SECTION 1: EPIDEMIOLOGY AND AETIOLOGY
This article describes the three most common types of nail changes to present to primary and secondary care: fungal nail disease, onycholysis and digital myxoid cysts.
Although these are relatively benign conditions, it is important to be aware of melanoma of the nail and to be able to differentiate this from benign melanonychia.
|Nail plate Permanent keratinised product of the nail matrix, grows throughout life|
|Nail matrix Extends approximately 6mm under the proximal nail fold; distal portion visible as white semicircular lunula. Ventral aspect of proximal nail fold encompasses a lower portion (matrix), and an upper portion (eponychium)|
|Nail bed Vascular bed on which nail rests. Extends from lunula to hyponychium; firmly attached to nail plate|
|Lateral nail folds Cutaneous, provide lateral borders to nail|
|Proximal nail fold Cutaneous, proximal nail border continuous with cuticle; under surface becomes dorsal aspect of nail plate|
|Growth Fingernails grow on average 0.1mm per day (3mm per month). Toenails take six to 12 months to grow fully|
Fungal nail disease
The mean prevalence of fungal nail infection (onychomycosis) is 4.3%.1 It is caused by infection with dermatophytes or by non-dermatophyte moulds and yeasts. Ninety per cent of cases are related to the dermatophyte Trichophyton rubrum.2The most common non-dermatophyte cause is Candida albicans.
Predisposing factors include diabetes mellitus, older age, genetic factors, psoriasis, immunodeficiency, smoking, peripheral vascular disease, physical activity and wet work.
Figure 1: Significant onycholysis on long, manicured nails (Photograph: Medical Illustration, NHS Fife)
Onycholysis can be classified as primary/idiopathic and secondary. Primary onycholysis is commonly seen in women who take great care over their nails. Significant onycholysis is seen on a background of long, manicured nails (figure 1). Active cleaning, often with sharp instruments, increases the onycholysis. Box 1 outlines the causes of secondary onycholysis.
|BOX 1: CAUSES OF SECONDARY ONYCHOLYSIS|
|Psoriasis, lichen planus, alopecia areata, bullous diseases|
|Tetracyclines, doxycycline, psoralens and fluoroquinolones can induce photo-onycholysis secondary to a phototoxic reaction on UV exposure|
|Partial hereditary onycholysis, congenital pachyonychia, ectodermal dysplasia|
|Amyloidosis, multiple myeloma, anaemia, bronchiectasis, yellow nail syndrome, lung cancer, diabetes mellitus, erythropoietic porphyria, thyroid disease, poor circulation, lupus erythematosus, scleroderma|
|Pregnancy, physical and chemical agents, trauma|
Melanonychia ('black nail') can be diffuse or linear and single or multiple. Melanocytes are present in the nail matrix, but not in the nail bed. If active, they can cause a longitudinal brown-black band, longitudinal melanonychia. The more proximal their origin, the more superficial the melanin in the nail plate.
Linear melanonychia may result from normal or abnormal melanocytes in the nail matrix. Abnormal melanocytes give rise to a subungual melanoma. Benign linear melanonychia is common in those with darkly pigmented skin, and in Japanese and Hispanic people.
Digital myxoid cysts
Digital myxoid cysts (myxoid pseudocysts or mucoid cysts), are benign tumours of the digit, commonly located at the distal interphalangeal joint or in the proximal nail fold. This is the most common ungual tumour. Myxoid cysts are thought to be a distal interphalangeal joint ganglion.
SECTION 2: DIAGNOSIS
Fungal nail disease
There are five main types of onychomycosis:
- Distal and lateral subungual onychomycosis Hyperkeratosis of under surface of distal nail plate and bed, onycholysis, dyschromias. Most common causative organism is T rubrum.
- Superficial white onychomycosis Superficial nail plate involved, most common in children. Most common causative organisms are T mentagrophytes and Aspergillus species.
- Proximal subungual onychomycosis Infection of proximal nail bed and nail plate, distal portion normal. Characteristically seen in immunocompromised patients. Most common causative organism is T rubrum.
- Endonyx onychomycosis Involves nail plate but not nail bed. Milky appearance, no subungual hyperkeratosis or onycholysis. Most common causative organism is T soudanense.
- Candidal onychomycosis May present as chronic paronychia with secondary nail dystrophy, distal nail infection, chronic mucocutaneous candidiasis or secondary candidosis. Typically found in those with chronic candidiasis or who carry out wet work.
Laboratory confirmation of a clinical diagnosis should be obtained before starting treatment. Microscopy and culture can take two to six weeks.3
The site should be cleaned with 70% ethanol before sample collection. Nail clippers can be used to obtain clippings from the nail plate and a scalpel blade to take scrapings from subungual hyperkeratosis.
For proximal subungual onychomycosis, a blade is used to pare away the healthy nail plate and take infected material from the nail plate closest to the lunula. Culture should be repeated if clinical suspicion is high and the first culture is negative – false negative rates can be up to 30%.3
Distal or distal lateral detachment of the nail plate from its bed, onycholysis begins laterally and proceeds proximally. When separation begins proximally, it is called onychomadesis. Women are predominantly affected.
Onycholysis creates a subungual space that gathers dirt and debris. Water accumulates and can predispose to secondary infection by bacteria and yeasts. Pseudomonas infection is common, with pain and green discoloration of the nail.
Distinguishing between subungual melanoma and linear melanonychia is difficult. The most common cause of a pigmented nail lesion is a subungual haematoma, which is easily distinguished from linear melanonychia because it usually migrates distally and its proximal margin is gently curved in one transverse axis.
There are a number of signs that should alert the clinician to a subungual melanoma (see box 2). If there is any suspicion of a subungual melanoma, a diagnostic biopsy must be taken from the nail matrix.
|BOX 2: RED FLAGS FOR SUBUNGUAL MELANOMA|
|Periungual spread of pigment to proximal and lateral nail folds and tip of a single digit (Hutchinson's sign)|
|Partial or total destruction of nail plate|
|Single digit involved|
|Develops suddenly in a previously normal nail plate|
|Distal narrowing of pigmented band, indicating lesion is originating proximally. Distal widening of band would indicate a benign cause|
|Medial part of lesion is dark, lateral parts clearer and blurred|
Digital myxoid cysts
Myxoid cysts are solitary or, rarely, multiple, skin-coloured/translucent, dome-shaped nodules approximately 5mm in diameter. They can be superficial, located near the proximal nail fold, or deep, located on the dorsum of the finger near the distal interphalangeal joint.
They contain a clear gelatinous/mucoid fluid, which may escape spontaneously or following trauma. When the cyst is situated on the proximal nail fold, it can result in nail plate changes secondary to pressure on the germinal matrix. This results in the formation of a longitudinal groove in the nail plate.
A cyst at the proximal nail fold may exude its contents into the cul-de-sac beneath the nail fold (figure 2). A rare variant is located beneath the nail matrix, producing convex distortion of the matrix and transverse overcurvature of the nail plate. Clinical features are most useful in diagnosis. Sterile puncture of the cyst, to demonstrate its mucoid contents, is useful to confirm clinical suspicion. Radiological examinations are unnecessary.
Figure 2: Digital myxoid cyst at the proximal nail fold (Photograph: Medical Illustration, NHS Fife)
SECTION 3: MANAGEMENT
Fungal nail disease
Topical treatments are not often effective because of lack of penetration through the dorsal plate. Monotherapy with topical antifungals can be used for superficial white onychomycosis and early distal and lateral subungual onychomycosis. Children's nails may respond to topical treatment because they are thinner.
The most common topical treatment is amorolfine 5% nail lacquer, applied once or twice weekly for six to 12 months. Ticonazole 28% nail solution is also available, which should be applied for six to 12 months.
The mainstay of treatment is systemic antifungals, although mycological cure rates are low, at only 30%.4 Terbinafine anditraconazole are the two main systemics indicated for treatment of onychomycosis (see box 3). Terbinafine is considered as first line because it results in higher cure rates and has fewer drug interactions.
After three months of treatment, most toenails still look abnormal. However, if therapy has been successful, normal nail will be seen emerging proximal to the dystrophic nail.
|BOX 3: TREATMENT OF ONYCHOMYCOSIS|
|250mg per day, six weeks fingernails, 12-16 weeks toenails|
|Contraindications liver disease, breastfeeding, pregnancy; monitor LFTs|
|200mg per day, six weeks fingernails, 12 weeks toenails OR|
|400mg per day for one week a month (pulse), with two pulses for fingernails, and three pulses for toenails|
|Consider as first-line agent for Candida species|
|Contraindications liver disease, congestive heart failure, concomitant benzodiazepines, statins, quinidines, pimozide, pregnancy, breastfeeding|
|The only licensed option for children. However, terbinafine is considered as the first-line treatment in children because of enhanced efficacy and shorter treatment duration4|
|Can be used as a third-line agent|
Treatment of onycholysis depends on the cause – eliminating and treating the cause is the best treatment. Nails should be cut back to the point of onycholysis, then a topical antifungal/antibacterial (such as a combination of clobetasone,nystatin and oxytetracycline) should be applied. The nails should be kept short, and trauma and prolonged contact with water avoided. Nails should be allowed to grow out and the patient should be educated not to clean underneath the nails.
If the clinical diagnosis is benign linear melanonychia, appropriate management would include a photograph for monitoring and follow-up by patient self-examination and in some cases, physician review.
If there is any suspicion of subungual melanoma, an urgent diagnostic biopsy must be taken from the nail matrix.
Digital myxoid cysts
There is no gold standard treatment option for digital myxoid cysts, but various treatment modalities are available (see box 4).
|BOX 4: TREATMENT FOR DIGITAL MYXOID CYSTS|
|Conservative – no treatment if asymptomatic|
|Intralesional steroid injection|
|Cryotherapy, two freeze/thaw cycles of 30 seconds|
|Injection of sclerosant after evacuation of myxoid fluid (0.25% polidocanol)|
|Excision of cyst and removal of osteophytes at distal interphalangeal joint|
- Dr Megan Mowbray is a consultant dermatologist at Queen Margaret Hospital, Dunfermline
- Sigurgeirsson B, Baran R. The prevalence of onychomycosis in the global population: a literature study. J Eur Acad Dermatol Venereol 2013; DOI: 10.1111/jdv.12323
- Summerbell RC, Kane J, Krajden S. Onychomycosis, tinea pedis and tinea manuum caused by non-dermatophytic filamentous fungi. Mycoses 1989; 32: 609-19.
- Hay R. Literature review. Onychomycosis. J Eur Acad Dermatol Venereol 2005; 19(Suppl 1): 1-7.
- Ameen M, Lear JT, Madan V et al. British Association of Dermatologists’ guidelines for the management of onychomycosis 2013; in press.
These action points can provide further CPD on this topic: