Dermatology - 香港醫學組織聯會

VOL.15 NO.11 NOVEMBER 2010
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
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 Slower
Daytime Night
Summer Winter
Men Women
Young Old
Right hand (dominant) Left hand/non-dominant
Minor trauma/nail biting Denervation
Fingers Toes
Psoriasis Finger immobilisation
Thyrotoxicosis Yellow nail syndrome
Pregnancy 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
Medical Bulletin
Dr. William TANG
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
warts
Yellow Onycholysis
Hypertrophic Pterygium Blue-grey IGN*
*IGN = Ingrowing nail
Hypertrophic
proximal NF
Red
13