Familiarity with the clinical features of psoriasis and eczema, which all clinicians see from time to time, provides a basis for comparison with other rather less common conditions.
The characteristics that each condition has in common with psoriasis and eczema are highlighted in the relevant tables.
Lichen planus
Like psoriasis, the lesions are well defined and raised.
They also occur in areas of trauma the Koebner’s phenomenon.
There is no constant relation to stress.
Unlike psoriasis, there is no family history.
Itching is common.
The distribution is on the flexor aspects of the limbs, particularly the ankles and wrists, rather than on the extensor surfaces, as in psoriasis.
It also occurs on the trunk.
However, localised forms of lichen planus can occur on the shin, palm, and soles or elsewhere. Nail involvement is less common than in psoriasis.
There may be thinning and atrophy of part or all of a nail and these often take the form of a longitudinal groove, sometimes with destruction of the nail plate.
The oral mucosa is commonly affected with a white, net-like appearance and sometimes ulceration.
The typical flat topped lesions have a shiny hyperkeratotic lichenified surface with a violaceous colour, interrupted by milky white streaks Wickham’s striae.
Less commonly, very thick hypertrophic lesions occur and also follicular lesions.
Lichen planus is one cause of localised alopecia on the scalp as a result of hair follicle destruction.
Lichen planus usually resolves over many months to leave residual brown or grey macules.
In the oral mucosa and areas subject to trauma ulceration can occur.
Treatment
There is usually a gradual response to topical steroids, but in very extensive and inflamed lesions systemic steroids may be needed.
Localised hypertrophic lesions can be treated with intralesional injections. Similar rashes
Lichenified eczema
This is also itchy and may occur on the ankles and wrists.
The edge of the lesion is less well defined and is irregular.
The flat topped, shiny papules are absent.
Guttate psoriasis
Guttate psoriasis is not as itchy as lichen planus.
Scaling erythematous lesions do not have the lichenified surface of lichen planus.
Pityriasis lichenoides
The lesions have a mica-like scale overlying an erythematous papule.
Drug eruptions
Rashes with many features of lichen planus can occur in patients taking:
• Chloroquine
• Chlorpropamide
• Chlorothiazide
• Anti-inflammatory drugs
• Gold preparations
It also occurs in those handling colour developers.
Treatment
The main symptom of itching is relieved to some extent by moderately potent steroid ointments.
Very hypertrophic lesions may respond to strong steroid preparations under polythene occlusion.
Careful intralesional injections may be effective in persistent lesions.
In very extensive, severe lichen planus systemic steroids may be indicated.
Pathology of lichen planus
As expected from the clinical appearance, there is hypertrophy and thickening of the epidermis with increased keratin.
The white streaks seen clinically occur where there is pronounced thickness of the granular layer and underlying infiltrate.
Degenerating basal cells may form “colloid bodies”.
The basal layer is being eaten away by an aggressive band of lymphocytes, the remaining papillae having a “saw toothed” appearance.
Seborrhoeic dermatitis
Seborrhoeic dermatitis has nothing to do with sebum or any other kind of greasiness.
There are two distinct types, adult and infantile.
Adult seborrhoeic dermatitis
The adult type is more common in men and in those with a tendency to scaling and dandruff in the scalp.
There are several commonly affected areas:
• Seborrhoeic dermatitis affects the central part of the face, scalp, ears, and eyebrows.
There may be an associated blepharitis, giving some red eyes and also otitis externa.
• The lesions over the sternum sometimes start as a single “medallion” lesion.
A flower-like “petaloid” pattern can occur. The back may be affected as well.
• Lesions also occur in well defined areas in the axillae and groin and beneath the breasts.
Typically the lesions are discrete and erythematous and they may develop a yellow crust.
The lesions tend to develop from the hair follicles.
It is a persistent condition that varies in severity. Clinically and pathologically the condition has features of both psoriasis and eczema.
There is thickening of the epidermis with some of the inflammatory changes of psoriasis and the intercellular oedema of eczema.
Parakeratosis the presence of nuclei above the basement layer may be noticeable. Recently, increased numbers of Pityrosporum ovale organisms have been reported.
Treatment
Topical steroids produce a rapid improvement, but not permanent clearing.
Topical preparations containing salicylic acid, sulphur, or ichthammol may help in long term control.
Triazole antifungal drugs by mouth have been reported to produce clearing and can be used topically.
These drugs clear yeasts and fungi from the skin, including P. ovale, which is further evidence for the role of this organism.
Infantile seborrhoeic dermatitis
In infants less than six months old a florid red eruption occurs with well defined lesions on the trunk and confluent areas in the flexures associated with scaling of the scalp.
There is no consistent association with the adult type of seborrhoeic dermatitis.
It has been suggested that infantile seborrhoeic dermatitis is a variant of atopic eczema.
It is said to be more common in bottle fed infants.
A high proportion of affected infants develop atopic eczema later but there are distinct differences. Itching is present in atopic eczema but not in seborrhoeic dermatitis.
The clinical course of atopic eczema is prolonged with frequent exacerbation, whereas seborrhoeic dermatitis clears in a few weeks and seldom recurs.
Treatment comprises emollients, avoiding soap, and applying hydrocortisone combined with an antibiotic plus nystatin (for example, Terra-Cortril plus nystatin cream).
Hydrocortisone can be used on the scalp. Allergy IgE concentrations are often raised in atopic eczema and food allergy is common, but not in seborrhoeic dermatitis.
Perioral dermatitis
Perioral dermatitis is possibly a variant of seborrhoeic dermatitis, with some features of acne.
Papules and pustules develop around the mouth and chin.
It occurs mainly in women.
Pityriasis rosea
The word “pityriasis” is from the Greek for bran, and the fine bran-like scales on the surface are a characteristic feature.
The numerous pale pink oval or round patches can be confused with psoriasis or discoid eczema.
The history helps because this condition develops as an acute eruption and the patient can often point to a simple initial lesion the herald patch.
There is commonly slight itching.
Pityriasis rosea occurs mainly in the second and third decade, often during the winter months. “Clusters” of cases occur but not true epidemics.
This suggests an infective basis.
There may be prodromal symptoms with malaise, fever, or lymphadenopathy. Numerous causes have been suggested, from allergy to fungi; the current favourite is a virus infection.
The typical patient is an adolescent or young adult, who is often more than a little concerned about the sudden appearance of a widespread rash.
The lesions are widely distributed, often following skin creases, and concentrated on the trunk with scattered lesions on the limbs.
The face and scalp may be affected. Early lesions are red with fine scales usually 1–4 cm in diameter.
The initial herald patch is larger and may be confused with a fungal infection.
Subsequently the widespread eruption develops in a matter of days or, rarely, weeks.
As time goes by the lesions clear to give a slight pigmentation with a collarette of scales facing towards the centre.
Similar rashes
Discoid eczema presents with itching and lesions with erythema, oedema, and crusting rather than scaling. Vesicles may be present.
The rash persists unchanged.
A drug eruption can sometimes produce similar lesions.
In guttate psoriasis the lesions are more sharply defined and smaller (0·5–1·0 cm) and have waxy scales.
Pathology
Histological changes are non-specific, showing slight inflammatory changes in the dermis, oedema, and slight hyperkeratosis.
Pityriasis lichenoides
Pityriasis lichenoides is a less common condition occurring in acute and chronic forms.
The acute form presents with widespread pink papules which itch and form crusts, sometimes with vesicle formation suggestive of chickenpox.
There may be ulceration. The lesions may develop in crops and resolve over a matter of weeks.
The chronic form presents as reddish brown papules—often with a “mica”-like scale that reveals a smooth, red surface underneath, unlike the bleeding points of psoriasis.
In lichen planus there is no superficial scale and blistering is unusual.
The distribution is over the trunk, thighs, and arms, usually sparing the face and scalp.
The underlying pathology vascular dilatation and a lymphocytic infiltrate with a keratotic scale is in keeping with the clinical appearance.
The cause is unknown. Treatment is with topical steroids.
Ultraviolet light treatment is also helpful.
Pityriasis versicolor
Pityriasis versicolor is a skin eruption that usually develops after sun exposure with white macules on the tanned skin but pale brown patches on the covered areas, hence the name versicolor, or variable colour.
The lesions are:
(a) flat;
(b) only partially depigmented areas of vitiligo are totally white; and
(c) do not show inflammation or vesicles.
The causative organism is a yeast, Pityrosporum orbiculare, that takes advantage of some unknown change in the epidermis and develops a proliferative, stubby, mycelial form,
Malassezia furfur.
This otherwise incidental information can be simply put to practical use by taking a superficial scraping from a lesion on to a microscope slide add a drop of potassium hydroxide or water with a coverslip.
The organisms are readily seen under the microscope as spherical yeast forms and mycelial rods, resembling “grapes and bananas” (“spaghetti and meatballs” in the United States).
Treatment is simple: selenium sulphide shampoo applied regularly with ample water while showering or bathing will clear the infection.
The colour change may take some time to clear. Ketoconazole shampoo is an effective alternative.
Oral terbinafine, which is very effective in other fungal infections, has no effect.
Desquamating stage of generalised erythema
Any extensive acute erythema, from the erythroderma of psoriasis to a penicillin rash, commonly shows a stage of shedding large flakes of skin desquamation as it resolves.
If only this stage is seen it can be confused with psoriasis.
Localised lesions with epidermal changes
Psoriasis, seborrhoeic dermatitis, atopic eczema, and contact dermatitis can all present with localised lesions. Psoriasis may affect only the flexures, occur as a genital lesion, or affect only the palms.
The lack of itching and epidermal changes with a sharp edge help in differentiation from infective or infiltrative lesions.
Seborrhoeic dermatitis can occur in the axillae or scalp with no lesions of other areas.
In atopic eczema the “classical” sites in children flexures of the elbows and knees and the face may be modified in adults to localised vesicular lesions on the hands and feet in older patients.
Some atopic adults develop severe, persistent generalised eczematous changes.
Contact dermatitis is usually localised, by definition, to the areas in contact with irritant or allergen.
Wide areas can be affected in reactions to clothing or washing powder, and sometimes the reaction extends beyond the site of contact.
Fungal infections
Apart from athlete’s foot, toenail infections, and tinea cruris (most commonly in men), “ringworm” is in fact not as common as is supposed.
The damp, soggy, itching skin of athlete’s foot is well known.
An itching, red diffuse rash in the groin differentiates tinea cruris from psoriasis. However, erythrasma, a bacterial infection, may be confused with seborrhoeic dermatitis and psoriasis skin scrapings can be taken for culture of Corynebacterium minutissimum or, more simply, coral pink fluorescence shown with Wood’s light.
The scaling macules from dog and cat ringworm (Microsporum canis) itch greatly, whereas the indurated pustular, boggy lesion (kerion) of cattle ringworm is quite distinctive.
Fungal infection of the axillae is rare; a red rash here is more likely to be due to erythrasma or seborrhoeic dermatitis.
Tinea cruris is very unusual before puberty and is uncommon in women.
In all cases of suspected fungal infection skin scrapings should be taken on to black paper, in which they can be folded and sent to the laboratory.
Special “kits” are available, which contain folded black paper and Sellotape strips on slides for taking a superficial layer of epidermis.
Lupus erythematosus
There are two forms of this condition: discoid, which is usually limited to the skin, and systemic, in which the skin lesions are associated with renal disease, arthritis, and other disorders.
There is also a subacute type with limited systemic involvement.
Systemic lupus erythematosus, which is much more common in women than men, can be an acute, fulminating, multisystem disease that requires intensive treatment, or a more chronic progressive illness.
Characteristically there is malar erythema with marked photosensitivity and a butterfly pattern.
It may be transient.
There may be scalp involvement as well with alopecia and also telangiectasia of the perifungal blood vessels.
Mouth ulcers may also be present.
Systemic involvement may cause nephritis, polyarteritis, leukopenia, pleurisy, myocarditis, and central nervous system involvement.
Systemic lupus erythematosus can present in many forms and imitate other diseases.
The facial rash can resemble rosacea, cosmetic allergy, or sun sensitivity. Systemic involvement may present with lassitude, weight loss, anaemia, arthritis, renal failure, dyspnoea, or cardiac signs among others.
Criteria for making a diagnosis of systemic lupus erythematosus have been established, of which at least four must be present.
In the subacute variety there is less severe systemic involvement, with scattered lesions occurring on the face, scalp, chest, and arms.
Treatment is with systemic steroids, with immunosuppressive agents if necessary.
Antimalarial drugs, such as hydroxychloroquine, are more effective in the subacute type.
In discoid lupus erythematosus there are well defined lesions with a combination of atrophy and hyperkeratosis of the hair follicles giving a “nutmeg grater” appearance.
They occur predominantly on the cheeks, nose, and forehead.
It is about three times as common in women as men, which is a lower ratio than in the systemic variety.
There is a tendency for the skin lesions to gradually progress and to flare up on sun exposure. It is rare for progression to the systemic type to occur.
Treatment is with moderate to very potent topical steroids and hydroxychloroquine by mouth, together with suitable sun screens.
Fixed drug eruptions
Generalised drug eruptions are considered under erythema, but there is a localised form recurring every time the drug is used.
There is usually a well defined, erythematous plaque, sometimes with vesicles.
Crusting, scaling, and pigmentation occur as the lesion heals. It is usually found on the limbs, and more than one lesion can occur.
