Nails have several important functions. The nail plate acts as a protective shield for the fingertips; it assists in grasping and manipulating small objects. Our nails are also used for scratching, grooming, and cosmetic adornment.1
The nail unit is composed of the nail plate, nail matrix, nail folds, nail bed, and hyponychium (Figure 20-1A and B).1,2
Nail matrix: Forms the nail plate.
Nail plate: Hard, translucent, keratin-containing structure covering the dorsal surface of the distal digits on the hands and feet. Formed by the nail matrix, the nail plate grows out from under the proximal nail fold. The nail usually appears pink, which is due to the underlying vasculature of the nail bed. The small, white, semi-circular structure at the proximal portion of the nail is the lunula, which is the visible portion of the nail matrix.
Nail bed: Structure underlying the nail plate, which contributes to the nail plate’s ability to attach to the finger.
Hyponychium/onychodermal band: Under the distal free edge of the nail. The hyponychium is the transition point between the nail and the normal skin of the digit. The onychodermal band is the point of strongest attachment between the nail and the underlying digit.
Nail folds: Proximal and lateral. These are epithelial structures. The cuticle protects the matrix by sealing off the potential space between the nail plate and the proximal nail fold.
Nail disorders can be difficult to differentiate from one another. To determine the correct diagnosis takes practice and often laboratory studies such as fungal cultures. To add to the confusion, many nail disorders can have secondary fungal or bacterial infections.
Examples of specific diseases in each category include:
✓ Infectious: Dermatophyte, candida, mold, and bacteria.
✓ Papulosquamous: Psoriasis and lichen planus.
✓ Traumatic: Habit tic, some cases of onychodystrophy or onycholysis.
✓ Systemic: Yellow nail syndrome, clubbing, and Beau’s lines.
✓ Tumors: Squamous cell carcinoma, melanoma, and benign tumors.
Tumors involving the nail unit are an important category of nail disorders. These are covered in other sections of this textbook are covered in Chapters 16, 17 and 18.
A differential diagnosis of nail disorders and clinical findings that distinguish them from one another are presented in Table 20-1.
| Nail Disease | Clinical Findings |
|---|---|
| Infectious | |
| Onychomycosis | Brown, yellow, orange or white discoloration, thickened nail plate, subungual hyperkeratosis, onycholysis |
| Pseudomonas infection | Green or black discoloration of nail plate. Onycholysis is usually present. Paronychia is common |
| Papulosquamous | |
| Psoriasis | Nail matrix involvement: Pitting is broader and more irregular than pitting due to alopecia areata, leukonychia, erythema of lunula, crumbling of nail plate Nail bed involvement: Discoloration (oil drop—yellow or salmon patch—red), splinter hemorrhage, subungual hyperkeratosis, or onycholysis |
| Lichen planus | Thinning of nail plate with longitudinal ridging and fissuring. Dorsal pterygium is almost pathognomonic for nail lichen planus. The matrix is scarred and the nail plate is divided into two distinct sections |
| Associated with systemic diseases | |
| Beau’s lines | Horizontal, depressed, white, nonblanching bands of the nail plate. Can be caused by systemic insults, drugs, or trauma |
| Clubbing | Overcurvature of the nail. Can be idiopathic or related to cardiovascular, pulmonary, or gastrointestinal disorders |
| Koilonychia | Also called spoon nails. The center of the nail is depressed relative to the edges. Can be caused by iron deficiency, hypothyroidism, trauma, or be congenital |
| Half and half nails | Also called Lindsay’s nails. The proximal half of the nail is normal or white and the distal half is darker. Can be caused by renal disease |
| Mee’s lines | Single or multiple transverse white lines, usually present on all nail plates. Classically caused by arsenic poisoning, but can be the result of many other systemic insults |
| Splinter hemorrhage | Small, longitudinal lines of dark discoloration. Should grow out with the nail plate. Usually caused by trauma, but can be related to systemic illnesses, or drugs. If the lesions occur distally on a single nail, it is less likely to be related to a systemic cause |
| Terry’s nails | The nails are white proximally, with a narrow pink or brown distal band. Can be related to liver disease or aging |
| Yellow nail syndrome | Diffuse yellow, thickened nail plates. Most commonly seen with lung disease and chronic lymphedema |
| Other | |
| Alopecia areata | Superficial, regular, geometric pitting most common. The pitting is much more regular than pitting due to psoriasis |
| 20-Nail dystrophy (trachyonychia) | Nails have a roughened surface, longitudinal ridging, and thinning. Nail plates have a sandpaper appearance Look for skin or hair abnormalities suggestive of lichen planus, psoriasis, or alopecia areata to help identify the underlying cause |
| Habit tic deformity | Roughly parallel, horizontal depressions most often over the median nail plate |
| Onycholysis | Nail plate appears white due to air between the nail plate and nail bed |
Dermatophyte, mold, and candida infections of the nails are common causes of nail disorders. They closely resemble other nails disorders such as psoriasis. Fungal infections of the nails are covered in Chapter 10.
Bacteria can also infect the nail unit. Pseudomonas is a common colonizer of onycholytic nails.2 The affected nail is usually discolored green or black (Figure 20-2). Patients often have a history of wet-work. Bacterial cultures of pus or nail clippings can confirm the diagnosis. Treatment involves trimming the onycholytic portion of the nail and the use of one of the following topical therapies: soaking affected nails 2 to 3 times a day in a dilute bleach solution (2% sodium hypochlorite) or half-strength vinegar, solution; and application of polymyxin B, chlorhexidine solution, 15% sulfacetamide, gentamicin or chloramphenicol ophthalmological solution or octenidine dihydrochloride 0.1% solution for 4 weeks or until resolved.2,3 Systemic antibiotics should not be administered unless there are signs of cellulitis.
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