Fungal Nail Infections

Synonyms: Onychomycosis, OM, tinea unguium.

Various fungi may infect the nails of the hands or feet, and can affect any part of the nail from the nail bed, to the nail matrix and plate. Its most common consequence is a poor cosmetic appearance of the affected nail(s), but the condition may also have functional effects and cause discomfort, pain, frank disfigurement, limitation of mobility or inability to carry out certain jobs. The condition may also have adverse psychosocial and emotional effects (for instance, a reluctance to bare the feet in public, to use public baths, to take part in sport where there are communal changing facilities).¹ There are several patterns of presentation and infecting organisms.

This is one of the commonest dermatological conditions in the UK. Questionnaire surveys suggest a background prevalence of 2.71% of the population. Mycologically-controlled surveys in Finland and The United States indicate a prevalence of 7–10%. The toenails are affected in about 80% of cases of onychomycosis.² The incidence of new cases of onychomycosis appears to be rising due to the increasing prevalence of diabetes in the population, more frequent incidence of immunosuppression and an ageing population.¹

Risk factors

• Age – adults are ~30 times more likely than children to suffer the condition (affects 2.6% of children younger than 18 years, but as many as 90% of people older than 70 years).¹
• Immunosuppression – illness or medications that suppress immune responses greatly increase the likelihood of suffering onychomycosis.
• Diabetes mellitus – it can affect up to 30% of diabetic patients³
• Cutaneous fungal infection – around 30% will also have onychomycosis¹
• Warm, humid climate
• Participation in athletic/sporting activities
• Prior trauma to nail
• Regular communal bathing
• Occlusive footwear, e.g. rubberised plimsolls for maritime recreation
• Peripheral vascular disease

• Dermatophytes: Trichophyton rubrum or T. mentagrophytes causes over 90% of cases⁴, with T. rubrum being responsible for about 70% of the total.¹ Other organisms in this group include Epidermophyton sp. and Microsporum sp.
• Yeasts: Cause ~8% of total infections; particularly Candida albicans in the UK and Malassezia furfur in tropical climes.
• Non-dermatophyte moulds: Cause about 2% of total infections, e.g. Scopulariopsis brevicaulis.

• Distal and lateral subungual onychomycosis (DLSO):
  • Vast majority of cases of onychomycosis
  • Nearly always caused by dermatophytes
  • Affects hyponychium (epithelium of nail bed) often at the lateral edges initially
  • Spreads proximally along nail bed causing creamy/buff discolouration, subungual hyperkeratosis and onycholysis
  • Nail plate not affected initially but may become so in time
  • May be confined to one side of nail or spread sideways to involve whole nail bed
  • Relentless progression until it reaches posterior nail fold
  • Nail plate becomes friable and may disintegrate, particularly after trauma
  • Surrounding skin nearly always affected by tinea pedis, if careful observation carried out
  • Fingernail DLSO has similar appearance although nail thickening less common; toenail infection usually precedes it.

• Superficial white onychomycosis (SWO):
  • Less common than DLSO
  • Usually due to dermatophyte infection with T. mentagrophytes
  • Affects surface of the nail plate rather than nail bed
  • White rather than creamy discolouration
  • Notably flaky surface on nail plate
  • Onycholysis not usually a feature
  • Concurrent tinea pedis less common than in DLSO

• Proximal subungual onychomycosis (PSO):
  • Uncommon variety often found in immunocompromised, e.g. HIV infection
  • May also affect diabetic/peripheral vascular disease patients
  • Usually due to dermatophyte infection
  • Tinea pedis usually co-exists
  • Leukonychia in the proximal nail fold, can extend to deeper layers of the nail
  • Nail plate becomes white proximally and remains normal distally

• Candidal onychomycosis:
  • Causes chronic paronychia with secondary nail dystrophy
  • May affect distal nail alone without paronychial involvement (usually in cases of Raynaud's phenomenon or peripheral vascular disease)
  • Usually affects fingernails (without toenail involvement) in those whose occupations cause them to have constantly wet or allergen-irritated hands
  • Cuticular detachment and signs of infection and inflammation in the nail matrix may be observed
  • May complicate chronic mucocutaneous candidiasis or as a secondary infection due to other causes of nail disease, e.g. psoriasis.

• Total dystrophic onychomycosis:
  • Represents long-standing, severe, end-stage disease progressing from all of the above clinical patterns
  • Complete destruction of the nail plate is observed

• Irritant contact dermatitis
• Allergic contact dermatitis
• Lichen planus
• Subungual melanoma
• Psoriatic nail disease
• Bacterial paronychia, e.g. Pseudomonas infection
• Keratosis follicularis (Darier's disease)
• Idiosyncratic drug reaction (esp. tetracyclines, quinolones, psoralens)
• Paronychia congenita
• Yellow nail syndrome
• Nail-patella syndrome
• Thyroid disease
• Periodic shedding of nails

• Nail material should be sent for microscopy in 20% KOH solution to confirm fungal infection, and culture to determine the species
• Results of microscopy should be interpreted with caution as fungal organisms can exist as saprophytes, rather than as an invasive infection
• Subungual material from the most proximal part of the infection will give the highest yield as this is where the maximal concentration of hyphae is found
• In DLSO use a small dental scraper or similar instrument to obtain a specimen from beneath the nail plate
• In onycholytic nails cut them back to the most proximal point that can be attained and take a subungual sample and nail-bed sample
• Send the lab as much material as possible
• In SWO use a scalpel to scrape friable material off the surface of the nail
• in PSO use a scalpel blade to scrape away material from the proximal nail fold or perform punch biopsy to include material from nail bed
• Nail histology is not usually necessary unless there is reason to suspect another cause of nail pathology such as psoriasis
• Culture of Candida is not unusual in cases of psoriasis but does not necessarily indicate infection.

• Diabetes mellitus
• Any cause of immunocompromise
• Raynaud's phenomenon
• Peripheral vascular disease
• Tinea pedis
• Occupational dermatitis of hands
• Chronic mucocutaneous candidiasis
• Psoriasis
• Nail trauma

Traditionally there has been a reluctance to treat fungal nail infection as it has been seen as a trivial cosmetic problem. Current thinking is that anyone who presents should be offered treatment as it is probably causing significant distress if it crosses the threshold of the consultation room. If the condition progresses it can cause significant morbidity and functional disturbance, particularly in the elderly. There is also a public health argument for treating it, to lessen the reservoir of fungal spores in communal bathing areas, through reduction in the number of sufferers.⁴

• Topical anti-fungal therapy:
  • Should be reserved for cases where there is an inability to tolerate systemic antifungals, or mild disease of the distal nail (affecting less than half the nail plate)⁴
  • Treatment should be given daily for 6 months to 1 year
  • Can be used in cases of SWO or early-DLSO where infection is confined to the distal edge of the nail
  • 5% amorolfine is effective and appears to be the best topical agent in terms of its ability to penetrate the nail matrix⁵
  • 28% tioconazole is less effective but can be used successfully⁶
  • 8% ciclopirox is an effective treatment but does not currently have a UK licence
  • Combining topical ciclopirox with oral terbinafine appears to be more effective than oral terbinafine alone⁷
  • Topical nail patches containing anti-fungal agents such as sertaconazole show promising results and may be useful future therapies.⁸

• Systemic anti-fungal therapy:⁴
  • Griseofulvin may be used in adults and children. It is not expensive and there is a long experience of its use. It requires long duration of treatment (at least 6 months) and has low cure and high relapse rates. It interacts with warfarin, cyclosporin and the combined oral contraceptive pill. Nowadays it is rarely used except in the few cases of onychomycosis in children.
  • Terbinafine has high cure rates and is usually effective after 3 months of therapy. It is not licensed for use in children and there have been cases of severe idiosyncratic skin and hepatotoxic reactions. It interacts with rifampicin and cimetidine.
  • Itraconazole is highly active against Candida sp. but much less so against dermatophytes. It can be given in a pulsed rather than continuous regimen (1 week on, 3 off). It can cause hepatotoxicity and LFTs should be checked for treatment lasting longer than a month. It is contraindicated in pregnancy and not licensed for use in children. It interacts with a wide variety of commonly used pharmaceutical agents including warfarin, antihistamines, antipsychotics, digoxin, H2-antagonists, some statins and phenytoin.
  • Fluconazole may be a useful systemic agent but is not currently licensed for this indication

• Surgery:
  • Nail avulsion, removal of nail plate, chemical treatments (e.g. 40–50% urea solution for very thickened nails) and matrixectomy may enhance the effectiveness of oral treatment. Topical, systemic and surgical treatments can be combined to reduce costs, reduce length of treatment and improve efficacy.¹

• Poor cosmetic appearance of hands/feet
• Disfigurement and total destruction of nail plate
• Paronychia
• Damage to diabetic feet
• Psychosocial problems due to embarrassment at cosmetic appearance
• Pain and limitation of function, particularly in older patients

Cure rates vary from study to study but seem to be around 35–50% for those on terbinafine, which so far has been the most successful agent with best long-term results. Fingernail infections usually have much higher cure rates in the region of 70%. Untreated, fungal nail disease is usually progressive, leading to gradual destruction of the nail plate. However, there may be cases that spontaneously remit that do not present to their doctor.

Primary prevention is not practised, except where there is a cause of immunocompromise, such as AIDS, where prophylactic therapy may be considered. Secondary prevention with topical terbinafine cream after cure with systemic terbinafine appears to be effective in reducing relapse rates.¹