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Internal and Esternal Causes of the Condition
This general term includes many varieties of the same condition, its causes being equally varied In these pages pruritus is classified by the causes, and a list is given showing the steps by which diagnosis, which is always difficult in this conditiong is achieved. The condition is often intractable, but possible treatments are suggested.
The term pruritus is applied to itching in general, including tingling and burning, special types being differentiated by a distinguishing adjective.
External Causes
Causes of itching may be either internal or external. The commonest examples of the external type occur in the animal and vegetable kingdoms. No special susceptibility would seem to be necessary, and everybody bitten by a mosquito, gnat, horsefly, flea, bed-bug, harvest-bug, etc., suffers from the symptom in a greater or less degree. Of special importance in this category, because of their contagious properties, are the acarus (or mite) of scabies, known also as the itch, and the body and the head louse. These are discussed under their appropriate headings.
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In the plant world it is only necessary to refer to the stinging-nettle, while under this heading may be mentioned ringworm, a large group of itching eruptions due to the growth in the upper layers of the skin of certain pathological fungi allied to the moulds.
Besides these causes of itching, which are more or less common to the human species, there is a large group of irritants whose power is chiefly demonstrable in susceptible individuals. They include dusts and liquids used or given off as by-products in many trades, e.g. bakers (flour), washerwomen (soda and alkaline soaps), French polishers (turpentine), grocers (sugar). They are dealt with in general under the headings Dermatitis and Eczema. These trade eczemas of itching type are not universal, and occur mostly in persons with an idiosyncrasy to a particular irritant. The same may be said of certain drugs used as local applications, e.g. iodoform, mercury, picric acid, belladonna, silver, nitrate, turpentine and sulphur, which is so commonly used in an ointment for scabies. Most of such cases are associated with a more or less typical rash.
Almost any external stimulus of a chemical nature, if long enough applied, or if the subject happens to be a susceptible person, may produce pruritus. Such are the eruptions, always associated with severe itching, which occur as the result of exposure to sunlight. These are limited to uncovered parts of the body, and occur with special frequency in the spring and summer months. The susceptibility may be either inherited or acquired. In the latter case a careful investigation sometimes reveals some intestinal or urinary abnormality or infection. The bacteria produce a number of toxic amines which when secreted in the sweat produce itching.
Another example of pruritus, due to an idiosyncrasy, is that produced by the action of certain plants. In most cases there is a history of contact with the leaves or flowers, but there is evidence to show that actual handling is not essential, and that the symptom may be produced by the scent or odourless exhalations from Chinese primula, poison oak, chrysanthemums and a number of other plants to which certain individuals have developed an acute and delicate sensibility. This type of reaction is strictly comparable to the effects of certain grass-pollens in producing hay fever by allergic reaction.
The tendency or inclination of an individual to suffer from pruritus may be due to an inherited abnormality of the skin structure. Some persons are born with too dry a skin (xeroderma). There is a deficiency of the oil and sweat glands in such individuals, and the drying effects of sun and wind are not properly counteracted. It is not surprising to find that itching and eczematous sequelae, such as fissuring and moist patches, are frequently complained of by such patients, who can only protect themselves in cold weather by the application of grease or lotion.
Internal Causes
Internal causes of itching are less easily explained. The actual poisons which are conveyed by the blood or lymph to the skin., and which may there produce the sensation of itching. The simplest example is that of nettle-rash, which is the lay term for urticaria. In this often intractable complaint the patient may be a susceptible subject, i.e. he is unable to digest properly the proteins of shellfish, salmon, strawberries, wheat or oats, with the result that certain substances are absorbed into the circulation from the stomach and produce symptoms of irritation, itching, burning or tingling in the skin, sometimes with and sometimes without a characteristic eruption.
There are certain recognizable blood diseases which can be microscopically classified, in which itching of the skin is a pronounced symptom. In not a few cases of general itching, without eruption the cause may be a septic one. Abscesses at the roots of the teeth, septic tonsils and other visible foci of infection have been proved causal.
Excess of sugar in the blood, as in diabetes and glycosuria, is a common cause of pruritus.
Diseases of the liver and kidneys sometimes attract notice for the first time by developing the symptom, and cases of jaundice (a liver disorder) associated with intense general irritation of the skin are common. Certain nervous diseases (locomotor ataxia, hysteria, epilepsy and tumours of the brain) are occasionally produetive of intractable itching.
No such case should escape an examination of the teeth, by X-rays if necessary, of the blood, and urine, while if these all fail to give a positive result there are available certain tests which indicate efficiency of the kidney and liver funtions.
In many textbooks there is described a form of pruritus associated with a wasted type of skin in old persons. The name of senile pruritus has been given to this variety, but true examples of it are rare, and most of the cases can be benefited by attention to one or other of the internal causes of pruritus.
Complications of Pruritus.
Patients with prolonged itching are liable to complications attributable directly and indirectly to the symptom. Nearly every case is worse at night, thus inevitably disturbing sleep and causing severe disturbance of the nervous system.
Besides the effects on the general health, the constant scratching may initiate attacks of boils, which are a very common complication after the sulphur treatment of scabies. Occasionally there may be chronic lichenified patches on the fronts of the thighs or the back of the neck which remain and continue to itch long after the main trouble has subsided.
In the foregoing account the causes of pruritus have been reviewed at some length, for a knowledge of these is all-important in the treatment and cure of the symptom. It should be remembered that itching is not a disease, but only a symptom of some pathological state, which may be either local (e.g. parasitic, chemical, etc.) or of less obvious internal causation, like an infected tooth. It should also by remembered that most skin diseases exhibit the tendency to itch at some period or other of their course, e.g. eczema, lichen planus, psoriasis.
Diagnosis and Treatment
The following routine should be performed in every case: Examination of the patient and his clothing
for evidence of parasites. The patient must be stripped and the whole body, especially the hairy regions, examined in a good light.
Examination of the urine for albumin, sugar, bile, etc. Examination of the blood by a skilled pathologist.
The history must be carefully investigated for evidence of a special susceptibility to certain foods, drugs, plants, etc. A seasonal recucrence of the symptom would suggest the influence of light, pollen, or foods such as strawberries, lobster etc., which can only act at definite periods of the year.
Examination for foci of chronic infection in the teeth, tonsils, intestines and other areas where bacteria may flourish undetected.
Examination of the nervous system for signs of organic nerve disease, such as locomotor ataxia, cerebral tumour, etc.
When there is a well-defined type of eruption it may be assumed that the pruritus is a symptom of this, and that its alleviation depends upon a cure of the rash.
Treatment with Cause Unknown
Unless one of the above causes can be detected the chances of cure are small. Treatment is then reduced to the local application of medicaments in baths, lotions or ointments, which act purely as local sedatives and cannot be expected to affect the cause and the administration of general sedatives such as bromides aspirin or salicylic acid by the mouth. The elimination of all fluids and foodstuffs with a heating or irritating effect, such as alcohol, coffee and condiments, is essential; daily action of the bowels and the free secretion of the urine must be procured. Baths are given tepid, and may contain bran or oatmeal in a proportion of 2 lb. to 30 gallons of water. The patient must not stay in a bath longer than ten to fifteen minutes. A lotion containing aloe vera with coconut milk is very soothing, and not too desiccating.
If the skin is dry, cold cream may be freely applied. Medicaments should not be added by any but medical men. A simple non-medicated dusting powder is useful in all cases, and attention should be paid to the thickness and quality of the underwear, which, if coarse and non-porous, may aggravate the trouble.
In ordering aperients for the free flow of the bowels, cascara, aloes and other vegetable laxatives should give place to mild saline laxatives. Regular exercise in the fresh air should be insisted on, and spa treatment, if the patient's means allow, is sure to do good. There are no reliable drugs.
Local Pruritus
There are certain parts of the body, wherc cavities comnnmicate with the exterior (muco-cubaneous junctions), which seem particularly prone to be affected by pruritus, which is then known as local pruritus. The rectum in men and the vulva in women are very commonly the sites of intractable itching. The patients are usually middle-aged and of sedentary habits. The itching is mostly of paroxysmal type, and may come on suddenly at any time, though mostly at night, when it disturbs sleep.
The causes of pruritus ani, which is considered under the heading Anus, must in every case be investigated by a local examination. If piles, fissures, abrasions and fistulae are not evident, an inquiry for constipation, the presence of threadworms (for which the stool may have to be microscopically examined) or a history of dysentery must be made. If the local examination prove negative, the urine must be examined for sugar or albumin, and evidence of liver disturbance due to alcohol or other irritant carefully sought.
In a large number of cases both of pruritus ani and pruritus vulvae there is no evidence of any local cause for the itching, and repeated examinations for pathological conditions of the urine and faeces may also prove negative. The causation may then be regarded as of obscure nervous origin.
Local pruritus, when it occurs without an obvious external cause, is often associated with nervous instability. Of this type is the patch of grained and thickened dermatitis (lichenification) which is apt to occur on the nape of the neck in women. These patients may suffer from the symptoms for years, and doubtless keep it up by friction and rubbing, which temporarily relieve it. So suggestive of a nervous cause are these cases that the name neuro-dermatitis is frequently given to them.
Other areas in which unexplained itching may give rise to trouble are the palms and soles. It seems to occur in persons with a dry skin especially, and may also affect the gouty subject. In the auditory canal the ocenrrence of itching is generally the result of wax, while in the nose it may, if the subject be a child; be a symptom of threadworms.
In the urethral orifice pruritus is usually the result of gonorrhoea, or an early symptom of it, and may spread from there to the scrotum, vulva or vagina. Diabetes and cystitis may also be responsible. Localised patches of lichenification may remain as relics of a more or less generalised eczema or dermatitis due to an external or internal cause. The tendency would seem to be a characteristic type of reaction, and peculiar to the individual, for it does not result from scratching in all who suffer from pruritus.
A form of eczema and dermatitis found on the wrists and hands of grocers, which is acquired chiefly from contact with sugar, is called grocer's itch. Its symptoms and appearance are similar to other forms of eczema and the treatment is the same.