The skin defines who we are and how we are perceived to be. It is on our appearance we are judged by others (Lawton 2000). One only has to see the amount of time and money invested in changing or enhancing our appearance to appreciate how important the skin and its appendages are. A common mistake of students when faced with a patient with widespread skin disease is to remain at a distance, avoiding any physical contact. Skin diseases are subconsciously often perceived as nasty, dirty or infectious.

As a practitioner, preconceptions need to be overcome if the patient is to be reassured that they are in the care of an empathetic, understanding professional. It should be remembered that the problems of the skin patient may be more than skin deep, even with conditions that are perceived by the practitioner to be trivial. Many patients with most common skin disorders, such as psoriasis and eczema, have a quality of life that is similar to the quality of life of patients with other chronic diseases such as rheumatoid arthritis, cancer and heart disease. Often, the extent of the skin disease is not correlated with the sufferer’s well-being (Jayaprakasam et al 2002) and many conditions may be aggravated by psychological stress, such as atopic dermatitis, psoriasis and lichen planus. It should also be borne in mind that often just acknowledgement and discussion of the wider problems with a patient, in a sensitive and empathetic manner, is an important aspect of the assessment.

The purpose of assessment

The assessment procedure is at the heart of the diagnostic and treatment process. From a patient’s perspective assessment is seen as the reaching of a diagnosis and arriving at a decision on the most suitable form of treatment, i.e. what it is and what can be done about it. Most patients’ fears regarding skin disease revolve around issues such as ‘Is it catching?’ and ‘Will it get better?’. All the information gathered during the assessment will help to inform and reassure the patient accordingly.

The difficulty is that, to the untrained eye, many skin diseases appear similar. The second challenge is deciding whether the skin disease is part of an underlying systemic condition; therefore, the importance of the whole assessment process cannot be overstressed.

Many underlying conditions may be reflected in the condition of the skin and nails. For example, clubbing of the nails is a feature often associated with smoking and lung disease. Recurrent ulceration and infection of the foot is a common diagnostic marker in diabetes mellitus. Recognising such features will improve the likelihood of a successful diagnosis and treatment plan.

How common is skin disease?

Reliable data are difficult to obtain but skin disorders are thought to affect around a quarter of the population, with only a small percentage seeking professional help. Typically, 10–20% of a general practitioner’s annual workload involves skin disorders (Office of Population Census and Surveys 1991–1992), and podiatrists also spend a significant amount of time treating skin conditions (e.g. hyperkeratosis, nail disorders and wounds). The most common disorders that affect the lower limb (Gawkrodger 2002) are:

• fungal and other skin infections

• dermatitis/eczema

• psoriasis

• warts

• tumours (benign and malignant).

Skin structure and function

The skin (or integument) is the largest organ system and covers around 1.8 m². The skin is much more than just an inert wrapping, it is a highly active organ that fulfils many functions (Table 8.1) which are determined by its structure. The skin comprises three layers: an epithelium (epidermis) and a connective tissue matrix (the dermis) firmly bound together at the dermo-epidermal junction (Fig. 8.1); below the dermis lies the subcutaneous (fat) layer.

Table 8.1 Functions of the skin

Function	Specific property
Barrier properties	Physical: thermal/mechanical/radiation Chemical: irritants/allergens/water loss Microbiological: infections/infestations
Sense organ	Touch/vibration/pressure/temperature Nociception
Other	Thermoregulation and assistance in maintaining blood pressure Vitamin D and cholesterol production

Figure 8.1 Normal skin (not to scale) showing epidermis and dermis and the skin appendages, excluding nail.

Across the whole body surface, there are considerable regional variations in the skin’s structure, which in turn dictates its specific properties. These local variations may then influence the microclimate and, therefore, the pattern of organisms. Such variation may also account for the typical distribution of skin disease.

Epidermis

The epidermis (Fig. 8.2) is an avascular structure, relying on the diffusion of materials across the dermo-epidermal junction for nutrients and waste disposal. It is principally composed of keratinocytes (corneocytes), which make up approximately 80% of the cells, as well as melanocytes, Merkel’s discs and Langerhans’ cells. Appendages of the epidermis include the nails, sweat glands and sebaceous glands (Fig. 8.1).

Figure 8.2 The epidermis.

The epidermis ranges in thickness from around 0.4 mm to 1.5 mm, depending on the anatomical location; it is divided into four layers.

Basal layer (stratum germinativum)

For the most part, the basal layer consists of a single, undulating layer of cuboidal keratinocytes. The cells within this layer are firmly attached to the dermo-epidermal junction (DEJ) by tonofilaments which arise from the cytoplasm of the cells linking into the hemidesmosomes anchored into the DEJ (Venning 2000). These mitotically active cells generate the cells of the more superficial layers of the epidermis.

Scattered throughout this layer are specialist cells known as melanocytes. In sun-exposed areas (e.g. the face) they may have a ratio of 1 in 4, whereas on unexposed areas such as the plantar surface of the foot their numbers may decrease to 1 in 30. These cells are well developed in the epidermis of humans as we have a relatively hairless integument. Melanocytes are dendritic cells which produce the pigment melanin in specialist organelles known as melanosomes. These melanin granules then pass along the dendritic processes of the cell and are distributed evenly to adjacent keratinocytes. The melanin forms a protective cap over the cell nucleus, its function being to limit the amount of harmful ultraviolet radiation reaching the DNA within the nucleus. In addition, melanin and its hormonal pathways has a wider role in modulating inflammation within the skin (Eves et al 2006). The amount of melanin produced across various races is roughly equal; however, in darker skins the melanin granules are much more dense and less susceptible to degradation as they ascend through the epidermis.

Merkel’s cells are specialised nerve endings of unknown origin, possibly a modified keratinocyte (McKee 1996) found in the basal layer. Their function is thought to be the perception of light touch. They are typically only found in specific regions of the skin, being numerous on the volar (pulp) surfaces of the fingers and toes, in the nail beds and the dorsum of the foot.

Dermo-epidermal junction

The dermo-epidermal junction (DEJ) is the point at which the dermis meets the epidermis. The DEJ is a basement membrane divided into a number of layers, crossed by a complex of filaments, keratins and proteins that form an anchoring surface between the dermis and epidermis. In areas of greater mechanical stress, to enhance adhesion the dermis makes regular finger-like folds into the overlying epidermis, known as dermal papillae. These are complemented by protrusions from the epidermis into the dermis, known as rete pegs or epidermal ridges. This undulation serves to increase the surface area of attachment and is a major feature of the plantar surface of the foot, where mechanical stresses can be high. Pathologically, the DEJ is the site of many pathologies and this can lead to loss of adhesion and the development of blistering diseases (e.g. epidermolysis bullosa, dermatitis herpetiformis).

Dermis

Below the dermo-epidermal junction lies the dermis. This consists essentially of dense fibroelastic connective tissues in a gel-like base (ground substance) which contains glycosaminoglycans. Collagen strands provide tensile strength, with elasticity afforded by interwoven elastic fibres that make this a pliable tissue. Accommodated within the dermis are the skin appendages, macrophages, fibroblasts and the neurovascular network.

The thin, upper layer or papillary dermis contains most of the blood and lymphatic vessels, whereas the less vascular, deep reticular layer, is much more dense with collagen and elastic fibres. Cells of the immune system, i.e. T lymphocytes and mast cells, are present in the dermis.

Subcutaneous layer

The dermis is separated from the fascia by the subcutaneous (fat) layer. This is a layer of fat cells rich in nerves, blood vessels and lymphatics. Its main function is to provide thermal insulation and physical protection. To this end, it is well developed across the plantar surface, particularly across the metatarsal heads and heels where it may be up to 18 mm thick. Attached to the underlying fascia, plantar fat is divided into vertical chambers by dividing fibrous septae, which act as an effective shock absorption system.

Blood supply and lymphatics

The main blood supply to the skin arises from a network (or plexus) of vessels located in the subcutaneous layer. At this lowest level, branches supply eccrine sweat glands located deep in the reticular dermis. Vessels ascend and fan out to form a second plexus in the mid-dermis. Arterioles from this level supply hair follicles and their associated structures. Other vessels ascend further to form a third plexus in the papillary dermis.

From the papillary plexus, single capillaries loop upwards into the dermal papillae. These tiny vessels loop and descend to drain into venules within the papillary plexus and then descend further into the deeper dermis, eventually reconnecting with the subcutaneous blood vessels. Within the foot, the sole contains the most densely organised network of capillaries in the skin (Pasyk et al 1989), which correlates well with the thickness of the overlying epidermis. It has no thermoregulatory role.

Lymph vessels are found throughout the dermis. Within the papillary dermis, highly distensible lymphatic end bulbs drain intercellular fluids and smaller particles. These empty into larger vessels, which descend to the lymphatics in the subcutaneous layer. Ryan (1995) suggests that their function is key to maintaining turgidity, which is vital to retain mechanical resilience in the skin, requiring a fine balance between supply and drainage, as dehydration and oedema can lead to a reduction in skin stiffness and deformation in the structure of collagen and elastic fibres.

Skin appendages

Hair follicles and sebaceous glands

Hair follicles and their associated sebaceous glands are found on the lower limb, sparing the plantar surface. Compared with sebaceous glands in other areas of the skin (i.e. face, chest), these glands are relatively inactive.

Sweat glands

Sweat glands exist in two forms. The larger apocrine glands are exclusively associated with the hair follicle in the groin and axillae, whereas the smaller eccrine gland is a simple coiled structure located in the reticular dermis with an opening directly onto the epidermis. Stimulated primarily by the sympathetic branch of the autonomic system, sweat glands are an important mechanism for thermoregulation, mainly above waist level (Ryan 1995). They are most numerous on the palms and soles. Under normal circumstances a small, steady flow of sweat is produced, which is thought to aid grip. This function is further enhanced on the palms and soles by the presence of dermatoglyphics. These skin creases, present at birth, are a result of the unique arrangement of collagen fibres in the dermis and are more prominent on the weightbearing surfaces of the foot (pulp of the toes, heel and metatarsal area) and palmar area (fingerprints). Not only do they act like the tread on a tyre in conjunction with the small amounts of sweat, but within these areas, there is a dense and highly organised neural network in the underlying dermis (Montagna 1960) which provides a rich tactile perception necessary to protect the integrity of the foot.

History and examination of the skin

Dermatological assessment consists of three parts:

• history taking

• clinical examination

• common investigations and tests.

It is often tempting when assessing the skin to leap straight to examination without resorting to the standard clinical practice of history taking followed by examination. Although this approach may give a correct diagnosis in experienced hands, often, to those new to dermatology, this will lead to an incorrect or incomplete conclusion. However, a brief initial examination may help to direct questioning for the history.

History taking

Ideally, conduct the consultation in a private environment, with sufficient time to allow the patient to talk freely. You should expect to spend most of the consultation listening, only using questions to direct the history. It is important to ask patients what they think is the cause of the problem, as they are often correct. Starting the consultation by asking: ‘How may I help you?’ or ‘Tell me about your problem’ is beneficial. It lets patients know that they may talk and that there is willingness to listen, thus setting them at ease. However, certain facts are necessary to make a diagnosis and, if these are not offered, they should be asked for directly.

Duration of the problem

The duration of a disease is essential to know. Whether the disease is constant, deteriorating or fluctuating or whether there are periods of relapse and remission is useful. Acute or self-limiting conditions are usually inflammatory or infective (i.e. fungal infections), whereas chronic or progressive symptoms may be an indication of a more serious disease. Stressful events may give a remitting and relapsing pattern, particularly with psoriasis, eczema and lichen planus.

Relieving or exacerbating factors

Ask the patient if anything helps the problem or makes it worse. Many conditions improve in sunlight, for example psoriasis, whereas others are made worse, for example lupus erythematosus.

Relationships to physical agents

Find out whether light, heat or cold plays a part in the problem. Is the problem associated with any particular activity? Has injury played a part in the problem? Has there been exposure to chemical or plant material?

Treatment

This is one of the most essential questions. Alongside their usual medications, often patients will have tried to treat the problem themselves and will have bought over-the-counter medications, preparations from health shops or perhaps borrowed a prescribed medication from a friend or family member. They may also have tried cosmetic preparations that they do not consider relevant. It is often helpful to ask them to bring in everything they put on the skin. In some instances the true appearance of the skin lesion may be altered or masked by previously applied medicaments. For example, a steroid cream applied to a fungal infection will dramatically increase the spread of the eruption.

Past medical history

It is important to elicit any history of skin diseases, in particular psoriasis, eczema and skin cancer; all these conditions are pertinent to the lower leg and foot. Other salient conditions include information regarding a history of allergy, through either occupation or domestic exposure (e.g. epoxy resins from work or Elastoplast at home). Internal medical conditions may also be relevant, as many may manifest themselves in the skin. For example, dermatitis herpetiformis is a blistering disorder that is commonly associated with coeliac disease, a gluten intolerance affecting the gut.

Occupation

Many occupations expose the skin to irritants and allergens. A patient may need to wear a particular garment or item of footwear as part of their job and that may be causing the problem. It may be that other members of the workforce are similarly affected. Outdoor workers or workers who are exposed to wet or cold will also have problems particular to them; for instance, skin cancer is higher in those with outdoor occupations.

Social history

It is useful to know who is at home with the patient as they may be able to help with the treatment. Alcohol consumption is relevant to a number of skin conditions, particularly psoriasis. Enquiries about smoking should be made when considering circulatory problems. Smoking can have significant effects on the skin and is associated with hypersensitive corns on the plantar surface.

Family history

A number of skin conditions run in families, for example palmoplantar keratoderma. Recessively inherited diseases may skip generations, so information is required about distant relations too.

Recognising the norm in the assessment of skin is essential. Normal variations are seen due to race and the normal ageing process. Any given population will include a significant range of skin colours. Lesions that appear red or brown on white skin, for example often appear black or purple on pigmented skin and mild redness may be masked completely. In addition, some conditions have a distinct racial predisposition (e.g. melanoma in Caucasians). However, across all races, normal skin will not be different from surrounding skin and will feel smooth.

As the skin ages, it appears more translucent with irregular pigmentation. Thinning of the skin occurs at all levels, including the subcutaneous layer, which may be evident on the plantar area of the foot. Natural turgidity and elasticity seen in younger individuals is lost. Pinching of the skin results in ‘tenting’, as the skin fails to return to its natural shape. As a result of decreased sweat and sebum production, the normal skin surface barrier is compromised and so is more prone to the effects of drying and irritation. A reduced immune response as the numbers of lymphocytes and Langerhans’ cells decrease, potentially leaving the skin more open to infection and malignant change. Also, any inflammation that occurs as a result of decreased immune surveillance tends to be dampened down; hence, signs of inflammation may seem less acute. With ageing, the nails may reduce their rate of growth and often become thicker and slightly yellow in colour.

Clinical examination

Clinical examination of the skin uses a variety of senses. Sight is obviously the most important, but touch and smell are also valuable. Many trainees unused to dermatological assessment will shy away from touching the skin. This is clearly a natural reaction, but must be overcome in order to assess the area fully. Observation is an important stage in examination and it is important to follow a particular pattern:

• General distribution (localised, widespread or regional)

• Individual lesion morphology

• Assessment of other structures

• Assessment of the nails

• Assessment of the sweat glands.

General distribution

When a widespread eruption is suspected, it is important to look and ask about all of the skin. Patients may often be reluctant to discuss other areas or simply not connect them to the current condition. For example, scalp psoriasis can mimic dandruff. A patient concerned with scaly plaques on the knees may not connect the two, particularly if they have had dandruff for some time. Many disorders have a typical pattern or predilection for specific sites, although it should be remembered that patterns could occasionally vary from the norm. Eczema has a common pattern – affecting the flexor surfaces of the arms and legs along with the face. Symmetry of the eruption should also be recorded as this usually denotes an endogenous condition. Table 8.2 gives examples of the distribution patterns of various dermatoses.

Table 8.2 Common patterns of skin disorders

Condition	Typical distribution pattern
Atopic eczema	Antecubital and popliteal fossa, face, neck, hands
Contact dermatitis	Hands, face, feet
Psoriasis	Extensor surfaces of knees and elbows, scalp, back, nails
Lichen planus	Flexor surfaces of wrist, ankles, oral cavity, genitalia
Erythema nodosum	Anterior surfaces of shins

Individual lesion morphology

Individual lesions should be assessed. A magnifying glass is useful along with good lighting. Initially it is important, if there is more than one lesion, to describe the arrangement (Fig. 8.3). This can include:

Figure 8.3 The various configurations of lesion patterns.

Figure 8.4 Psoriasis.

Note that some disorders may have several configurations. Koebner’s phenomenon is when skin lesions of a specific disease appear following trauma at a site which was previously unaffected. The edge of the lesion should also be inspected. Is it discrete or ill-defined? For example, psoriasis and fungal infections have much more marked, well-defined edges than eczema. Surface contour should also be noted (Fig. 8.5).

Figure 8.5 The different surface contours of lesions.

Colour

To interpret the skin colour of lesions, good lighting is essential, as temperature and dependency will modify appearances. Rashes or lesions that are pink, purple or red will be due to blood. If the blood is within vessels gentle pressure will whiten or blanch the lesions – this is erythema, and can be viewed best through a glass slide or tumbler. If it is not possible to blanch the lesion, this may be due to extravasation (loss of blood constituents into the skin) or pigmentation due to melanin.

Touch

It is possible to determine surface changes in texture and whether the skin disease relates only to the surface of the skin or whether it relates to the structures beneath. Light touch is required to perceive superficial changes (i.e. texture of a surface lesion), whereas progressively deeper pressure will reflect changes to the lower structures in the dermis and subcutaneous layers. Oedema feels flocculent under the fingers. Typical surface changes include a soft moist texture due to excessive sweating or a dry and roughened texture due to a lack of sweating, that is anhidrosis. Deeper lesions may be described as hard, nodular, mobile, soft, etc.

Odour

Skin odour is a neglected aspect of skin examination but is useful. Colonisations of pseudomonas, staphylococcus or diphtheroids have distinctive smells (microbiology may help to confirm this) as do odours associated with excessive sweating (bromhidrosis) and incontinence.

When examining individual lesions, clear descriptions using well-recognised terms are essential. This allows good communication between health professionals. In dermatology, there are many descriptive terms: some obvious, others less so. Familiarity with this terminology will ensure good inter-professional communication. Skin lesions can be classified as primary or secondary. Primary lesions arise due to the initial effects of a condition; secondary lesions evolve from or as a complication of primary lesions. The distinction between primary and secondary is not always clear; some lesions can be classed as primary or secondary (Tables 8.3, 8.4). Some of the more common terms used in assessing the surface of the skin are described below.

Table 8.3 Primary skin lesions

Term	Description and example
Erythema	Redness, often due to inflammatory response
Macule	Flat, differently coloured, e.g. freckles, vitiligo
Papule	Palpable, solid bump in skin, e.g. lichen planus
Nodule	Palpable, deeper mass than a papule, e.g. ganglion, rheumatoid nodule
Plaque	Elevated, disc-shaped area of skin over 1 cm in diameter, e.g. psoriasis
Tumour	Large mass over 2 cm in diameter, e.g. lipoma
Cyst	Subdermal, fluid-filled fibrous swelling, loosely attached to deeper structures, e.g. dermal cyst
Weal	Large oedematous bump, e.g. insect bite
Vesicle	Tiny, pinprick-sized collection of fluid, e.g. mycosis, pompholyx
Bulla	Serous fluid/blood-filled intraepidermal or dermoepidermal sac, e.g. bullous pemphigoid
Pustule	Vesicle or bulla filled with pus, e.g. acne, pustular psoriasis
Burrow	Short, linear mark in skin visible with magnifying lens, e.g. scabies
Ecchymosis	Large extravasation of blood into the tissues, i.e. bruising
Petechia	Pinhead-sized macule caused by blood seeping into skin
Telangiectasia	Permanently dilated small cutaneous blood vessels

Table 8.4 Secondary skin lesions

Term	Description and example
Scale	Flake of skin, e.g. mycosis, psoriasis
Crust	Scab, dried serous exudates, e.g. acute eczema
Excoriation	Scratch marks, e.g. pruritus
Fissure	Crack in dry or moist skin
Necrosis	Non-viable tissue
Ulcer	Loss of epidermis; may extend through the dermis to deeper tissue, e.g. venous ulcer
Scar	Fibrous tissue production post-healing
Keloid	Excessive production of fibrous tissue post-healing
Striae	Lines in skin that do not have normal skin tone, e.g. striae tensa in pregnancy, Cushing’s disease
Purpura	Purplish lesions which do not blanche under pressure, e.g. vitamin C deficiency
Urticaria	‘Nettle rash’, e.g. drug eruption, allergy, heat
Lichenification	Patchy ‘toughening’ of skin, e.g. chronic eczema
Haematoma	Blood-filled blister
Sinus	Channel that allows the escape of pus or fluid from tissues

Scaly

Normally the skin sheds skin cells individually or in small clumps. This is imperceptible to the eye. If the skin is weathered or diseased, skin shedding becomes abnormal, the clumps of skin become larger and appear as flakes or scales. These scales may be small, as in the dryness (xerosis) of atopic eczema, or large, as in ichthyosis. Scratching the surface of skin is helpful as it accentuates scaling and may help with diagnosis. Psoriasis will demonstrate pinpoint bleeding when scratched and the scaling will become more pronounced (Auspitz’s sign).

Crusting and exudation

When the skin is injured or infected, it bleeds, oozes serum or discharges pus. This is an exudate; it dries to form a crust, which is distinguished from scale by clinical appearance and history. While avoiding hurting the patient, try to remove the crust as this often obscures the true pathology. Crusting is a common feature in eczema.

Hyperkeratosis and lichenification

If keratin is abnormal, it forms thickened areas as shedding fails. These can be localised, appearing as horns on the skin and usually reflect a viral or neoplastic process. Sometimes the surface can be papillomatous (warty). The areas of thickening can be more diffuse, e.g. chronic plantar eczema or corns. Such areas are less flexible and will often crack, forming deep fissures. Lichenification is a reaction of the skin to chronic rubbing or scratching and involves the whole epidermis. The affected area of skin thickens and the skin markings become more pronounced. It is a common feature of atopic eczema and usually occurs on the flexures.

Excoriations, erosions and ulcers

Excoriation means scratch and is usually a feature of itching or, less commonly, pain. It may represent underlying skin pathology such as scabies or eczema or indicate disease elsewhere, e.g. renal or hepatic failure. Erosions are partial-thickness breaks in the surface of the skin caused by physical injury including excoriation or where blisters have broken. An ulcer is an area of full-thickness skin loss, usually covered by exudate or crust.

Atrophic

The surface of the skin is depressed and blood vessels are visible beneath. It may be due to atrophy of the epidermis or dermis. The skin is often pale and wrinkled.

Macules and patches

These are localised impalpable areas of colour change: macules are less than 1 cm in diameter and patches are greater than 1 cm.

Papules, plaques and nodules

A papule is any lesion less than 1 cm in diameter that rises above the surface of the skin. A nodule is larger than 1 cm in diameter, but otherwise similar to a papule, and usually due to pathology within the dermis. A plaque is a raised lesion that is wider than it is thick and often represents epidermal pathology.

Vesicles, bullae, pustules and abscesses

Small blisters less than 1 cm are called vesicles. Blisters larger than 1 cm are called bullae. Pus-filled vesicles or bullae are pustules, large pustules are abscesses.

Weal

These are transient papular or plaque-like swellings of the skin due to dermal oedema and frequently seen in urticaria.

Scars

These can be macules, papules or plaques and are a feature of repair following dermal injury. A glossary of terms can be found in Tables 8.3 and 8.4.

Assessment of other structures

When examining the skin, other structures such as the nails, hair and mucous membranes may add clues to the diagnosis. For example, lichen planus commonly causes lesions in the mouth; this may be an important finding in differentially diagnosing it from other conditions such as eczema and psoriasis. Palpation of the lymph nodes is important in patients with suspected skin malignancy.

Assessment of the nail

The nails should be inspected as part of the main dermatological assessment. The nail has evolved as a rigid structure to improve dexterity but in the foot the nail is purely a protective plate overlying the deeper structures and acting as a counter pressure to the volar tissues (Baran et al 2003). The nail unit (Fig. 8.6) is well provided with a rich neurovascular supply and, as a result, is sensitive to internal changes, often manifesting these subtle changes in the nail structure. External factors too, such as trauma, can modify nail shape. Therefore, a proper footwear assessment should be undertaken, to complete the clinical picture, when looking for reasons for changes in nail shape, colour, etc. A glossary of the main terms used to describe nail changes can be found in Table 8.5.

Figure 8.6 Structure and anatomy of the nail.

Table 8.5 Glossary of nail conditions

Condition	Definition
Onychauxis	Thickening of the nail plate, usually due to trauma
Onychogryphosis	Thickened nail with a distortion in the direction of growth
Onycholysis	Separation of the nail from the nail bed, distal to proximal
Onychomadesis	Separation of the nail from the nail bed, proximal to distal
Onychocryptosis	Ingrowing toe nail
Involution	An inward curvature of the lateral or medial edges of the nail plate, towards the nail bed
Splinter haemorrhage	Longitudinal, plum-coloured linear haemorrhages (around 2 mm in length) under the nail plate
Paronychia	Inflammation of the tissues surrounding the nails
Onychomycosis	Fungal infection of the nail plate
Chromonychia	Abnormal coloration of the nail tissue
Koilonychia	Transverse and longitudinal concave nail dystrophy which gives a spoon-shaped appearance
Clubbing	Increased longitudinal curvature of the nail plate with enlargement of the pulp of the digit
Beau’s lines	Transverse ridging of the nail plate seen as the result of a temporary cessation of nail growth

Key aspects of examination include assessment of the following factors.

Pattern of affected nails

It is important to always assess finger nails as well as toe nails and note any findings. Often finger nails may show changes more readily (i.e. clubbing). Where only one or two nails are affected, or one foot, local causes should be suspected, whereas nail changes in all digits in both feet and hands suggests a systemic or internal cause. On the foot, the length or the position of the toes may give clues to local nail abnormalities. Typically, the longest toe may show nail changes as a result of interaction with footwear.

Rate of nail growth

There is great variation between individuals in the rate of nail growth. The average rate for a finger nail is 0.1 mm/day (or 3 mm/month), whereas toe nails grow at a half to a third of this rate (Zaias 1980). Consequently, a normal finger nail will grow completely in about 6 months, whereas a toe nail will take 12–18 months. Such information is useful to determine the approximate time of events, for example the time of trauma to a nail, the likely clearance time of a haematoma. Most systemic disorders lead to a decline in the rate of nail growth but a few may have the opposite effect (psoriasis, hyperthyroidism, nail trauma and drugs).