Nail Diseases

Anatomy

The nail unit consists of several components ( Fig. 25.1 ). The nail plate is hard, translucent, dead keratin. The nail fold includes the skin surrounding the lateral and proximal aspects of the nail plate. The proximal nail fold overlies the matrix. Its keratin layer extends onto the proximal nail plate to form the cuticle. Capillary loops at the tip of the proximal nail fold are normally small and nonapparent, but they become distinct in diseases such as systemic lupus erythematosus and scleroderma. The proximal nail fold epithelium 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. It makes another 180-degree turn and becomes continuous with the nail matrix.

The matrix epithelium synthesizes 90% of the nail plate. The lunula (white half-moon), which is visible through the nail plate, is the distal aspect of the nail matrix. It is continuous with the nail bed. The nail bed extends from the distal nail matrix to the hyponychium. As the nail streams distally, material is added to the undersurface of the nail, thickening it and making it densely adherent to the nail bed. The nail bed consists of parallel longitudinal ridges with small blood vessels at their base ( Fig. 25.2 ). Bleeding induced by trauma or vessel disease, such as lupus, occurs in the depths of these grooves, producing the splinter hemorrhage pattern viewed through the nail plate. The hyponychium is a short segment of skin lacking nail cover; it begins at the distal nail bed and terminates at the distal groove. Damage to specific regions of the nail unit will result in unique nail findings ( Table 25.1 ).

Nail Biopsy

Ungual biopsies are used to diagnose tumors, inflammatory disease, and infections. A punch or excisional biopsy technique is chosen, which provides a sufficient amount of tissue and produces a minimal amount of scarring. In practice these procedures are performed by some dermatologists and orthopedic hand surgeons. All of these techniques have been described.

Growth Rates

Nails grow continuously, but their growth rate decreases both with age and with poor circulation. Fingernails, which grow faster than toenails, grow at a rate of 0.5 to 2 mm per week. It takes approximately 5.5 months for a fingernail to grow from the matrix to the free edge and approximately 12 to 18 months for a toenail to be replaced. A reduction in the rate of matrix–cell division occurs in the presence of systemic diseases such as scarlet fever, causing thinning of the nail plate (Beau lines).

Psoriasis

Nail changes are characteristic of psoriasis (see p. 282 ), and the nails of psoriasis patients should be examined. These changes offer supporting evidence for the diagnosis of psoriasis when skin changes are equivocal or absent.

The incidence of nail involvement in psoriasis varies from 10% to 50%. Nail involvement usually occurs simultaneously with skin disease but may occur as an isolated finding. More than 50% of patients suffer from pain, and many are restricted in their daily activities.

Onycholysis

Psoriasis of the hyponychium results in the accumulation of yellow, scaly debris that elevates the nail plate. The debris is commonly mistaken for nail fungus infection. Psoriasis of the nail bed causes separation of the nail from the nail bed. Unlike the uniform separation caused by pressure on the tips of long nails, the nail detaches in an irregular manner ( Fig. 25.6 ). The nail plate turns yellow, simulating a fungal infection. Separation begins at the distal groove or under the nail plate and may involve several nails.

Nail Deformity

Extensive involvement of the nail matrix results in a nail losing its structural integrity, resulting in fragmentation and crumbling. Gross alteration of the nail plate surface and nail bed splinter hemorrhages are common ( Fig. 25.7 ).

Pitting

Pitting, or sharply defined ice pick–like depressions in the nail plate, is the most common finding ( Fig. 25.8A–B ). The number, distribution, patterns, and depth vary. Nail plate cells are shed in much the same way as psoriatic scale is shed, leaving a variable number of tiny, punched-out depressions on the nail plate surface. They emerge from under the cuticle and grow out with the nail. Many other cutaneous diseases may cause pitting (e.g., eczema, fungal infections, and alopecia areata), or it may occur as an isolated finding in a normal variation.

Triamcinolone Acetonide

Intralesional injection at monthly intervals into the matrix with triamcinolone acetonide (2.5 to 10 mg/mL) delivered with a 30-gauge needle is the standard treatment for psoriatic nail disease used by most dermatologists. A simplified protocol has been proposed. Triamcinolone acetonide (0.4 mL, 10 mg/mL) is injected, following ring block, at each of four periungual sites: two at the nail matrix and one in each lateral nail fold, directed medially towards the nail bed. This method is utilized to achieve delivery of the agent to both the nail matrix and the nail bed. If needed, a second set of injections is administered after 2 months. Subungual hyperkeratosis, ridging, and thickening respond well. Benefits are sustained for at least 9 months. Onycholysis and pitting are less responsive.

Calcipotriene (Calcipotriol)

Application of calcipotriene cream or ointment once daily every weeknight and clobetasol once daily every weekend for 6 months followed by clobetasol twice weekly for the second 6 months reduces subungual hyperkeratosis. Use of calcipotriene ointment twice daily for up to 5 months is less effective. Calcipotriene 0.005% and betamethasone dipropionate 0.064% solution is a combination that may be effective with once-daily application to nails and nail folds.

Tazarotene

Tazarotene 0.1% gel is applied each evening for up to 24 weeks to fingernails. Medication can be used under occlusion or nonoccluded. Tazarotene gel reduced onycholysis (in occluded and nonoccluded nails) and pitting (in occluded nails).

Biologic Drugs

TNF-α inhibitors (adalimumab, etanercept, infliximab, certolizumab and golimumab), ustekinumab, apremilast and tofacitinib have been utilized to treat refractory nail psoriasis.

Traditional systemic medications such as methotrexate, acitretin, and cyclosporine may be administered for nail psoriasis.

Acute Paronychia

The rapid onset of painful, bright red swelling of the proximal and lateral nail folds may occur spontaneously or may follow trauma or manipulation ( Figs. 25.10 and 25.11 ). Superficial infections present with an accumulation of purulent material behind the cuticle (see Fig. 25.11 ). The small abscess is drained by inserting a 23- or 21-gauge needle tip or similar instrument between the proximal nail fold and the nail plate and lifting the nail fold with the tip of the needle ( Fig. 25.12 ). Pain is abruptly relieved as the purulent material drains. There is no need for anesthesia or daily dressing. A diffuse, painful swelling suggests deeper infection, and cases that do not respond to antistaphylococcal antibiotics may require deep incision. Acute paronychia rarely evolves into chronic paronychia.

Chronic Paronychia

Chronic paronychia is not a yeast infection, but rather an inflammation of the proximal and lateral nail folds that may be colonized by Candida . Chronic paronychia evolves slowly and presents initially with tenderness and mild swelling around the proximal and lateral nail folds ( Fig. 25.13 ). Significant contact irritant exposure is a major cause. Individuals whose hands are repeatedly exposed to moisture (e.g., bakers, dishwashers, and dentists) are at greatest risk. Manipulation of the cuticle accelerates the process. Typically, many or all fingers are involved simultaneously. The cuticle separates from the nail plate, leaving the space between the proximal nail fold and the nail plate exposed to infection. Many organisms, both pathogens and contaminants, thrive in this warm, moist intertriginous space. The skin surrounding the nail becomes pale red, tender or painful, and swollen. Occasionally a small quantity of pus can be expressed from under the proximal nail fold. A culture of this material may grow Candida or Gram-positive and Gram-negative organisms. Candida is probably just a colonizer of the proximal nail fold rather than a direct cause of the disease. It disappears when the physiologic barrier is restored. The nail plate is not infected and maintains its integrity, although its surface becomes brown and rippled. There is no subungual thickening such as that present in some fungal infections. Proximal separation of the nail plate from the matrix area may occur as a consequence of nail matrix damage. The nail plate may sometimes present a green discoloration of its lateral margins as a result of Pseudomonas aeruginosa colonization. The process is chronic and responds very slowly to treatment. Psoriasis of the fingers may present in a similar form ( Fig. 25.14 ).

Drug-Induced Paronychia

The protease inhibitors lamivudine and indinavir, used to treat human immunodeficiency virus (HIV), have been reported to cause paronychia and ingrown toenails in about 4% of patients receiving these drugs. Pyogenic granuloma–like lesions, staphylococcal superinfection, onycholysis, and severe skin dryness may also be present. The nails of the great toes are usually affected. The lesions appear 2 to 12 months after starting treatment. Complete regression of skin manifestations occurs within 9 to 12 weeks after the drugs are withdrawn. Inhibition of endogenous proteases may explain the initial hypertrophy of the nail fold and the subsequent development of pyogenic granuloma–like lesions. Other drugs causing paronychia include: epidermal growth factor inhibitors, cytotoxic chemotherapy agents, and systemic retinoids.

Pseudomonas Infection

Repeated exposure to soap and water causes maceration of the hyponychium and softening of the nail plate. Separation of the nail plate (onycholysis) exposes a damp, macerated space between the nail plate and the nail bed, which is a fertile site for the growth of Pseudomonas . The nail plate assumes a green-black color ( Figs. 25.15 and 25.16 ). There is little discomfort or inflammation. This presentation may be confused with subungual hematoma (see Fig. 25.32 ), but the absence of pain with Pseudomonas infection establishes the diagnosis. Apply a few drops of a mixture of one part chlorine bleach/four parts water under the nail three times a day. Vinegar (acetic acid) and thymol 4% in alcohol may also be used.

Herpetic Whitlow

In the past, dentists and nurses were at risk of acquiring herpes simplex virus (HSV) infection of the fingertip. The risk has greatly diminished with the use of gloves. Young adults are typically affected by HSV-2. HSV-1 infection of the hand occurs in children as a result of autoinoculation following herpetic gingivostomatitis. The appearance and course of the disease resemble those at other body sites with grouped vesicles or ulcers on an erythematous base, except that there is extreme pain from the swollen fingertips ( Fig. 25.17 ). Lymphangitis and lymphadenitis, secondary to HSV infection of the hand, are possible complications, particularly with HSV-2 infection. Herpes simplex virus infection in acquired immunodeficiency syndrome (AIDS) patients is characterized by atypical presentations and unusual locations. Herpetic finger infections in these patients may rapidly progress to the complete destruction of nail structures. Viral culture or polymerase chain reaction confirms the diagnosis.

Tinea Versus Psoriasis

Differentiation of fungal infection from dystrophic changes resulting from psoriasis or other causes is difficult. Potassium hydroxide (KOH) preparations, culture, and, occasionally, nail-unit biopsy specimens are used. These tests are time-consuming and may yield false-negative results. Histologic examination of distal nail clipping specimens by routine histology and periodic acid – Schiff (PAS) staining is an accurate and simple method for differentiating onychomycosis from nail psoriasis ( Fig. 25.18 ). It is equal to culture and superior to KOH preparation in leading to the correct diagnosis of dermatophyte infection.

Laboratory Diagnosis

The diagnosis of fungal nail infection may be established with both a KOH examination and a culture, and occasionally with a nail biopsy. Confirm the species of fungus before starting oral antifungal treatment. When performing cultures, obtain crumbling debris from under several nails and at different parts (proximal and distal areas of infection) of the infected nail ( Fig. 25.19 ). Collect subungual debris from under the distal edge of the nail with a curette. Sample the nail surface with a curette or scrape it with a no. 15 scalpel blade ( Fig. 25.20 ). Fungi are found in the nail plate and in the cornified cells of the nail bed. Hyphae that are present in the nail plate may not be viable; therefore, sample the cornified cells of the nail bed if possible.