By Dr. Marcus Judge

OSCE

During any examination in an OSCE it is important to understand the pathology and reasoning behind each of the signs and symptoms elicited. This applies even if the patient being examined is ‘normal’. This article explains how to perform a rash and non-pigmented skin lesion examination. A non-pigmented skin lesion is an area of abnormal skin that is not brown or black. The article also covers the key findings to look for, what each sign means and which conditions it may indicate.

Unlike the examination of a pigmented lesion (where the priority is to exclude melanoma), this examination is mainly about describing an inflammatory rash or a non-pigmented lesion accurately and methodically. Keep skin cancer in mind too: a non-pigmented lesion can still be a squamous cell carcinoma or a basal cell carcinoma (both types of skin cancer), or a melanoma that has little or no pigment. A clear, systematic description of site, distribution, morphology (the form and structure of the lesion) and palpation findings (what you feel when you touch the lesion) is often enough to reach a working diagnosis. The discipline of describing what you see is therefore just as important as the diagnosis itself.

Contents

  1. Introduction
  2. General Inspection
  3. Close Inspection – Site, Number and Distribution
  4. Close Inspection – Size, Shape, Colour and Margin
  5. Morphology of the Lesion
  6. Configuration and Arrangement
  7. Palpation
  8. Examination of Associated Areas
  9. Regional Lymph Nodes
  10. Completing the Examination
  11. Quiz

Introduction

Wash your hands using alcohol gel or soap and water before approaching the patient.

Introduce yourself to the patient and ensure to mention your grade e.g. 3rd year medical student/junior doctor/consultant.

Confirm the patient’s details taking 3 points of identification usually; full name, date of birth and NHS/hospital number.

Obtain consent for the examination, ensuring to explain what the examination will entail. Explain that you would like to look at and gently feel the affected skin. Say that you may also need to examine other areas, such as the nails, scalp and skin folds. Offer a chaperone (a trained person who is present to support the patient and observe the examination), particularly if examination of intimate or sensitive areas may be required.

Ask the patient if the area is painful or itchy before you begin, so that you can be gentle and avoid causing discomfort.

Expose the affected area adequately while maintaining the patient’s dignity. Remember that a localised rash may be part of a more widespread condition, so be prepared to inspect the whole skin surface in a private, well-lit environment. Good natural lighting is essential, as artificial light can alter the apparent colour of a lesion.

General Inspection

Begin by standing back and observing the patient as a whole. A skin condition is frequently the visible part of a systemic disease (a disease affecting the whole body), so a general inspection can provide valuable diagnostic clues before you focus on a single lesion.

Assess whether the patient appears comfortable or whether they are visibly scratching or distressed, which suggests an intensely itchy (pruritic) condition such as eczema (itchy, inflamed, dry skin), scabies (infestation with the itch mite) or urticaria (hives). Look for signs of being systemically unwell. A patient who is febrile (has a fever) and unwell with a widespread rash may have a serious condition such as sepsis, a severe drug reaction, erythroderma (redness of most of the skin) or a skin infection.

Look around the bedside for clues, such as emollients (moisturisers), topical steroid tubes or bandages/dressings, which indicate an ongoing skin condition and its current treatment.

Note the patient’s overall skin colour and whether the skin looks dry or oily. Look for any obvious widespread changes such as generalised redness. Erythroderma is redness (erythema) affecting 90% or more of the body surface. It is a dermatological emergency because of the risks of fluid loss, hypothermia and infection.

Close Inspection – Site, Number and Distribution

Move in to inspect the affected skin closely. Begin by describing the site and the number of lesions: is there a solitary lesion, a few lesions, or a widespread rash made up of many lesions? Then note any surrounding skin changes such as scratch marks or scaling. Lesions that are separated from each other by normal skin are described as ‘discrete’.

The distribution of a rash is one of the most useful diagnostic clues, as many conditions have characteristic patterns:

  • Extensor surfaces (the outer sides of the elbows and knees): classically affected in psoriasis (a long-term skin condition with red, scaly areas). Psoriasis also often affects the scalp and the lower back (sacral area).
  • Flexural surfaces (the bends of the body: the antecubital fossae in front of the elbows, the popliteal fossae behind the knees, the neck and the wrists): the typical distribution of atopic eczema (eczema linked to a tendency to asthma and hay fever) in older children and adults.
  • Acral (the hands and feet, the far ends of the limbs): a distal pattern seen in hand, foot and mouth disease (which also causes mouth ulcers) and in some forms of eczema and palmoplantar pustulosis (pus-filled spots on the palms and soles).
  • Follicular: lesions centred on hair follicles in areas with many oil (sebaceous) glands (face, chest, upper back), as seen in acne and folliculitis (inflamed hair follicles).
  • Photosensitive (sun-exposed) areas (face, neck, dorsum of hands): suggests a photosensitive eruption (a rash triggered by sunlight), a drug reaction, or systemic or cutaneous (skin-only) lupus erythematosus (an autoimmune disease).
  • Dermatomal: lesions confined to a single dermatome (the area of skin supplied by one spinal nerve) that do not cross the midline are characteristic of shingles (herpes zoster), reflecting reactivation of varicella zoster virus within a single sensory ganglion.
  • Symmetrical vs asymmetrical: a symmetrical, bilateral rash points towards an endogenous cause (arising from inside the body) or a systemic cause, whereas an asymmetrical or unilateral eruption may suggest an exogenous cause (arising from outside the body) such as contact dermatitis or infection.

Note whether the lesions follow lines of trauma or scratching. The development of new lesions along a scratch or scar is called the Koebner phenomenon and is seen in psoriasis, lichen planus (an itchy rash of shiny, flat-topped, purple-red spots) and vitiligo (patches of skin that lose their pigment).

Close Inspection – Size, Shape, Colour and Margin

For an individual lesion, describe its size (measured in millimetres or centimetres rather than compared to fruit), its shape, its colour and the nature of its margin (border). A useful mnemonic for structuring your description of any lesion in the exam is SCAM: Size, Colour, Associated secondary change (such as scale, crust or excoriation, meaning scratch marks) and Morphology. Add the shape and margin as you go. This helps you cover the core descriptive features before moving on to configuration and palpation.

The colour of non-pigmented lesions carries useful information. Colour also depends on skin tone: on brown or black skin, redness may be harder to see and a rash can look darker than the surrounding skin. Erythema (redness) reflects increased blood flow due to inflammation or vasodilation. A silvery-white scale overlying erythematous plaques is characteristic of psoriasis. The scale forms because keratinocytes (the main skin cells) overgrow (hyperproliferation) and keep their nuclei in the stratum corneum (the outer layer of the skin), which is called parakeratosis. A violaceous (purple) colour is suggestive of lichen planus.

The margin helps distinguish between conditions. A well-demarcated border with a clear edge between affected and normal skin is typical of psoriasis. In contrast, the ill-defined border of eczema blends gradually into surrounding skin, reflecting the diffuse nature of the inflammation.

It is important to assess whether erythema blanches on pressure. Press gently on the redness (a glass slide can be used) and observe whether it fades. Blanching erythema indicates that blood is contained within intact, dilated vessels (as in most inflammatory rashes). A non-blanching rash indicates that blood has leaked out of the vessels into the skin. A haemorrhagic, non-blanching rash with lesions larger than 2 mm is called purpura. This, or a rapidly spreading petechial or purpuric rash (petechiae are tiny red or purple spots caused by bleeding into the skin), is a red-flag sign. Strongly suspect meningococcal disease (a serious bacterial infection that can cause meningitis and sepsis) and treat it as an emergency that needs urgent transfer to hospital. Rashes can be hard to see on brown, black or tanned skin, so check all over the body and look for petechiae in the conjunctivae (the membranes lining the eyelids and covering the white of the eye).

Morphology of the Lesion

Describing the morphology – the form and structure of the lesion – using the correct terminology is a key skill in this examination. Primary lesions arise directly from the disease process, while secondary lesions result from the evolution of primary lesions or from external factors such as scratching.

Common primary lesions include:

  • Macule: a flat area of altered colour less than 1 cm in diameter (a larger flat lesion is a patch).
  • Papule: a raised lesion less than 1 cm in diameter (a larger solid lesion that lies deeper, in the dermis or the fat beneath, is a nodule; the dermis is the deeper layer of the skin).
  • Plaque: a raised, flat-topped lesion greater than 1 cm, as seen in psoriasis.
  • Vesicle: a small fluid-filled blister less than 1 cm (a larger blister is a bulla), seen in conditions such as eczema, herpes infections and bullous (blistering) disorders.
  • Pustule: a pus-filled lesion, which may be infective or sterile (as in pustular psoriasis).
  • Wheal: a transient, raised, itchy area of dermal oedema (swelling of the dermis) seen in urticaria (hives). It is caused by release of histamine (a chemical that makes small blood vessels leaky), which lets fluid leak into the dermis. Wheals classically come and go within 24 hours.

Common secondary lesions include scale (accumulated keratin), crust (dried exudate, the fluid that oozes from damaged skin), excoriation (scratch marks), lichenification (thickened skin with exaggerated markings from chronic rubbing) and fissures (linear cracks). Their presence helps gauge the chronicity of a condition (how long it has been present). Lichenification, for example, indicates long-standing scratching as in chronic eczema.

Plaque psoriasis on the back

Image - Well-demarcated, erythematous plaques with silvery scale on the back, typical of chronic plaque psoriasis

Creative commons source by Marnanel [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

Configuration and Arrangement

When multiple lesions are present, describe how they are arranged in relation to one another, as the pattern often points to a specific diagnosis:

  • Discoid (nummular): coin-shaped, round lesions, as seen in discoid eczema.
  • Annular: ring-shaped, with an active edge and central clearing. This is classically seen in fungal infections such as tinea (ringworm), where the fungus spreads outwards leaving healing skin behind.
  • Linear: arranged in a line, which may reflect the Koebner phenomenon or external contact (e.g. a plant brushing the skin in contact dermatitis).
  • Target (targetoid): concentric rings of colour, typically three zones (a dusky centre, a paler swollen ring and a red outer edge), characteristic of erythema multiforme (a skin reaction, often triggered by an infection such as herpes simplex or by a medicine).
  • Grouped (herpetiform): clustered vesicles or papules on an erythematous base, as seen in herpes simplex and dermatitis herpetiformis (an itchy, blistering rash linked to coeliac disease).
  • Serpiginous: a wavy, snake-like track, classically made by a burrowing hookworm larva in cutaneous larva migrans (a skin infection caused by hookworm larvae from animal faeces in soil or sand).
  • Reticulate: a net-like or lacy pattern.
  • Confluent: individual lesions merging together into larger areas.

Noting the configuration alongside the distribution and morphology allows you to build a precise verbal description, which is the cornerstone of dermatological diagnosis and communication.

Urticarial wheals on the skin

Image - Urticaria, showing raised wheals of dermal oedema caused by histamine release; these lesions are transient and usually very itchy

Public Domain Source George Henry Fox [Public domain]

Palpation

Before touching the skin, ask again about pain. Put on gloves if there is any risk that the lesion is infective or likely to expose you to bodily fluids such as blood or pus. Palpation provides information that cannot be obtained by inspection alone.

Assess the following:

  • Surface texture: note whether the lesion feels smooth or rough. A rough, scaly surface (e.g. a psoriatic plaque) reflects an abnormal, thickened stratum corneum.
  • Elevation: confirm by touch whether the lesion is flat, raised above the skin, or depressed below it, which can be difficult to judge by sight alone.
  • Consistency: note whether the lesion feels soft, firm or hard. A firm or indurated (abnormally hard) lesion suggests dermal involvement.
  • Fluctuance: a fluctuant (boggy, fluid-filled) swelling that transmits a wave between two fingers suggests a collection of fluid or pus, as in an abscess.
  • Temperature: use the back of your hand to compare the lesion with surrounding skin. Warmth indicates increased blood flow due to active inflammation or infection (e.g. cellulitis, a bacterial infection of the deeper skin, or an abscess).
  • Tenderness: gentle pressure helps identify a painful, inflamed or infected lesion.
  • Mobility: assess whether a lesion is freely mobile over deeper structures or tethered (fixed). A fixed lesion is attached to deeper tissue, so consider deeper or malignant (cancerous) pathology.

If a fluid-filled lesion is present, you may comment on whether it is tense (tightly filled) or flaccid (loose and easily burst), which helps differentiate between types of blistering disorder. For example, pemphigus (an autoimmune disease) causes blisters that burst easily.

Examination of Associated Areas

Many skin conditions affect more than just the skin, so a thorough examination includes inspecting the nails, scalp and hair, and mucous membranes. These sites can confirm a diagnosis suspected from the rash.

Inspect the nails for changes that accompany skin disease:

  • Pitting: small depressions in the nail plate (the hard part of the nail), seen in psoriasis and reflecting abnormal keratinisation (keratin formation) of the proximal nail matrix (the tissue at the base of the nail where the nail grows).
  • Onycholysis: separation of the nail plate from the nail bed. It is seen in psoriasis but is not specific to it: fungal infection, injury and thyroid disease can also cause it.
  • Subungual hyperkeratosis (thickened skin under the nail) and a yellow-brown ‘oil drop’ discolouration, also features of nail psoriasis.

Look at the elbows and other extensor sites, which can show diagnostic clues away from the main rash. Well-demarcated scaly plaques here support a diagnosis of psoriasis. Firm yellowish deposits over the tendons are xanthomas (fatty deposits), which can point to a lipid disorder such as familial hypercholesterolaemia (an inherited cause of high cholesterol). Firm lumps under the skin over the olecranon (the bony point of the elbow) suggest rheumatoid nodules in a patient with rheumatoid arthritis.

Examine the scalp and hair, as psoriasis and seborrhoeic dermatitis (greasy, flaky red skin) commonly affect the scalp, and some conditions (such as discoid lupus, a form of lupus that affects the skin, and lichen planus) can cause scarring hair loss (alopecia).

Inspect the mucous membranes of the mouth (and, where relevant and with appropriate chaperoning, the genital mucosa). Oral involvement is seen in lichen planus (a lacy white network known as Wickham’s striae) and in conditions such as erythema multiforme and pemphigus.

Regional Lymph Nodes

Palpate the regional lymph nodes that drain the affected area of skin. Skin infections, inflammatory conditions and malignancies can all cause the draining nodes to become enlarged.

Lymphadenopathy (enlarged lymph nodes) accompanying a skin lesion may indicate a local infection (such as cellulitis or an infected lesion), an inflammatory skin disease or, importantly, spread from a skin malignancy (skin cancer). Note the size, consistency, tenderness and mobility of any palpable nodes. Tender, mobile nodes suggest a reactive (infective or inflammatory) cause, whereas hard, fixed, non-tender nodes are more concerning for malignancy.

Atopic dermatitis in the flexure of a child's arm

Image - Atopic eczema affecting the flexor surface of the arm, showing erythema with an ill-defined border; contrast this with the sharply demarcated plaques of psoriasis

Creative commons source by Eisfelder [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

Completing the Examination

Thank the patient, ensure they are covered and comfortable, and wash your hands.

Summarise your findings in a structured way. Describe the site and distribution, the morphology and configuration of the lesions, their size, colour and margin, and the relevant palpation findings. Then add any associated nail, scalp, mucosal or lymph node changes.

To complete the examination, state that you would like to:

  • Take a full dermatological history, including the onset and evolution of the rash, associated symptoms (itch, pain) and triggers. Also ask about personal and family history of atopy (a tendency to asthma, hay fever and eczema) or skin disease, drug history (for possible drug reactions) and the impact on the patient’s quality of life.
  • Perform a full skin examination of the entire skin surface if not already done.
  • Consider bedside tests such as dermoscopy (examining the skin with a lit, magnifying dermatoscope), skin swabs for microscopy and culture if infection is suspected, and skin scrapings for fungal microscopy in suspected tinea.
  • Arrange relevant investigations, such as a skin biopsy for histological diagnosis (diagnosis from examining the tissue under a microscope). Other examples are patch testing for suspected allergic contact dermatitis, and blood tests if a systemic or autoimmune cause is suspected.

A dermatoscope being used to examine a skin lesion

Image - A dermatoscope (dermoscopy) gives a magnified, illuminated view of a lesion's surface, supporting diagnosis at the bedside

SimpleMed original

Quiz

Preview the Rash and Non-Pigmented Skin Lesion OSCE Examination quiz

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