Tinea unguium

Onychomycosis or invasion of the nail plates by species of dermatophytes (mostly Trichophyton rubrum) is one of the most common dermatological conditions (Figure 12.9). It is very rare in children but increases with age with toenails more commonly affected than finger nails. It is often associated with existing fungal skin infections, e.g. tinea pedis. Although sometimes considered to be a trivial cosmetic problem, it is relentlessly progressive and in the elderly can give rise to complications such as cellulitis and in those with diabetes or peripheral vascular disease can further compromise the limb. It can affect choice of footwear and mobility. It is therefore not surprising that it gives rise to many medical consultations and absence from work (Roberts et al., 2003).

It is clinically classified as (Hay and Moore, 2004):

1. Distal and lateral subungual onychomycosis (DLSO): This is the most common and nearly always due to dermatophyte infection. It often starts with a streak or patch of discoloration, white or yellow at the free edge of the nail plate, often near the lateral nail fold. It then spreads to the base of the nail and may become darker brown or black. The nail plate then thickens and lifts from the nail bed (onycholysis). Surrounding skin nearly always shows signs of tinea pedis. It commonly starts as one affected nail with other digits invaded later. There may be a marked variation in the degree of damage.
2. Superficial white onychomycosis (SWO): So called due to the ‘creamy’ white discolouration, distally this is less common than DLSO and affects the surface of the nail plate rather than the nail bed. The dorsal surface of the nail plate is eroded in well-circumscribed powdery white patches where the white material can be easily scraped away. Toenails are usually affected. Onycholysis is unusual.
3. Endonyx onychomycosis: The organism invades the nail plate from the top surface penetrating deep into the nail plate. There is white creamy discolouration. The nail plate is scarred with pits and lamellar splits. It is usually caused by dermatophytes which cause endothrix scalp infections, notably T. soudanense.
4. Proximal subungual onychomycosis (PSO): Fungi invade the nail bed and plate via the cuticle. The lanula (half moon) of the nail appear as patches of white or yellow discolouration. This is a rare variety of dermatophyte infection which is now more common particularly associated with immunosuppressed patients or those with diabetes or peripheral vascular disease. It is therefore important to think about intercurrent disease, especially HIV in these cases.
   
   

Differential diagnosis
The changes of the nail plate and bed can be mimicked by psoriasis, although fine pitting of the nail plate is never seen in fungal infections. Irregular buckling of the nail can be seen in eczema and in lichen planus there may be a ridged or dysplastic nail. Candida can cause paronychia of the nail where there is a tender area of infection where the nail and skin meet at the side or the base of a finger or toenail. However, this usually affects the nail plate proximally and laterally while the free edge is often spared initially. Ringworm of the finger nails is rarely symmetrical and it is common to find the nails of only one hand affected.

Management
This is not a trivial problem and affects many patients’ quality of life, functional activity and general well-being. On the grounds of complications, there is a real need to treat. Toenails can take 12 months to grow out and 70–80% cure rates can be expected with fingernails taking 6 months with a cure rate of 80–90% (Roberts et al., 2003). It is therefore vital that patients understand the nature of the disease and how it is spread along with an acceptance of the longterm nature and slow clinical improvement of antifungal treatments.

1. Careful clinical examination of the skin of the feet and of the palms is essential.
2. Treatment should not be started on clinical grounds alone because although 50% of nail dystrophies are due to fungal infection it is not always possible to identify these. A nail sample and clippings should be sent for mycological examination (Box 12.5). The sample needs to be from nail tissue where active disease is present which may mean paring down the nail with a scalpel and clippers to access the nail bed and debris in the middle of the suspected area of infection (Buchanan, 2006). Sampling white superficial nail infection involves scraping the upper surfaces of the nails with a curette or scalpel.
3. Evidence for the effective use of topical therapies to treat dermatophyte nail infections is limited (Crawford and Hollis, 2007) and systemic treatments are usually used. These include Terbinafine, Itraconazole, Griseofulvin.
4. Proper early treatment of tinea pedis and tinea manum (ringworm of the hand) would almost certainly reduce the prevalence of tine unguium (Hay and Moore, 2004). Candida species can be treated topically with an imidazole lotion or cream twice daily to the nail fold or oral Itraconazole for 14 days.
5. Early diagnosis and treatment is the most effective way to manage onychomycosis (Buchanan, 2006), so patient and carer education is fundamental.
6. Effective treatment of concomitant tinea infections of the skin, e.g. tinea pedis, to try and prevent ongoing nail involvement and infection is very important.
7. Patients also need practical advice on foot and nail care especially if they are high risk, e.g. elderly, those with psoriasis, diabetes, peripheral vascular disease or immunocompromised.
8. Advice should cover a good foot care regime encompassing:
   • Daily washing with warm (not hot) water and mild soap or soap substitute;
   • Careful drying, especially between toe webs;
   • Moisturising of dry, scaly skin on feet and heels with emollient, although this should be avoided between toes;
   • Avoiding the use of dusting powder between toes;
   • Socks, tights and shoes should fit well and socks and tights should be changed every day;
   • Daily checking for any redness, itching or swelling of skin between and around toes and any changes in colour, shape, thickness or smoothness of nails;
   • Cutting toe nails straight across in line with toe shape and avoiding cutting close to corners of nails;
   • Seeking advice for treatment of corns and calluses;
   • Prompt advice if fungal infection is suspected;
   • Possible referral to a podiatrist.
   
   

Box 12.5 Nail clipping sample Identify the active edge of the nail; Clip carefully and catch the keratin pieces in the black filter paper container.     Source: RCN/BDNG (2008).