonychia, the nail is concave withedges, hence the term “spoon nail”. It can be a normal finding in children up to 3–4 years of age as the nail plate is thin. It is less common in adults and occurs in the fingernails of manual workers in contact with irritants and detergents that damage the nail plate. Anemia is often associated with koilonychia
Can be congenital or acquired. Congenital – syndromes- nail patella syndrome. Acquired- trauma, inflammatory – lp, pemphigus, drugs, eterinate
nail is hypercurved, both transversally and longitudinally, accompanied by soft tissue hypertrophy of digital pulp. clubbing is indicative of several respiratory and cardiac diseases. Pseudoclubbing - overcurvature of the nails in both the transverse and longitudinal axes with preservation of a normal Lovibond’s angle
Pachyonychia is diffuse nail thickening along with loss of its normal nail transparency. Pachyonychia congenita is a rare autosomal-dominant disorder. Acquired causes - chronic friction, gait abnormalities, or even infections
The normal nail plate surface is smooth, shiny, and convex
Leukonychia is the whitish appearance of the nail plate
condition is characterized by brown-to-black nail pigmentation. A) racial cause b)derma - Onychomycosis, paronychia, psoriasis, lichen planus c) local causes- frictional trauma, illfitting shoes d) systemic - Addison’s disease, HIV, nutritional, porphyrias e) iatrogenic- Chemotherapeutic agents, phototherapy, etc.
longitudinal red band, commonly originating at the level of the lunula and reaching up to the distal border. Causes of localized longitudinal erythronychia include local processes and tumors such as onychopapilloma. Other benign causes could be a verruca, warty dyskeratoma, or a glomus tumor. Malignancies such as squamous cell carcinoma in situ, melanoma in situ, or basal cell carcinoma can also present with longitudinal erythronychia. In cases with polydactylus longitudinal erythronychia, a systemic cause or inflammatory disorder is causative include Darier’s disease, nail lichen planus, systemic amyloidosis, and graft-versus-host disease, etc
The nail plate is normally tightly adherent to the nail bed
presents as a distal separation of the nail plate from the nail bed, resulting in the disruption of the onychodermal band with the distal nail plate appearing opaque or discolored. causes of onycholysis include congenital onycholysis, photo-onycholysis (associated with porphyria or drug-induced), epidermolysis bullosa, psoriasis, etc
accumulation of scales under the nail plate, which becomes detached and uplifted. Various inflammatory disorders such as psoriasis, contact dermatitis, and distal subungual onychomycosis result in subungual hyperkeratosis due to excessive proliferation of nail bed or hyponychium keratinocytes.
Paronychia refers to inflammation of the soft tissue folds surrounding the nail plate. It can be of two types, acute or chronic. Patients with acute inflammation complain of erythema, tenderness, swelling, or accumulation of fluid underneath the nail folds. In chronic cases, the nail fold gets thickened and rounded off due to repeated bouts of inflammation.
Scleroderma pattern with tortuous and dilated capillaries; capillary dropouts; and microhemorrhages. Other conditions where similar patterns can be present include dermatomyositis, mixed connective tissue disease, Raynaud’s phenomenon, etc
