Chapter 119: A diagnostic and management approach to skin problems

The diagnosis of skin problems depends on astute clinical skills based on a systematic history and examination and, of course, experience. If the diagnosis is in doubt, it is appropriate to refer the patient to a skilled cooperative consultant, as the referral process is an excellent educational opportunity for the GP. Another opinion from a colleague/s in a group practice is also very educative. At least, cross-referencing the skin lesion with a colour atlas facilitates the learning process.

Primary lesions

• Macule. Circumscribed area of altered skin colour (Latin for stain) without elevation <1 cm diameter (see FIG. 119.1).

• Patch. Macule of >1 cm diameter (see FIG. 119.1).

• Papule. Palpable mass on skin surface <0.5 cm diameter (see FIG. 119.2).

• Maculopapule. A raised and discoloured circumscribed lesion.

• Nodule. Circumscribed palpable mass >0.5 cm diameter (see FIG. 119.2).

• Plaque. A flat-topped palpable mass >1 cm diameter.

• Wheal. An area of dermal oedema (can be any size), which is pale and compressible.

• Angio-oedema. A diffuse area of oedema extending into subcutaneous tissue.

• Vesicle. A fluid-filled blister <0.5 cm in diameter (see FIG. 119.3).

• Bulla. A vesicle >0.5 cm diameter (see FIG. 119.3).

• Pustule. A visible collection of pus in the skin <1 cm diameter.

• Abscess. A localised collection of pus in a cavity >1 cm diameter.

• Furuncle. A purulent infected hair follicle; includes:

  • – folliculitis (small furuncles)

  • – boils (larger furuncles)

• Carbuncle. A cluster of boils discharging through several openings.

• Purpura. A circumscribed deposit of blood >0.5 cm in diameter. May be macular or papular.

• Petechiae. Purpuric lesions <0.5 cm in diameter.

• Ecchymosis. Larger purpuric lesion.

• Haematoma. A swelling from gross bleeding.

• Telangiectasia. Visible dilatation of small cutaneous blood vessels.

• Comedo. A plug of keratin and sebum in a dilated pilosebaceous gland.

• ‘Blackhead’. An open comedo.

• ‘Whitehead’. A closed comedo.

• Erythema. Redness of the skin due to increased vascularity.

• Milium. Tiny white cyst containing keratin, from occlusion of pilosebaceous gland.

• Papilloma. Warty projection above the skin surface.

Secondary lesions

• Scales. An accumulation of excess keratin that presents as flaking.

• Crusts (scabs). Superficial dried secretions (serum and exudate).

• Ulcer. A circumscribed deep defect with loss of all the epidermis and part or all of the dermis (see FIG. 119.4); they usually heal with scarring.

• Erosion. A skin defect with complete or partial loss of the epidermis; they heal without scarring (see FIG. 119.4).

• Fissure. A linear split in the epidermis and dermis (see FIG. 119.4).

• Atrophy. Thinning or loss of epidermis and/or dermis with loss of normal skin markings.

• Sclerosis. Thickening of the dermis with induration of subcutaneous tissue; resembles a scar but may arise spontaneously (e.g. scleroderma).

• Scar. A healed dermal lesion where normal structures are replaced by fibrous tissue.

• Hypertrophic scar. Rises above the skin surface.

• Atrophic scar. Settles below the skin surface.

• Keloid. Overgrowth of dense fibrous tissue extending beyond the original wound.

• Excoriation. Scratch marks causing an erosion or an ulcer (loss of epidermis).

• Acanthosis. Thickening of skin without accentuation of skin markings.

• Lichenification. Thickening secondary to chronic scratching or rubbing (in dermatitis).

• Callus. Localised hypertrophy of the stratum corneum.

• Exfoliation. Loss of epidermal keratin as large scales or sheets.

• Keratoderma. Thickening of skin especially stratum corneum.

The diagnostic approach of Robin Marks¹ presented here helps to achieve order in the midst of confusion. He describes the importance of simplifying the diagnostic process by being a ‘lumper’ rather than a ‘splitter’. Most common dermatological problems fall into one of seven categories (see TABLE 119.1). A problem that does not fit into one of these seven groups is either an unusual condition or an unusual presentation of a common condition and probably merits a consultant’s opinion.

Note: TABLES 119.1 to 119.6 were prepared by Professor Robin Marks¹ and are reproduced with his permission.

History

The three basic questions are:¹

1. Where is the rash and where did it start?

2. How long have you had the rash?

   Note: The split into three time zone groups (see TABLE 119.2) is very useful. This question leads on to the next question regarding itch, as the patient is unlikely to tolerate an itchy eruption.

3. Is the rash itchy?

   If so, is it mild, moderate or severe? The nature of the itch is very helpful diagnostically. A severe itch is one that wakes the patient at night and leads to marked excoriation of the skin, while a mild itch is one that is only slightly upsetting for the patient and may not be noticeable for significant periods during the day.

Three questions the doctor must consider

1. Could this be a drug rash?

2. Has this rash been modified by treatment?

3. Do any contacts have a similar rash?

• Do you have contact with a person with a similar eruption?

• What medicines are you taking or have you taken recently?

• Have you been exposed to anything different recently?

• Do you have a past history of a similar rash or eczema or an allergic tendency (e.g. asthma)?

• Is there a family history of skin problems?

The characteristics of the itch are very useful in dividing up the diagnoses: an eruption that is not itchy is unlikely to be scabies and one that is very itchy is unlikely to be a skin tumour (see TABLE 119.3).

However, nothing is absolute and variations to the rule will occur—tinea, psoriasis and pityriasis versicolor are sometimes itchy and sometimes not. Chickenpox can vary from being intensely itchy, especially in adults, to virtually no itching.

Relieving or aggravating factors of the itch provide useful diagnostic guidelines; for example, Whitfield’s ointment applied to an itchy eruption for a provisional diagnosis of ringworm would make the itch worse if it were due to eczema.

Examination¹

Examine the skin in good light, preferably natural light, and ensure that any make-up is removed.

There are two basic stages in the physical examination of a rash. The first is an assessment of the characteristics of the individual lesion and the second is the distribution or pattern of the lesions.

Characteristics of the individual lesion

The single most important discriminating feature is whether it involves the dermis alone or the epidermis as well (see TABLE 119.4). If the lesion involves the epidermis there will be scaling, crusting, weeping, vesiculation or a combination of these (see FIG. 119.5). If the dermis alone is involved, the lesion is by definition a lump, a papule or a nodule (see FIG. 119.6). No lesion ever involves the epidermis without involving the dermis as well.

Other characteristics of individual lesions that must be sought are the colour, the shape and the size. It is important to feel the skin during the physical examination and to note the consistency of the lesion. Is it firm or soft? The activity of the lesion may also be useful: does it have a clearing centre and an active edge?

Distribution of the lesions

The clinician must decide whether the lesions are localised or widespread. If they are widespread, are they distributed centrally, peripherally, or both? (See TABLE 119.5.) Diagnosis is often helped when the skin lesions are in a specific area (see TABLE 119.6 and FIGS 119.7 and 119.8). Itchy papules on the penis associated with a widespread pruritus are likely to be scabies. However, care has to be taken because many misdiagnoses are made instinctively on the distribution (e.g. anything in the flexures is dermatitis or anything on the feet is tinea).

Another feature of an eruption, which should be sought on examination, is whether the lesions are all at the same stage of evolution.

It is necessary to perform a complete physical examination as well. There is, after all, no such thing as a skin disease but rather disease affecting the skin. The clinician must always bear this in mind when managing patients complaining of a skin eruption. Disease does not affect the skin in isolation and it is unforgivable to look only at the skin and ignore the patient as a whole.

Note: In every case examine the mouth, scalp, nails, hands and feet.

Appropriate diagnostic tools include:

• a magnifying lens

• a diascope, which is a glass slide or clear plastic spoon that is used to blanch vascular lesions in order to determine their true colour

• a ‘Maggylamp’, which is a hand-held fluorescent light with an incorporated magnifier; the device allows shadow-free lighting and magnification

• a dermatoscope, which is very valuable in the diagnosis of pigmented tumours but it does require skill and familiarity to achieve effective use

• Wood’s light

• swabs for culture and NAAT test (PCR)

• skin scrapings or nail clippings for dermatophyte culture

• skin biopsy (even with psoriasis, etc.)

Wood’s light

Wood’s light examination is an important diagnostic aid for skin problems in general practice. It has other uses, such as examination of the eye after fluorescein staining. (A low-cost, small ultraviolet light unit called ‘the black light’ is also available.)

Method

Simply hold the ultraviolet light unit above the area for investigation in a dark room.

Not all cases of tinea capitis fluoresce because some species that cause the condition do not produce porphyrins as a by-product. See TABLE 119.7 for a list of the skin conditions that do fluoresce. Wood’s light is really only useful for hair-bearing areas.

Porphyrins wash off with soap and water, and a negative result may occur in a patient who has shampooed the hair within 20 hours of presentation. Consequently, a negative Wood’s light reading may be misleading. The appropriate way of confirming the clinical diagnosis is to send specimens of hair and skin for microscopy and culture.

Skin scrapings for dermatophyte diagnosis

Skin scrapings are an excellent adjunct to diagnosis of fungal infections. Requirements are a scalpel blade, glass slide and cover slip, 20% potassium hydroxide (preferably in dimethyl sulphoxide) and a microscope. Skin scrapings can also be sent for microscopy and culture.

Clinical indications:

1. tinea (superficial dermatophyte infection)

2. pityriasis versicolor

3. Candida

Method

• Scrape skin from the active edge.

• Scoop the scrapings onto the glass microscope slide.

• Cover the sample with a drop of potassium hydroxide.

• Cover this with a cover slip and press down gently.

• Warm the slide and wait at least 5 minutes for ‘clearing’.

• Examine at first under low power with reduced light.

• When fungal hyphae are located, change to high power.

• Use the fine focus to highlight the hyphae (see FIG. 119.9).

Note: Some practice is necessary to recognise hyphae.

Detection of the scabies mite: the burrow of the scabies mite is found (can be difficult!) and the epidermis is decisively scraped with a no. 15 scalpel blade, and transferred to a slide after adding a drop of liquid paraffin. The mite is very distinctive.

Patch testing

Patch testing is used to determine allergens in allergic contact dermatitis. Read in 48 hours.

Biopsies

Shave or punch biopsies can be useful (see FIGS 124.26 and 124.27 in CHAPTER 124).

Hair²

Send hair samples for microscopy and root analysis. There are two main tests:

1. the hair pull test (refer CHAPTER 126)

2. the hair pluck test

In the hair pluck test (used for tinea capitis and hair shaft disorder), a tuft of about 20 hairs is drawn out, forceps applied close to the skin of the scalp and rotated slightly prior to sharp extraction. The hair should be collected on a glass slide for counting and analysis.

• Ointment formulations are generally more potent than creams. This is because the occlusive nature of an ointment enhances absorption of the corticosteroid.

• Creams contain more preservatives and excipients than ointments, and so are more likely to cause hypersensitivity or irritation.

• Ointments are generally recommended over creams.

• A cream base may be used for an acute weeping rash.

• Use a gel or lotion for hair-bearing areas.

• Stubborn dermatoses may benefit from occlusion, such as plastic wrap, occlusive dressings or gloves, applied overnight with appropriate securing in place.

• Choose a potency of corticosteroid appropriate to the site of the rash.

• The greatest absorption occurs through thin skin of eyelids, genitals and skin creases, where a mild corticosteroid should be used.

• The least absorption occurs through the thick skin of palms and soles, where a potent corticosteroid should be used.

• Use a moderately potent corticosteroid on the rest of the limbs and trunk.

• For Candida infection (e.g. secondary infection of irritant napkin dermatitis), mix 1% hydrocortisone in equal quantities with an antifungal preparation such as nystatin.

Topical corticosteroids for chronic dermatoses

• Assure patients and parents that the benefits of topical corticosteroids outweigh the harms, and that they should not be afraid to use them.

• Once daily use is usually sufficient and encourages concordance with therapy.

• Apply liberally, not sparingly.

• Use on all areas of inflammation until the skin is perfectly clear.

• Maintain remission by using an emollient often.

• Resume topical corticosteroids promptly to control periodic flares.

• Avoid high-potency preparations on the face, in flexures and on infants.

• Corticosteroids can mask or prolong an infection.

• Adverse effects of long-term use are rare and include skin atrophy, striae, peri-oral dermatitis and steroid rosacea.

The relative clinical potency of topical corticosteroids is given in TABLE 119.8.

• Do no harm. Introduce the mildest possible preparation to alleviate the problem.

• Creams tend to be drying, lotions even more so.

• Ointments tend to reduce dryness and have greater skin penetration. If wet—use a wet dressing (wet soaks and a lotion). If dry—use an ointment (salve).

• Occlusive dressings with plastic wraps permit more rapid resolution of stubborn dermatoses.

• Most toilet soaps are alkaline and are very drying; they should not be used on dry skin or dermatitis with dry skin. Soap substitutes include neutral soaps (Dove, Neutrogena), superfatted soaps (Oilatum) and non-soap cleanser (Cetaphil).

• Bath additives can be useful for dermatoses such as psoriasis, atopic dermatitis and for pruritus. For some people it may be better not to add it to the bath (diluting effect; accident from slipping) but to massage the oil into the dry itchy skin after the bath.

• Always give careful instructions to the patient regarding application of preparations: use a prepared handout if available.

• Alter the treatment according to the response.

• Explain the costs involved, especially where a preparation is expensive.

How much?⁴

On average, 30 g of cream will cover the body surface area of an adult. The ‘rule of nines’, used routinely to determine the percentage of body surface area affected by burns (see FIG. 119.10), may also be used to calculate the amount of a topical preparation that needs to be prescribed.

For example:

• if 9% of the body surface area is affected by eczema, approximately 3 g of cream is required to cover it

• 9 g of cream is used per day if prescribed three times daily

• a 50 g tube will last 5–6 days

One gram of cream will cover an area approximately 10 cm × 10 cm (4 square inches), and this formula may be used for smaller lesions.

TABLE 119.9 provides guidelines for approximate weekly quantities of skin preparations required to cover specific areas of the body.

Some general rules

Remember:

• that 30 g

  • – will cover the adult body once

  • – will cover hands twice daily for 2 weeks

  • – will cover a patchy rash twice daily for 1 week

• that 200 g will cover a quite severe rash twice daily for 2 weeks