Tinea Unguum

Tinea unguum or onychomycosis is a common and relentlessly progressive fungal infection which may involve all or one of nail bed, nail matrix and nail bed.

• It may affect nails of the toes or fingers causing pain and disfigurement.
• Infection may have social, psychological and occupational consequences.
• It should not be regarded as trivial, particularly in the elderly or immunocompromised because of the complications that can occur.¹

Several subtypes are described several of which may occur in the same patient.
The terminology for the different subtypes is as follows:

• Distal and lateral subungal onychomycosis (DLSO). This is the most common variety and usually involves spread from plantar surface of the foot to the underside of the nail.
• White superficial onychomycosis (WSO). This is much less common and involves direct infection on the surface of the nail plate and then secondary infection of the deeper layers (nail plate and hyponychium).
• Proximal subungal onychomycosis (PSO). This is the most unusual subtype and involves spread from the cuticle through the nail to deeper layers.
• Endonyx (EO). This is a variant of DLSO with spread from skin directly to the nail plate.
• Candidal onychomycosis. This may result from primary infection in a number of ways or may result from colonisation of damaged nails, particularly nails affected by onycholysis.
• Total dystrophic onychomycosis. This involves a combination of all subtypes resulting in infection of the entire nail unit and scarring of the nail matrix.

• Age. Frequency increase with age, such that adults are more than 30 times more likely to be infected. About 90% of elderly patients become infected whereas less than 3% of those under 18 years of age have evidence of onychomycosis.
• Sex. Men are more likely to be infected than women although candidal infection is more common in women.
• Overall prevalence is between 3 and 13%.

History

• More patients are presenting for treatment.¹ Advertising directly to patients may be partly responsible for this.
• Patients do not usually present other than with complaints about appearence of nails.
• Discomfort with standing, walking or exercise may be a complaint occasionally.
• There may be clues about the cause:
  • Occupational factors
  • Immunosuppression.

Examination

Findings will depend on the type of nail involvement:

The differential diagnosis includes conditions which can cause thickening, discolouration of nails or onycholysis:

• Psoriasis
• Lichen planus
• Malignant melanoma
• Contact dermatitis and eczema
• Bacterial paronychia
• Thyroid nail disease
• Yellow nail syndrome
• Melanonychia
• Glomus tumours
• Subungal corns
• Squamous cell carcinoma
• Periungal warts
• Leuchonychia
• Bullous dermatoses
• Drugs including cytotoxics, antibiotics and retinoids

The diagnosis is usually made clinically but it is good practice to confirm the diagnosis before treatment.
When taking nail clippings and nail scrapings:

• The patient should have abstained from antifungal treatment for at least 2 weeks.
• The correct site (the affected site) should be sampled. In DLSO, for example, the specimen should be obtained by currettage of the nail bed as close to the cuticle as possible.
• Sufficient specimen with as much crumbly subungal material as possible should be sent for culture.

• Nail clippings and subungal scrapings:
  • Direct microscopy. Part of the sample can be soaked in 20% potassium hydroxide solution (to dissolve keratin) and examined under the microscope for hyphae.
  • The rest can be sent for culture in the post. Accuracy is helped by selecting the correct site for sampling, the correct size (more than 3mm width) of sample and as much crumbly subungal matter as possible.
• Nail biopsy:
  • This is not routinely recommended.
  • It is usually done by specialist familiar with the technique (usually a 3-4 mm punch biopsy).
  • It is used when differential diagnoses such as psoriasis and other dermatoses are being considered.

This has improved in recent years with newer agents. Inappropriate use and inadequate duration of treatment are a problem.¹ Toenails take about 12 months to grow out and fingernails about 6 months. This should be borne in mind when considering treatment.

General considerations

• The British Association of Dermatologists recommends that treatment should not be instigated on clinical grounds alone.¹ In practice this means at least taking samples before commencing treatment.
• Successful eradication of the fungus may not render the nails normal (they may have been dystrophic prior to infection).
• Patients should have some understanding of the cost of treatment, the risks of treatment and the risk of recurrence after treatment.
• Topical and oral agents are available.

Topical antifungals

• These are generally less able to cure infection because they do not penetrate the affected nail plate.
• It has been suggested that they may be useful as an adjunct to oral treatment or as preventive treatment. However more evidence is needed before such an approach can be recommended.⁴
• They can be useful in SWO and very early DLSO (involving less than half of the distal nail plate in no more than 2 nails).
• Amorolfine nail lacquer is likely to be the most effective although there are few studies directly comparing agents.^{1 5 6}
• A new setaconazole nail patch has been reported on but there is insufficient evidence to recommend use over existing agents.⁷

Oral antifungals

• The new generation of antifungals, including itraconazole and terbinafine, have replaced the older treatments. They offer shorter duration of treatment and better cure rates. They also have fewer side effects.² They penetrate the nail plate better. Terbinafine may be most effective.²
• Ketoconazole and fluconazole are not licensed for use in onychomycosis.
• Use of itraconazole and terbinafine in 'pulsed' fashion has been advocated. This works because both these agents persist in the nail long after elimination from the plasma.^{1 2}
• Terbinafine is licensed at a dose of 250mg daily for 6 weeks (fingernails) and 12 weeks (toenails).
• Itraconazole is licensed at a dose of 200mg daily for 12 weeks contiuously or 400mg daily for 1 week per month (3 such courses for toenails and 2 for fingernails).
• Terbinafine appears to be superior to both continuuous and intermittent ('pulsed') itraconazole.¹

Surgical treatment

• Mechanical and chemical removal can be performed.
• This is usually reserved for use when oral agents fail.¹

Infection of surrounding soft tissues with bacteria produces the most significant complications. These include cellulitis, osteomyelitis and tissue necrosis. Complications are most likely in diabetic patients.²

With correct diagnosis and treatment the prognosis is now good. Mycologic cure rates are relatively low at around 40% with typical clinical cure rates (nail looks normal) of around 75%.²

Patients should be educated about footwear, communal bathing and showering. Prompt treatment of tinea pedis also helps prevent onychomycosis.