What Is Pruritus

Pruritus

THE sensation of itching is conveyed from the sub-epidermal plexus of nerves via the pain paths in the antero-lateral tracts of the cord. The manner in which the nervous system distinguishes between pain or itching travelling in the same pathway is not fully understood, but is probably dependent on the periodicity of the impulses. Recent experimental work has shown that proteolytic enzymes can initiate itching and it is probable that proteases released in small amounts by damage to epidermal cells accounts for itching in the absence of visible lesions.

Pruritus

A distinction has been made between spontaneous itching which arises when a new lesion such as an eczema vesicle is formed and the state of itchiness which is present in many areas of skin inflammation. In the latter condition, any trivial stimulus such as a light touch can initiate a paroxysm of itching.

There is great variation in individual capacity to feel itching, some patients hardly noticing an extensive dermatitis, whilst others suffer greatly from an eruption which is usually non-pruritic, and even in one patient, the threshold of itching varies with his state of concentration, tiredness or boredom. There are also differences in the methods of scratching for the relief of itching. In atopic eczema and papular urticaria, scratching with the finger nails until blood is diawn is the usual method of obtaining relief, whereas in urticaria rubbing with the finger pads relieves the itching and if excoriations are present this makes the diagnosis of urticaria less likely.

Generalised itching

Generalised itching, which is more marked in the evenings and in bed, is a common complaint. Having excluded parasitic diseases such as scabies and infestation with body lice, there remain a number of patients in whom no skin abnormality other than excoriations can be found. Though psychogenic irritation does occur, it is a dangerous diagnosis to make until the organic disorders, which present with itching, have been excluded by careful examination and, if necessary, laboratory investigations. Causes which should be sought are anaemia, uraemia, liver disease and systemic neoplasms and reticuloses. Normal urine, and blood urea will exclude uraemia. A complete blood count will be needed to eliminate leukaemia and severe anaemia. A marked eosinophilia should arouse suspicion of tropical or intestinal parasites. Serum iron estimation is of value as pruritis may occur when this is low especially when it is caused by lymphadenoma. Though diabetes is often quoted as a cause it is virtually unknown in clinical practice and other endocrine disorders such as hyper- and hypothyroidism are more probable.

More difficult to diagnose is itching due to liver disease especially biliary cirrhosis and cholestatic jaundice which may not be accompanied by visible jaundice. Liver function tests including mitochondrial antibody estimation and liver biopsy may be necessary to establish the cause.

Generalised itching may also precede overt evidence of Hodgkin’s disease by several years. This possibility must always be kept in mind in the young adult with intractable pruritis and a watch should be kept for superficial lymph gland enlargement and hilar lymph nodes. It may be possible to demonstrate abdominal glands by lymphangiography.

Senile pruritis
This is the most frequent cause of generalised itching in the elderly who often complain of intense itching, particularly on the back between the scapulae, yet on examination no abnormality, not even excoriations, can be found. It is probable that the heightened sensation of itchiness is a result of vascular changes in the cutaneous nerves as it is often associated with generalised arteriosclerosis, but the exact cause is unknown. The elderly also suffer from dryness and scaling of the skin, which can give rise to irritation. This dryness is accentuated by the degreasing effect of soap, if the habit of daily bathing is continued into old age. A similar condition occurring particularly in cold weather in younger age groups is termed winter itch. Senile pruritis may be complicated by dermatitis from self treatment and occasionally the symptoms are ascribed by the patient to parasitic infestation.

Treatment. The natural grease of the skin should be conserved by the restriction of bathing and the addition of emulsifying ointment or Oilatum Emollient to the bath water.

One per cent Phenol in emulsifying ointment or 3 per cent liquor picis carbonis in aqueous ointment or Boots E. 45 cream are clean and effective antipruritic and emollient applications. Lotions should be avoided, since they dry the skin and aggravate the symptoms. Explanations and reassurance plays a significant part in the relief of irritation, which may be helped by Tab. chlorpromazine hydrochloride, (Largactil) 25 mg 3 times a day. Androgenic hormones have been advocated but we have seen little benefit from their use.

Pruritus of pregnancy

A number of so called ‘toxic’ eruptions develop in the last three months of pregnancy. Usually itching is accompanied by an urticarial or an erythema multiforme—like rash, but both generalised and localised pruritus can occur without a visible skin change. Anxiety about the significance of the rash and loss of sleep produce considerable mental tension which increases the symptoms.

Reassurance that the eruption does not indicate any harm to the child and that the symptoms will clear after parturition, is of more benefit than local application, but application of wet dressings of calamine lotion give temporary symptomatic relief. Oral progesterone in the form of norethisterone 10 mg twice daily relieved itching and rash in 80 per cent of cases in a recent report. Once in 4,500 pregnancies, herpes gestationis, a bullous irritable eruption, occurs and this can be controlled only by corticosteroids.

Prurigo

This is a descriptive term for the changes in the skin which are a result of scratching and excoriation. Small, firm papules, crusts and pitted scars occur in papular urticaria, neurotic excoriations, atopic eczema, sunlight eruptions, pregnancy, old age and generalised pruritus of systemic origin. It is not a disease entity but may occur in association with severe emotional disturbance.

Localised pruritus

The commonest site for intractable localised itching is the anogenital region. Other sites have been mentioned under lichen simplex . To a great extent, the state of itchiness is due to a heightened awareness of sensation with the result that any slight stimulus is sufficient to initiate a paroxysm of itching and scratching. This damages the skin further and strengthens the conditioned reflex. Sufferers from localised pruritus are tense, excitable people but it should be remembered that intense and chronic itching may alter the mental state of an individual. Thus itching of organic origin may transform the placid, equable tempered into aggressive, complaining individuals in a remarkably short time.

Pruritus of the anogenital region has, in addition, a sexual connotation, some deriving pleasure from stimuli in this way and others using the disorder as an excuse for the refusal of sexual intercourse. Another factor is cancerphobia and, unless directly questioned, many patients will not voice their fears. There are therefore in every case both organic and psychogenic components which must be elicited by an adequate history and examination.

Pruritus ani

As has been mentioned previously, a heightened awareness of sensations is necessary for them to reach the conscious level and pruritus ani is often started by some organic lesion such as a tear in the mucosa, a fissure in ano or often an operation for haemorrhoids. Discharge from the rectum, either because of piles, proctitis or a leaking sphincter or diarrhoea may initiate itching by the production of maceration of the perianal skin. Contact dermatitis due to medicaments, particularly local anaesthetic ointments, is a common cause which may mask any underlying factor. Contact dermatitis due to toilet paper or clothing is a possibility but not a frequent offender. Local skin lesions of psoriasis, seborrhoeic intertrigo, lichen planus and ringworm may be found. Ringworm should be suspected if there are active lesions between the toes, which should always be examined. Another cause is the infection Erythrasma which can be demonstrated by its red fluorescence under Woods light. It also involves the toe clefts as well as the perineum. A very common story is that the itching followed a recent course of treatment with broad spectrum antibiotics perhaps given for an upper respiratory infection. The antibiotics by killing off other bacteria, allow Candida to increase in the intestine and spread to the perianal skin.

Infestation with threadworms is often responsible for pruritus ani in children but rarely in adults. The diagnosis can be confirmed by detection of the ova on the skin around the anus. When all these causes have been excluded, a considerable number of patients will remain in whom either no abnormality can be found or, at most, slight excoriations of the perianal skin. In some, the irritation may be associated with sweating, but in many no organic explanation can be found. It is this group which deserve investigation of psychogenic factors, though symptomatic relief can be obtained by local treatment.

Treatment. The patient should be exhorted to resist the temptation to scratch, and stimuli to the perianal region should be reduced as much as possible. Cotton wool or soft paper tissue must be substituted for toilet paper. Many patients are obsessional about cleanliness and over-use of soap and particularly antiseptics must- be avoided. A topical steroid ointment applied 3 times daily will produce relief in a high proportion of patients but atrophy follows prolonged use of powerful steroids and the atrophic skin can be easily injured by friction and sweating. It is rarely necessary to use a corticosteroid more powerful than hydrocortisone. If candida is suspected, an ointment which also contains an antiseptic such as iodochlorhydroxyquinoline (Vioform) or nystatin is to be preferred. Erythrasma responds to Erythromycin 250 mg t.d.s. and ringworm is rapidly controlled by griseofulvin. Once the pruritus is under control, applications of steroid ointment should be reduced slowly, but treatment may need to be prolonged for many months to prevent recurrence.

Pruritus vulvae

As with anal irritation, the itching may be caused by maceration of the skin from discharge which can be due to Candida or trichomonal infection of the vagina. Pregnancy and diabetes and the use of broad spectrum antibiotics all precipitate an acute candidiasis. The vivid red intertrigo of the vulva and groins with outlying vesico-pustules is a clinical picture which should indicate immediately a test for glycosuria. If one specimen of urine does not contain glucose and the clinical appearance suggests diabetes then a glucose tolerance curve should be done. Contact dermatitis caused by medicaments is always common and the possibility of sensitivity to rubber and chemical contraceptives should not be forgotten. As in the natal cleft, so the groins and vulva may be affected by psoriasis, seborrhoea and lichen planus, but ringworm is a rarity in women.

Pediculosis pubis should be considered and excluded. The presence of the lice and ova on the hairs can be easily overlooked unless a conscious effort to search for them is made.

White lesions of the vulva

A similar clinical picture is produced by three different conditions which has led to much confusion and dissention between dermatologists and gynaecologists:

(i) Lichen simplex of the vulva. This is a result of prolonged scratching due probably to a psychogenic cause. Lichenification usually involves the labia majora as well as the labia minora but sodden white keratinisation of the mucosa can resemble leucoplakia and may only be distinguishable by biopsy. If irritation can be controlled by topical steroid ointment, the white thickened areas of lichenification disappear, whereas leucoplakia remains unchanged.

(ii) Lichen sclerosus. This condition is a disorder of collagen allied to scleroderma and though usually it affects adults it can occur in childhood. There is a well defined, shiny, atrophic change in the skin over the clitoris and labia minora and lesions often extend backwards to the perianal region. Plaques of lichen sclerosus may also be found on the thighs and other parts of the body. The line of demarcation between diseased skin and the normal is very clear. The surface of the affected skin is rough and shows horny plugs and telangiectases. Itching commonly arises from infection and fissuring of the inelastic surface. Lichen sclerosus may be complicated by leucoplakia.

(iii) Leucoplakia. There is a premalignant change which may arise on the vulval mucosa which otherwise shows no atrophy or inflammation or it may be superimposed on a pre-existing disorder. Diagnosis in the latter is impossible without continued observation and biopsy.

Treatment. The general approach to treatment should be similar to that for anal pruritus and any sort of vaginal discharge given the requisite treatment. Obviously, if diabetes is present, it must be controlled. Creams active against Candida such as nystatin are indicated if candidiasis is present. Any underlying cause of emotional tension should be discussed and anxiety and sleeplessness controlled by sedation. The changes of lichen sclerosus may persist for many years but some cases recover completely. Symptoms may be alleviated by topical steroids. Patients with lichen sclerosus must be kept under observation every 2 to 3 months since leucoplakia and malignant change may complicate the condition. Most authorities do not consider the risk is so great initially that vulvectomy is indicated but inability to relieve itching suggests that leucoplakia is more likely to occur ultimately. Once the diagnosis of true leucoplakia is established vulvectomy is indicated since carcinoma follows in 50 per cent of cases.