VOL.15 NO.11 NOVEMBER 2010

Medical Bulletin

Nail and Nail Disorders Dr. William TANG FRCP (Edin & Glasg), FHKAM (Med)

Honorary Clinical Associate Professor, Dermatology Research Centre, Faculty of Medicine, The Chinese University of Hong Kong

Dr. William TANG

The nail unit is a dynamic complex which forms an important part of the integument. This complex consists of the nail matrix (NM), nail bed (NB), hyponychium, nail fold (NF) and the nail plate (NP). Cells of the nail matrix, under the protection of the proximal nail fold mature and keratinised to form the NP. The NM contributes to the most portion of the NP while about 10-15% is produced by the NB. As the NP grows distally, the continued addition of keratinised material makes the NP increases in thickness while it lengthens distally. There are variations in the rate of growth between different nails such that the middle finger (longest digit) grows the fastest. Finger nails grow faster than toe nails. A finger nail grows about 1 cm in 3 months while a toe nail only grows about 1 cm in 9 months. Nail growth can be affected by many factors (Table 1). Table 1 : Some acquired factors affecting nail growth Faster Daytime Summer Men Young Right hand (dominant) Minor trauma/nail biting Fingers Psoriasis Thyrotoxicosis Pregnancy

Slower Night Winter Women Old Left hand/non-dominant Denervation Toes Finger immobilisation Yellow nail syndrome Fever

Clinical Examination of Nail When examining the nails, one should examine all 20 nails with the digits relaxed. Nail polish and lacquer should be removed. For a new consultation, it is better to advise the client in advance to avoid applying topical nail medicaments or cosmetics and to keep nail growing for sometime till slightly longer so that an accurate nail examination can be performed. The rest of the skin and mucous membranes and other systems should be examined for evidence of disease. Close examination of pigmented lesions and vasculature can be facilitated by the use of dermoscopy. Common investigations for nail diseases like swab for culture and sensitivity test, nail scraping and nail clipping are simple and easy to perform. A microscopic examination of the nail scraping can be done after the nail specimen has been treated with 30% potassium hydroxide. Clipped nail specimens should also be sent for fungal culture. However, when the specimens

harvested are minute in amount, it is better to send all for fungal culture as mycologic yield for onychomycosis is low. 2 A higher amount of nail specimen could be obtained by curettage. Drilling the proximal border of the diseased nail to obtain nail samples where live fungi could be more abundant has been reported to give a higher yield. 3 Considering the special anatomical structure of a nail in contrast to skin, investigations like plain X-rays for bone/joint abnormalities, ultrasound and MRI for soft tissue lesions should be made for accurate evaluation and confirmation of the clinical suspicion as deemed appropriate in collaboration with radiologists. The hard keratinous NP forms a natural physical barrier from a thorough clinical examination. In addition, it may also hinder delivery of topical therapy. Therefore, physicians would need reasonably good exploration skill in order to tackle the varied features seen in different nail disorders.

Normal Variants, Minor Ailments and Common Nail Disorders (Table 2, Table 3) The normal nail appearance varies among individuals. Common features include length and width variation. The size of the lunula also differs among different individuals. A variety of pathological abnormalities can affect the nails but sometimes they do occur in a much milder form in otherwise normal persons. When pits affect a normal person, they are much fewer in number and usually affect only one or two nails; punctate leukonychia occurs as white spots at one or two sites of the NP, possibly attributed to minor trauma and is not significant other than cosmetic nuisance. It is noted that striae leukonychia can sometimes be hereditary and a positive family history gives the clue. Small grooves can occur on the thumb nail due to a habit-tic. One or two splinter haemorrhages under the distal NP can also be trauma-related and very often not due to systemic diseases. Old people have fine longitudinal ridges producing mild NP roughness which is aged-related. Table 2 : A simple classification of nail abnormalities Surface Configuration Consistency Soft tissue Colour Others Pits Koilonychia Brittle Paronychia Leukonychia Myxoid cyst Grooves Clubbing Hard Ragged cuticle Brown Subungual exostosis Ridges Transverse Soft Splinter Black Tumours overcurvature haemorrhage Lines Atrophic Periungual Yellow Onycholysis warts Hypertrophic Pterygium Blue-grey IGN* Hypertrophic Red proximal NF *IGN = Ingrowing nail

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VOL.15 NO.11 NOVEMBER 2010

Medical Bulletin Table 3 : Common nail diseases seen in dermatological clinic Idiopathic Trachyonychia

Infection Onychomycosis

Onycholysis

Periungual wart

Irritant Chronic paronychia

Inflammatory Psoriatic onychopathy Lichen planus

*IGTN = Ingrowing toe nail

Onychomycosis Defined as a fungal infection of the nail. Represents up to 30% of diagnosed superficial fungal infections. Fungi include Trichophyton, Microsporum and Epidermophyton species. Yeasts and nondermatophytic moulds are also responsible for a minority of cases. There are four clinical types of onychomycosis: 1. Distal lateral subungual onychomycosis (DLSO): primarily involves the distal NB and the hyponychium, secondary involvement of the underside of the NP. Usually caused by T. rubrum. 2. Superficial white onychomycosis (SWO): is an invasion of NP on its surface. T. Mentagrophytes is a common pathogen. 3. Proximal subungual onychomycosis (PSO): involves the NP mainly from the proximal NF, caused by T. rubrum and more frequently affecting HIV-positive patients. 4. Candida onychomycosis: commonly affecting nails of hands. If seen in chronic mucocutaneous candidiasis, it may produce massive NB hyperkeratosis and destroys the nail. Whichever the clinical types, untreated onychomycosis rarely may deteriorate to total destruction of the nail plate (total dystrophic onychomycosis). Moulds account for a minority (