The commonest cause of a slightly itchy eruption of acute onset in a young person which lasts over a week is pityriasis rosea. In many cases the history alone suggests the diagnosis as the condition starts with a solitary lesion commonly found in the scapular area or lower abdomen, oval in shape, slightly scaly and red. Three or four days later an eruption appears which, within a few days, involves most of the trunk. This should be viewed from a distance, preferably by daylight and it will be seen to form a pattern on the trunk in that the macules, which are one of its components, are arranged with their long axis in the lines of cleavage of the skin which correspond roughly to the lines of the ribs in the thorax and transverse lines in the abdominal and lumbar areas. Involving the trunk mainly, it usually ceases on the upper thighs and upper arms and is thus described as confined to the vest and pants area.
Closer inspection reveals that there are two components, pink papules and oval macules, the proportion of which varies; when papules predominate the diagnosis may be more difficult. The configuration of the macules is often best preserved on the flanks where rubbing and scratching is less. Usually 2 to 3 cm in their long axis they have a pink areola and a fawn coloured centre. At the margin of the fawn area there is scaling which is characteristically centripetal. There is no systemic disturbance apart from itching which varies from slight to severe in different patients and there are no other physical signs.
This is the classical picture of pityriasis rosea which is easy to diagnose, but there, are variations on this theme. In the first place the herald patch may remain the only sign for anything up to four weeks before the generalised rash appears. Usually the face and neck are spared but when the neck is involved the macules coalesce to form a reticular scaly eruption which, if it extends to the face, becomes a confluent scaly erythema. In the later stages of the eruption it commonly extends down the arms and legs as it fades on the trunk but, occasionally, the arms and legs are predominantly involved from the onset and sometimes macules may also appear on the palms. Rarely the macules are so large that they are mistaken for ringworm.
The differential diagnosis is important as it is such a common problem. Tinea pedis may produce a sensitisation eruption consisting of macules very like pityriasis rosea but usually more pronounced on the limbs.
Seborrhoeic dermatitis may give rise to a macular eruption on the trunk but this is usually scattered at random, without the patterning of pityriasis rosea; other stigmata of seborrhoeic dermatitis accompany it, such as scurfy scalp, otitis externa, blepharitis and flexural intertrigo. In the end persistence for longer than is usual with pityriasis rosea may be the main clue.
Guttate psoriasis often starts after a sore throat and the lesions are dotted at random over limbs and trunk. They are uniformly scaly and round rather than oval; the scalp is frequently involved and here palpable scaly discs are produced.
Secondary syphilis should always be in one’s mind in such a differential diagnosis, even though it is now rare. Concomitant signs are usually present and the Wassermann and Kahn reactions should be performed in any case where this diagnosis is even faintly possible.
The cause of pityriasis rosea is unknown; the herald patch followed by a generalised rash which attacks the young and does not usually recur suggests an infection such as a virus, but so far there is no confirmation.
The eruption lasts about 6 weeks from the time of generalisation; in some it may disappear more quickly, in others it may spread down the arms and legs as it clears on the trunk and take anything up to 12 weeks before it has completely resolved.
Treatment. Many patients suffer so little discomfort that no treatment need be given other than advice to avoid too hot baths, which cause itching. Others itch violently and can be relieved by application of a dilute corticosteroid cream and an antipruritic drug such as promethazine (Phenergan) mgms 50 at night. If there is any special urgency for the eruption to be cleared, ultra-violet light therapy in suberythema doses three times weekly is worth trying though not always effective.
The sufferer from lichen planus usually complains of an itching eruption of sudden onset, starting on the wrists and spreading to trunk and legs. Once established its course is prolonged and by the time advice is sought the rash may have been present for weeks or months.
The skin should be examined by daylight if possible and it will be found that the papular eruption tends to involve the flexural aspect of the wrists and forearms, the trunk and the shins. In a severe attack it may spread beyond these areas or in a mild attack may only present a few lesions on wrists or shins.
The individual lesions are highly characteristic, consisting of purplish, flat topped, shiny papules, polygonal in outline and often umbilicated. Papules frequently occur in scratch marks (Koebner’s phenomenon). A magnified lesion can be seen to have the purplish colour broken by a network of Wickham’s striae which are delicate white lines. The histological changes of lichen planus are hyperkeratosis and a patchy increase in thickness of the stratum granulosum, a band like infiltrate of mainly lymphocytes hugging the epidermis and irregular acanthosis giving rise to a saw-tooth appearance of the papillae. On the shins the lesions become warty, larger and form plaques which still retain the characteristic colour.
In very severe cases the papules are so numerous that they coalesce, giving the affected areas a solidly purplish colour and, very rarely, small tense vesicles may appear. On palms and soles the colour change is less evident and the papules appear as rather translucent lesions resembling vesicles but hard and hyperkeratotic. In more chronic cases the lesions on the trunk assume an annular pattern.
Mouth lesions are an important aid to diagnosis and may occur in the absence of any skin lesions. They can be present at the onset of the eruption, arise during its course or never appear at all. Delicate white striae on the buccal mucosa opposite the premolar teeth are commonest, but they can be annular lesions or profuse white dots, resembling moniliasis but immovable. Similar lesions may appear on the tongue and white striae appear on the red margin of the lip. Indolent ulcers occur in a few cases, which tend to protrude a plateau of granulation tissue flecked with yellow exudate; the edges of the ulcer, still showing white striae, may also be scarred. Such ulceration occurs at the sides of the tongue and on the buccal mucosa, it is uncomfortable and tender but not acutely painful like aphthous ulcers. Like all chronic inflammatory lesions of mucocutaneous junctions these ulcers are potentially malignant. In such a site epitheliomata grow rapidly and mouth ulceration should be reviewed at frequent intervals. Similar striae and white patches may appear on the vulva and have even been described on the rectal mucosa. Lesions on the glans penis may be papular or annular and if they occur in the absence of lesions elsewhere the patient may develop fear of venereal infection.
A rare variant known as lichen planopilaris may produce irregular scarred patches of permanent alopecia in the scalp and follicular hyperkeratosis over the upper back which gives it the feel of a nutmeg grater.
Children are rarely affected and when they are the lesions are atypical, sometimes giving rise to widespread small verrucose lesions which may be mistaken for psoriasis. Rarely the nails may be involved, usually giving rise to longitudinal ridging and splitting of the nail plate but sometimes causing such severe atrophy of the plate that it is almost completely destroyed. Like psoriasis linear lesions may be produced on the trunk or a limb, having a distribution which falsely suggests neurogenesis. Koebner’s phenomenon may also cause lichen planus to become superimposed on the other skin lesions, so that as an eczema or exfoliative dermatitis fades and heals, lichen planus may suddenly break out on the same areas.
Aetiology. The aetiology of lichen planus is unknown. In a few cases the coincidence with shock or worry is very striking but the majority of patients can blame nothing specific. Several unrelated drugs can cause an eruption which is identical even to the presence of mouth lesions. Organic arsenicals, gold, mepacrine, chloroquine, amiphenazole (Daptazole), methyldopa and paraminosalicyclic acid (P.A.S.) characteristically cause a lichenoid eruption which in the case of slowly excreted, heavy metals and anti-malarial drugs persists for long after administration has been stopped.
The course of lichen planus is very variable and in general the acute generalised attack seems to resolve more rapidly, the lesions becoming flat, losing their bright colour and turning brown; pigment only may remain after about 3 months. The average duration of the ordinary pattern of lesions is about 6 months. One tenth of patients suffer chronic lesions which last for years, hypertrophic and annular lesions being those which persist the longest. Most patients have only one attack but some suffer at intervals over many years.
Treatment. There is no specific treatment but in most cases resolution can be speeded by the application of fluorinated steroid ointments at night under polythene occlusion. In cases with localised lesions such treatment presents no difficulty but even when lesions are widespread it is possible to treat the arms for a fortnight, then legs, then trunk and if the local application is continued without occlusion on these areas there is usually no recurrence.
Chronic hypertrophic lesions which do not respond to local steroid therapy can be treated by infiltrating the lesion with hydrocortisone or triaminolone which is injected subcutaneously fortnightly, using 1 ml per injection.
Ordinary mouth lesions are usually symptomless and require no treatment since they fade with the skin lesions. Ulcerated lesions and those occurring in the absence of skin lesions usually respond to the application of triaminolone in Orabase twice daily.
When very widespread, the itching can be most distressing and it is helpful to rest the patient in bed while treating with local corticosteroids under polythene occlusion. If there is no response and provided there is no systemic contraindication prednisolone should be given by mouth starting with a dose of 30 mg daily, maintaining this for 10 to 14 days, in which time eruption should have faded, then gradually weaning the patient off the drug.