Friday, 19 August 2016
Friday, 12 August 2016
Dermographism (writing on the skin) is an exaggerated wealing tendency when the skin is stroked. It is the most common form of inducible urticaria, followed by cholinergic urticaria. More than one form of inducible urticaria may occur in the same patient.
The triple response* of capillary vasodilatation (initial red line), surrounding flare due to axon reflex‐induced dilatation of arterioles and weal (increased permeability of the capillaries and postcapillary venules, with consequent extravasation of fluid and oedema), after stroking the skin was first described by Lewis and it occurs in normal people. Histamine is known to be a principal mediator of the triple response of Lewis, and to act via H 1 and H 2 receptors to produce vasodilatation and increased vascular permeability. Neuropeptides contribute to the reaction. The reaction does not occur in chronically denervated skin, or in skin in which neuropeptides have been depleted by capsaicin. In 2–5% of the population, this response is exaggerated enough to be called dermographism. It occurs in seconds to minutes after the skin has been stroked. It is most easily diagnosed by using a calibrated instrument, the dermographometer, which has a spring-loaded stylus, the pressure of which can be adjusted to a predetermined setting. Stroking the skin at a tip pressure of less than 36 g/mm 2 induces a linear itching weal within 10 min. The amount of vasodilatation can be measured by a Doppler flow meter.
In delayed dermographism, a delay of several hours from the physical stimulus occurs before dermographism appears. After normal fading of the triple response (or after an immediate dermographic response), a weal returns in the same site, but is usually tender and persists for up to 48 hours. It is closely related to pressure urticaria in which a delayed dermographic response is not unusual.
In red dermographism, repeated rubbing is necessary to induce small punctate weals.
When accompanied by severe itching dermographism is called symptomatic dermographism (a minority of those showing dermographism) . Symptomatic dermographism can occur at any age, but the greatest incidence is in young adults. Patients complain of wealing and marked itching at sites of trauma, friction with clothing or scratching the skin. The itching is usually disproportionately severe compared with wealing and is often most severe at night. The eliciting stimulus determines the shape of the weals but they are often linear from scratching or stroking.
Dermographism is usually idiopathic. It may last for months or years, or be present intermittently. It may be associated with other forms of inducible urticaria. It may be present in chronic spontaneous urticaria. It may sometimes follow a drug or an infestation. It may occur in hypothyroidism and hyperthyroidism, infectious diseases, diabetes mellitus, and during onset of menopause. It may be a cause of localized or generalized pruritus. Localized symptomatic dermographism is a relatively common cause of urticaria to gloves in the absence of latex allergy. Dermographism of clinically uninvolved skin is present in one third to one half of urticaria pigmentosa patients. Dermographism is a feature of Sjögren–Larsson syndrome. In genital pruritus, it is useful to elicit dermographism of the inner thighs because such patients may be helped by oral antihistamine treatment. Dermographism may be associated with raised linear bands of infancy.
Cholinergic dermographism is seen in some patients with cholinergic urticaria, whose dermographic response consists of an erythematous line studded with punctate weals characteristic of cholinergic weals.
Pallor (blanching) of the skin after stroking is called white dermographism. This reaction differs from the classic dermographism, in that it typically lacks a weal, and flaring is replaced by blanching to produce a white line. Typically seen in lesions of atopic eczema patients since the small blood vessels in these patients show a tendency to capillary vasoconstriction responses (different signalling but this does not mean that histamine is not increased). It becomes more evident with the chronicity of the disease but is absent following treatment. It should be noted however that white dermographism occurs normally following light stroking of the skin but it is particularly pronounced in atopic eczema.
Black (or greenish) dermographism is discoloration of the skin after pressure from a metallic object.
Other forms of true and false dermographism (not all forms of dermographism are urticaria) have been described.
Treatment of symptomatic immediate dermographism with low‐sedating H1 antihistamines is often effective, but some patients do not respond. The addition of an H2 antihistamine may be of benefit but it should be noted that dermograhism has been reported to be associated with the use of the H2 blocker famotidine. Sedating antihistamines such as hydroxyzine can be helpful. Treatment may need to be continued regularly for at least several months; intermittent therapy is of less value. Omalizumab has been successfully used in patients with physical urticaria, including symptomatic dermographism. Resistant cases may find narrow band UVB phototherapy helpful.
*Ganong's Review of Medical Physiology: When a pointed object is drawn lightly over the skin, the stroke lines become pale (white reaction). The mechanical stimulus apparently initiates contraction of the precapillary sphincters, and blood drains out of the capillaries and small veins. The response appears in about 15 seconds. When the skin is stroked more firmly with a pointed instrument, instead of the white reaction there is reddening at the site that appears in about 10 seconds (red reaction). This is followed in a few minutes by local swelling and diffuse, mottled reddening around the injury. The initial redness is due to capillary dilatation, a direct response of the capillaries to pressure. The swelling (weal) is local oedema due to increased permeability of the capillaries and postcapillary venules, with consequent extravasation of fluid. The redness spreading out from the injury (flare) is due to arteriolar dilatation. This three-part response—the red reaction, weal, and flare—is called the triple response and is part of the normal reaction to injury. It is due to an axon reflex, a response in which impulses initiated in sensory nerves by the injury are relayed antidromically down other branches of the sensory nerve fibres. This is the one situation in the body in which there is substantial evidence for a physiologic effect due to antidromic conduction.
The page was last updated in August 2016.
Tuesday, 2 August 2016
Berloque (a pendant) dermatitis is skin pigmentation due to phototoxic reaction to perfumes applied to the skin. Berloque dermatitis is considered a special form of phytophotodermatitis.
The reaction occurs commonly on the neck (hence the name berloque) and face. The acute inflammatory dermatitis due to berloque dermatitis might be unnoticed thus the patient presents with the streaky pigmentation. If the inflammatory phase is severe, bullae are formed. The distribution of the lesions is variable (and here it is on the upper limb) but their configuration is usually distinctive. Deep‐brown pigmentation follows the pattern formed by the trickle of the droplets of perfume over the skin from their points of application.
Berloque dermatitis results from the potentiating of UV‐stimulated melanogenesis by 5‐methoxypsoralen (bergapten) in perfumes containing bergamot oil. If a fragrance containing this 5-methoxypsoralen (or another furocoumarin) is applied to the skin before exposure to the sun or tanning lights, berloque dermatitis may result. There are guidelines limiting the use of furocoumarins in some places. There is wide variation in susceptibility. This variation depends on the readiness with which the bergapten is absorbed, the quantity applied, and the intensity and duration of exposure to UV light. Susceptibility is increased by stripping the horny layer. Hot humid conditions favour absorption. The pigmentation occurs in susceptible subjects who have been exposed to light after the application of perfume. Some regulations restrict the concentration of bergapten so that it is below the threshold required to cause dermatitis/pigmentation.
The reaction fades gradually over weeks to months. Sunscreens protect the skin from further sun exposure. If tinted, they can also disguise the lesions.
The child used to apply her mother’s perfume on the left upper limb.
This page was last updated in August 2016.
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Making Clinical Decisions and Prescribing
Main Works of Reference List (The first eight are my top favourites)
- British National Formulary
- British National Formulary for Children
- Guidelines (BAD - BASHH - BHIVA - Uroweb)
- Oxford Handbook of Genitourinary Medicine, HIV, and Sexual Health
- Oxford Handbook of Medical Dermatology
- Rook's Textbook of Dermatology
- Simple Skin Surgery
- Weedon's Skin Pathology
- A Concise Atlas of Dermatopathology (P Mckee)
- Ackerman's Resolving Quandaries in Dermatology, Pathology and Dermatopathology
- Andrews' Diseases of the Skin
- Andrology (Nieschlag E FRCP, Behre M and Nieschlag S)
- Bailey and Love's Short Practice of Surgery
- Davidson's Essentials of Medicine
- Davidson's Principles and Practice of Medicine
- Fitzpatrick's Colour Atlas and Synopsis of Clinical Dermatology (Klaus Wolff FRCP and Richard Allen Johnson)
- Fitzpatrick’s Dermatology in General Medicine
- Ganong's Review of Medical Physiology
- Gray's Anatomy
- Hamilton Bailey's Demonstrations of Physical Signs in Clinical Surgery
- Hutchison's Clinical Methods
- Lever's Histopathology of the Skin
- Lever's Histopathology of the Skin (Atlas and Synopsis)
- Macleod's Clinical Examination
- Martindale: The Complete Drug Reference
- Oxford Handbook of Clinical Examination and Practical Skills
- Oxford Textbook of Medicine
- Practical Dermatopathology (R Rapini)
- Sexually Transmitted Diseases (Holmes K et al)
- Statistics in Clinical Practice (D Coggon FRCP)
- Stockley's Drug Interactions
- Treatment of Skin Disease: Comprehensive Therapeutic Strategies
- Yen & Jaffe's Reproductive Endocrinology
Selected Free Access Websites
- Andrology Guidelines
- Atlas (Australian - Dermoscopy)
- Atlas (New Zealand Dermatological Society)
- Dermatology (British Guidelines)
- Dermatology (Cosmetic Procedures Videos)
- Dermatology (Dermatopathology Discussion)
- Dermatology (E-learning Sessions)
- Dermatology (Hair Transplants Videos)
- Dermatology (Patient Information Leaflets)
- Egyptian Doctors
- Ethical and Legal Issues (Medical Protection Society)
- Good Medical Practice (General Medical Council)
- Journal Watch - Hong Kong Journal of Dermatology and Venereology
- MCQs (MRCP - Question of the Day)
- MCQs (MRCP)
- Medicine (Manual of Diagnosis and Therapy)
- Medicine Notebook
- National Health Service (NHS) Videos
- Resuscitation Council (UK) Videos
- Royal Colleges of Physicians (Glasgow, Edinburgh and London) Videos
- Royal Society of Medicine (RSM) Videos
- Venereology (E-Learning Session)
- Venereology (E-Learning Sessions Extra)
- Venereology - HIV Medicine (British Guidelines)
- Venereology - STI (British Guidelines and Patient Information Leaflets)
- Venereology - Sexual Dysfunction (British Guidelines)