Skin disease



Skin disease


S.H. Ibbotson


R.S. Dawe



Clinical examination in skin disease


image



imageKey points in the history and examination in skin disease


It may be tempting to examine the skin before anything else. This is a mistake; take a history first, and then examine the skin and the rest of the patient.



History


History-taking should follow general principles:







imageTerms used to describe skin lesions



Lesion types





Other terms




• Abscess: a localised collection of pus in a cavity


• Atrophy: an area of thin, translucent skin caused by loss of epidermis, dermis or subcutaneous fat, e.g. secondary to excess topical corticosteroids (see Fig. 28.8, p. 1265)


• Burrow: a linear or curvilinear papule, caused by a burrowing scabies mite (see Fig. 28.25A, p. 1280)


• Comedone: a plug of keratin and sebum in a dilated pilosebaceous orifice


• Crust: dried exudate of blood or serous fluid (see Fig. 28.17, p. 1275)


• Erosion: an area of skin denuded by complete or partial loss of the epidermis


• Excoriation: a linear ulcer or erosion resulting from scratching


• Fissure: a slit-shaped deep ulcer, e.g. in irritant dermatitis of the hands


• Petechiae, purpura and ecchymosis: petechiae are pinhead-sized, flat macules of extravascular blood in the dermis; purpura are larger and may be palpable; ecchymosis (‘bruise’) is the term used to describe bleeding that involves deeper structures


• Scale: a flake arising from the stratum corneum. Any condition with a thickened stratum corneum, i.e. hyperkeratosis, can cause scaling. An immature thickened and cohesive stratum corneum, e.g. as in psoriasis or Bowen’s disease, gives characteristic optical and physical properties that cause a different scale from that due to a thickened, but otherwise normal, stratum corneum (see Fig. 28.11, p. 1271)


• Scar: replacement of normal structures by fibrous tissue at the site of an injury


• Sinus: a cavity or channel that permits the escape of pus or fluid


• Stria: a linear, atrophic, pink, purple or white band caused by connective tissue changes (see Fig. 28.8, p. 1265)


• Telangiectasia: visible dilatation of small cutaneous blood vessels (see Fig. 28.9A, p. 1270)


• Ulcer: an area from which the epidermis and at least the upper part of the dermis have been lost (see Fig. 28.7, p. 1263)


• Weal: an evanescent discrete area of dermal oedema, often centrally white due to masking of local blood supply by fluid; weals can be papules, macules, patches and plaques, and are the hallmark of urticaria (see Fig. 28.34, p. 1291)


Disease affecting the human skin is common, and is important because the absence of normal skin function, as well as sometimes being life-threatening, can severely impair quality of life. This may be exacerbated by the fact that people with skin disease may suffer the effects of stigma, on occasion stemming from others’ belief that skin changes are the result of contagious disease.


Skin diseases affect all ages and number more than two thousand. Assessment of the skin is valuable in the management of anyone presenting with any medical problem and, conversely, assessment of the other body systems is important when managing primarily skin disease. This chapter concentrates on those skin diseases seen most frequently and those that are important as components of general medical conditions affecting other organ systems along with the skin. Skin infections, including those related to the human immunodeficiency virus (HIV), are also discussed in Chapters 13, 14 and 15.



Functional anatomy and physiology


The skin covers just under 2 m2 in the average adult. The outer layer is the epidermis, a stratified squamous epithelium consisting mainly of keratinocytes. The epidermis is attached to, but separated from, the underlying dermis by the basement membrane. The dermis is less cellular and supports blood vessels, nerves and epidermal-derived appendages (hair follicles and sweat glands). Below it is the subcutis, consisting of adipose tissue.




Epidermis


On most sites, the epidermis is only 0.1–0.2 mm thick, except on the palms or soles where it can extend to several millimetres. Keratinocytes make up approximately 90% of epidermal cells (Fig. 28.1). The main proliferative compartment is the basal layer. Keratinocytes synthesise a range of structural proteins, such as keratins, loricrin and filaggrin (filament aggregating protein), that play key roles in maintaining normal cutaneous physiology. There are more than 50 types of keratin and their expression varies by body site, site within the epidermis and disease state. Mutations of certain keratin genes can result in blistering disorders (p. 1291) and ichthyosis (characterised by scale without major inflammation). As keratinocytes migrate from the basal layer, they differentiate, producing a variety of protein and lipid products. Keratinocytes undergo apoptosis in the granular layer before losing their nuclei and becoming the flattened corneocytes of the stratum corneum (keratin layer). The epidermis is a site of lipid production, and the ability of the stratum corneum to act as a hydrophobic barrier is the result of its ‘bricks and mortar’ design; dead corneocytes with highly cross-linked protein membranes (‘bricks’) lie within a metabolically active lipid layer synthesised by keratinocytes (‘mortar’). Terminal differentiation of keratinocytes relies on the keratin filaments being aggregated and this is, in part, mediated by filaggrin. Mutations of the filaggrin gene are found in icthyosis vulgaris, and occur in some patients with atopic eczema (p. 1283).



The skin is a barrier against physical stresses. Cell-to-cell attachments must be able to transmit and dissipate stress, a function performed by desmosomes. Diseases that affect desmosomes, such as pemphigus (p. 1294), result in blistering due to keratinocyte separation.


The remaining 10% of epidermal cells are:





Dermis


The dermis is vascular and supports the epidermis structurally and nutritionally. It varies in thickness from just over 1 mm on the inner forearm to 4 mm on the back. Fibroblasts are the predominant cells; others include mast cells, mononuclear phagocytes, T lymphocytes, dendritic cells, neurons and endothelial cells. The acellular part of the dermis consists mainly of fibres, including collagen I and III, elastin and reticulin, synthesised by fibroblasts. Support is provided by an amorphous ground substance (mostly glycosaminoglycans, hyaluronic acid and dermatan sulphate), whose production and catabolism are altered by hormonal changes and ultraviolet radiation (UVR). Based on the pattern of collagen fibrils, the superficial dermis is termed the ‘papillary dermis’, and the deeper, coarser part is the ‘reticular dermis’.



Epidermal appendages



Hair follicles

There are 3–5 million hair follicles, epidermal invaginations that develop during the second trimester. They occur throughout the skin, with the exception of palms, soles and parts of the genitalia (glabrous skin). The highest density of hair follicles is on the scalp (500–1000/cm2). Newborns are covered with fine ‘lanugo’ hairs, which are usually non-pigmented and lack a central medulla; these are subsequently replaced by vellus hair, which is similar but more likely to be pigmented. By contrast, scalp hair becomes terminal hair, which is thicker with a central medulla, is usually pigmented and grows longer. At puberty, vellus hairs in hormonally sensitive regions, such as the axillary and genital areas, become terminal.


Human hairs grow in a cycle with three phases: anagen (active hair growth), catagen (transitional phase) and telogen (resting phase). The duration of each phase varies by site. On the scalp, anagen lasts several years, catagen a few days and telogen around 3 months. The length of hair at different sites reflects the differing lengths of anagen.







Functions of the skin


The skin has many functions, all of which can be affected by disease (Box 28.1). Skin changes associated with ageing are shown in Box 28.2.





Investigations








Microbiology






Patch testing


Patch testing investigates delayed, cell-mediated, type IV hypersensitivity, which manifests as dermatitis. It is a provocation test with potential allergens (see Box 28.26, p. 1285) applied, at concentrations and in vehicles to minimise false positive and false negative reactions, under occlusion to the back for 48 hours before examination. When interpreting patch test readings, it is important to determine the clinical relevance of any allergic reactions before giving avoidance advice.


Photopatch testing is similar to patch testing, but investigates delayed hypersensitivity to an agent (usually a sunscreen or a non-steroidal anti-inflammatory (NSAID)) after the absorption of UVR. It involves applying substances in duplicate and irradiating one set with UVR (typically UVA, 5 J/cm2), with readings then conducted in a similar manner to patch testing.




Phototesting


Phototesting is important for assessing suspected photosensitivity. The mainstay investigation is monochromator phototesting, which involves exposing the patient’s back to increasing doses of irradiation using narrow wavebands across the solar spectrum and then assessing responses, using the minimal erythema dose (MED) at each waveband. This is the dose required to cause just perceptible skin reddening and is compared with values for the normal population. If a patient has reduced MEDs (i.e. develops erythema at lower doses than healthy subjects), this indicates abnormal photosensitivity. Thus, monochromator phototesting can be used to determine whether a patient is abnormally photosensitive, which wavebands are involved and how sensitive the patient is (p. 1260). Provocation testing can be performed with a broadband (usually UVA) source to induce rash at a test site (most useful for polymorphic light eruption) and can be helpful for diagnosis.


Patients who are referred for phototherapy will also usually undergo an MED test, in which they are exposed to a series of test doses of the light source that will be used therapeutically (often narrowband UVB), and the MED is determined 24 hours later (or 72–96 hours for the psoralen–ultraviolet A (PUVA) minimal phototoxic dose) (p. 1266). This allows treatment regimens to be individualised, based on a patient’s erythemal responses, and may detect abnormal photosensitivity.



Presenting problems in skin disease


The major presentations in dermatology are outlined below. Detail about the underlying disorders is mostly provided in the disease-specific sections later on.



Lumps – new or changing lesions


A ‘new or changed lesion’ is one of the key dermatology presentations. The challenge is to distinguish between benign and malignant disease (p. 1269). Detailed history-taking and examination are essential:



• Lesion: Is this new or has a pre-existing lesion changed? What is the nature of the change – is it in size, colour, shape or surface? Has change been rapid or slow? Are there other features – pain, itch, inflammation, bleeding or ulceration?


• Patient: What is the patient’s age? Are they fair-skinned and freckled? Has there been much sun exposure? Have they used sunbeds or lived in sunny climates? Have they used photoprotection?


• Site: Is it sun-exposed or covered? The scalp, face, upper limbs and back in men, and face, hands and lower legs in women, are the most chronically sun-exposed sites.


• Are there other similar lesions? These might include actinic keratoses (see Fig. 28.11, p. 1271) or basal cell papillomas (see Fig. 28.15, p. 1274).


• Morphology of the lesion: Tenderness, size, symmetry, regularity of border, colour, surface characteristics and the presence of features such as crust, scale and ulceration must be assessed. Stretching the skin and using a magnifying lens can be helpful, e.g. in detecting the raised, pearled edge of a basal cell carcinoma (p. 1270).


• Dermatoscopy: This can be used to detect the presence of abnormal vessels, such as in basal cell carcinoma or the characteristic keratin cysts in basal cell papillomas. It is invaluable for assessing pigmented and vascular lesions (Fig. 28.2).




Is it a melanocytic naevus or a malignant melanoma?


This is a common differential and one that it is critical to resolve correctly.



The ABCDE ‘rule’ is a guide to the characteristic features of melanoma (Box 28.3 and see Fig. 28.2), although, ideally, melanomas should be diagnosed before the diameter is greater than 0.5 cm. Loss of normal skin markings in a pigmented lesion may be suggestive of melanoma. Conversely, normal skin markings and fine hairs dispersed evenly over a lesion are reassuring but do not exclude melanoma. The Glasgow seven-point checklist is another useful guide:





Rashes – papulosquamous eruptions


A rash is the other common presentation in dermatology. The main categories of scaly rashes are listed in Box 28.4. Diagnosis can often be made on clinical grounds, although a biopsy may be required. Important aspects of the history are:




• Age at onset and duration of rash? For example, atopic eczema often starts in early childhood and psoriasis between 15 and 40 years, and both may be chronic. Infective or drug-induced rashes are more likely to be of short duration and the latter occur in relation to drug ingestion. Duration of individual lesions is also important, as, for example, in urticaria.


• Body site at onset and distribution? For example, flexural sites are involved in atopic eczema and extensor surfaces and scalp in psoriasis. Symmetry is often indicative of an endogenous disease, such as psoriasis, whereas asymmetry is more common with exogenous causes, such as contact dermatitis or infections like herpes zoster.


• Is it itchy? For example, eczema is usually extremely itchy and psoriasis less so.


• Was there a preceding illness or were systemic symptoms present? Examples include guttate psoriasis precipitated by a β-haemolytic streptococcal throat infection; almost all patients with infectious mononucleosis (p. 320) treated with amoxicillin will develop an erythematous maculopapular eruption; the rash of secondary syphilis follows a history of chancre at the site of inoculation; malaise and arthralgia are common in drug eruptions and vasculitis.


The morphology of the rash and the characteristics of individual lesions are important (see Box 28.4).



Blisters


There are a limited number of conditions that present with blisters (Box 28.5). Blistering occurs due to loss of cell adhesion within the epidermis or sub-epidermal region (see Fig. 28.1, p. 1253), and the clinical presentation depends on the site or level of blistering within the skin, which in turn reflects the underlying pathogenesis (p. 1291):




• Intact blisters are not often seen if the split is high in the epidermis (below the stratum corneum), as the blister roof is so fragile that it ruptures easily, leaving erosions (e.g. pemphigus foliaceus, staphylococcal scalded skin syndrome (see Fig. 28.18, p. 1276) and bullous impetigo).


• If the split is lower in the epidermis, then intact flaccid blisters and erosions may be seen (e.g. pemphigus vulgaris and toxic epidermal necrolysis (see Fig. 28.36, p. 1292)).


• If the split is sub-epidermal, then tense-roofed blisters occur (e.g. bullous pemphigoid (see Fig. 28.37, p. 1294), epidermolysis bullosa acquisita and porphyria cutanea tarda (see Fig. 28.47, p. 1302)).


• If there are foci of separation at different levels of the epidermis, as in a dermatitis (p. 1283), multilocular bullae (made up of coalescing vesicles) occur.


A history of onset, progression, mucosal involvement, drugs and systemic symptoms should be taken. Clinical assessment of the distribution, extent and morphology of the rash should then be made. The Nikolsky sign is useful: sliding pressure from a finger on normal-looking epidermis can dislodge the epidermis in conditions with intra-epidermal defects, such as pemphigus and toxic epidermal necrolysis.


A systematic approach to diagnosis is required:



Investigations and management are guided by the clinical presentation and differential diagnosis, and are described in this chapter under the specific diseases.



Itch (pruritus)


Itch is an unpleasant sensation that leads to scratching or rubbing. The terms ‘itch’ and ‘pruritus’ are synonymous; however, ‘pruritus’ is often used when itch is generalised. Itch can arise from primary cutaneous disease or from systemic disease, which may cause itch by central or peripheral mechanisms. Even when the mechanism is peripheral, there are not always signs of primary skin disease.


The nerve endings that signal itch are in the epidermis or near the dermo–epidermal junction. Transmission is by unmyelinated slow-conducting C fibres through the spinothalamic tract to the thalamus and then the cortex. There is an inhibitory relationship between pain and itch. Scratching either causes inhibition of itch receptors by stimulating ascending sensory pathways that inhibit itch at the spinal cord (Wall’s ‘gate’ mechanism), or interferes directly with cutaneous itch fibres by direct damage.


The mechanisms of itch in most systemic diseases remain unclear. The itch of kidney disease, for example, may be mediated by circulating endogenous opioids. The clinical observation that peritoneal dialysis helps reduce itch more frequently than haemodialysis is consistent with this, smaller molecules generally being dialysed more readily if the peritoneal membrane is used rather than a dialysis machine membrane.




Clinical assessment

Diagnosis is important and full assessment, through history, examination and, sometimes, investigations, is necessary. When a patient presents with generalised itch, it is important to determine whether skin changes are primary (a process in the skin causing itch) or secondary (skin changes caused by rubbing and scratching because of itch). Many common primary skin disorders are associated with itch (Box 28.6). If itch is not connected with primary skin disease, many causes should be considered (Box 28.7); these include liver diseases (mainly cholestatic diseases, such as primary biliary cirrhosis), malignancies (e.g. generalised itch may be the presenting feature of lymphoma), haematological conditions (e.g. generalised itch in chronic iron deficiency or water contact-provoked (aquagenic) intense itch in polycythaemia), endocrine diseases (including hypo- and hyperthyroidism), chronic kidney disease (in which severity of itch is not always clearly associated with plasma creatinine concentration) and psychogenic causes (such as in ‘delusions of infestation’). Pruritus is common in pregnancy and may be due to one of the pregnancy-specific dermatoses. Diagnosis is particularly important in pregnancy, as some disorders can be associated with increased fetal risk (Box 28.8).






Management

There are no consistently effective therapies to suppress itch, regardless of its cause but establishing the diagnosis is the first step. If a clear-cut diagnosis is not apparent, various non-specific approaches can be used for symptom control. It is important to re-assess the patient intermittently in order to avoid missing the diagnosis.


Approaches to symptomatic relief include sedation, often with H1 antagonist antihistamines; emollients; and counter-irritants (such as topical menthol-containing preparations). UVB phototherapy is useful in itch stemming from a variety of causes, although the only randomised controlled study evidence of its efficacy in generalised itch not caused by a skin disease is for the itch of chronic kidney disease. Other treatments include tricyclic antidepressants (probably through similar mechanisms to those involved when these drugs are used for chronic pain) and opiate antagonists. Itch can be severe and its effects on quality of life are not always appreciated.



Photosensitivity


Cutaneous photosensitivity is an abnormal response of the skin to ultraviolet (UVR) or visible radiation. The sun is the natural source but patients may also be exposed to artificial sources of UVR through the use of sunbeds and/or phototherapy (p. 1266). Chronic UVR exposure increases skin cancer risk and photoageing (p. 1254). Acute exposure can induce erythema (redness) as a normal response (Fig. 28.3). However, abnormal photosensitivity occurs when a patient reacts to lower doses than would normally cause a response, either with a heightened erythemal reaction or the development of a rash. Photoaggravated skin diseases are exacerbated by sunlight but not caused by it. The main photosensitive and photoaggravated diseases are listed in Box 28.9.



image28.9   The photosensitivity and photoaggravated diseases

























































Cause Condition Clinical features
Idiopathic Polymorphic light eruption (PLE) Itchy, papulovesicular rash on photo-exposed sites; face and back of hands often spared. Often hours of UVR exposure needed to provoke; lasts a few days; affects 20% in Northern Europe, more common in young women
Chronic actinic dermatitis (CAD) Chronic dermatitis on sun-exposed sites. Most common in elderly males. UVB, UVA and often visible light photosensitivity. Most also have contact allergies
Solar urticaria Immediate-onset urticaria on photo-exposed sites, usually UVA and visible light photosensitivity. Can occur at any age
Actinic prurigo Uncommon, presents in childhood. Often familial. Some similarities to PLE, although scarring occurs
Hydroa vacciniforme Rare childhood photodermatosis. Varioliform scarring
Drugs Variety of mechanisms Usually UVA (and visible) light photosensitivity
Phototoxicity Most common. Exaggerated sunburn and exfoliation. Many drugs such as thiazides, tetracyclines, fluoroquinolones, quinine, NSAIDs
Pseudoporphyria e.g. NSAIDs, retinoids, tetracyclines, furosemide
Photoallergy Usually to topical agents, such as sunscreens and NSAIDs
Metabolic Porphyrias
Pellagra
Mainly porphyria cutanea tarda and erythropoietic protoporphyria (p. 458). Photoexposed site dermatitis due to tryptophan deficiency (see Fig. 16.17, p. 459)
Photogenodermatoses Xeroderma pigmentosum Rare. Defect in DNA excision repair, abnormal photosensitivity, photoageing and skin cancer. May be neurological features
Photo-aggravation of pre-existing conditions e.g. Lupus erythematosus Can also be drug-induced, e.g. by thiazides (see Box 28.44, p. 1304)
Erythema multiforme p. 1302
Rosacea p. 1283

Apr 9, 2017 | Posted by in GENERAL SURGERY | Comments Off on Skin disease
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