Approaching the pruritic patient

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Chapter 67 Approaching the pruritic patient

Theresa R. Pacheco, MD

1. What is the most common symptom of dermatologic disease?

Pruritus, or “itching.”

2. What is an “itch”?

It is an unpleasant sensation of the skin leading to the desire to scratch.

3. Is an itch a separate modality of pain or a submodality of pain?

Cutaneous nerve fibers arranged in an arborizing plexus immediately below the epidermis receive itch impulses. Unmyelinated C fibers conduct itch impulses from the skin to the ipsilateral dorsal root ganglia, ascend in the opposite anterolateral spinothalamic tract (closely associated with pain fibers), continue to the thalamus, and proceed through the internal capsule to the sensory cortex.

Although controversial, the general consensus views an itch as a separate modality of pain. Though distinguishing between the sensations of pain and pruritus is easy, distinguishing between the neurophysiology of pruritus and pain is not. Pruritus and pain share many neurophysiologic features and pathways. The following factors support that pain and itch are separate and distinct sensations: Itch leads to the reflex or urge to scratch; pain leads to withdrawal. Itch occurs only in the skin; pain arises from deeper structures as well. Heat may stop itch; heat usually increases pain. Removal of the epidermis eliminates itch; removal of the epidermis causes pain.

4. What causes an itch?

Itch is mediated by a number of local and central substances. Histamine, produced by skin mast cells, is the classical pruritus mediator. Pricking the skin with histamine produces pruritus in most individuals; however, histamine does not account for all pruritus. Other pruritus mediators include prostaglandin, serotonin, tachykinins, cytokines, and opioid receptors. Prostaglandin E₁ lowers the threshold of the skin to itching provoked by histamine. Serotonin, 5-hydroxytryptamine (5-HT), may regulate itch by acting on 5-HT₃ receptors. Tachykinins, such as the neuropeptide substance P, cause pruritus for reasons attributable to histamine release from mast cells. Cytokine interleukin-2 may be an important peripheral mediator of itching. Opioid receptors in the central nervous system regulate the intensity and quality of perceived itch.

Understanding pruritus mediators can help classify itch accordingly to origin. The classification of itch includes: a) pruritoceptive—cutaneous nerves are activated by pruritogens at sensory endings, b) neuropathic—diseased or lesion pruritic neurons generate itch, c) neurogenic—itch caused by mediators acting centrally, and d) psychogenic. Although classifications are important, there are limitations as itch can have more than one origin.

Bernard JD, editor: Itch: mechanisms and management of pruritus, New York, 1994, McGraw-Hill.

Buddenkotte J, Steinhoff M: Pathophysiology and therapy of pruritus in allergic and atopic diseases. Allergy 65:805-821, 2010.

Fazio SB: Pruritus, UpToDate 2000, 2005. Available at: http://www.uptodate.com.

Greaves MW, Wall PD: Pathophysiology of itching, Lancet 348:938–940, 1996.

5. Describe the difference between localized and generalized pruritus.

Pruritus occurs with a host of dermatologic conditions, or it can mark systemic disease. Some dermatologic conditions that cause pruritus are inconspicuous or nonspecific. Other dermatologic conditions are apparent on physical exam. A physician must differentiate between localized and generalized pruritus and know a variety of skin diseases that cause pruritus.

Localized pruritus is defined as itching focused to certain regions. Localized pruritus usually results from a regional infection or dermatosis. Generalized pruritus typically appears as itching that affects the entire body surface. It implies a dermatologic or systemic disorder. Generalized pruritus can be distinguished as acute or chronic. Chronic pruritus is defined as lasting 6 or more weeks.

6. What is the best approach to evaluation of a patient with localized pruritus?

The most important diagnostic tools are the history and physical exam. After obtaining a thorough history, the best clinical approach is to organize the patient regionally. The physician should ask the patient if there are any lesions associated with pruritus. The patient’s physical exam should focus on identifying a primary skin lesion or disorder in the affected region. After identifying a primary lesion, the physician can categorize the skin disease based on the lesion’s morphology.

7. What are the common causes of localized pruritus?

The differential diagnosis of localized pruritus should include dermatoses that are limited to certain parts of the body and those that are diffuse but have a predilection for these sites (Table 67-1).

8. What is notalgia paresthetica?

Notalgia paresthetica is an acquired unilateral localized form of pruritus that develops near the inferomedial border of either scapula. The skin typically appears normal, although some patients demonstrate subtle hyperpigmentation secondary to repeated rubbing or excoriation. The cause is not understood, although there is substantial evidence to suggest that it is due to spinal nerve impingement. Occasional cases have been familial, and the term “hereditary localized pruritus” has been applied to this variant. The management typically consists of topical capsaicin cream or topical preparations containing lidocaine.

Table 67-1. Differential Diagnosis of Localized Pruritus

LOCATION	DISEASES
Scalp	Psoriasis, seborrheic dermatitis
Trunk	Contact dermatitis (axillae, waistline), erythrasma (axillae), psoriasis (periumbilical), notalgia paresthetica, scabies, seborrheic dermatitis, urticaria
Inguinal region	Candida, contact dermatitis, erythrasma, overuse of topical steroids, pediculosis, scabies, tinea cruris
Anal region	Candida, contact dermatitis, gonorrhea, hemorrhoids, pinworm, psoriasis, tinea cruris
Hands	Contact dermatitis, scabies, eczema
Legs	Atopic dermatitis (popliteal fossae), dermatitis herpetiformis (knees), lichen simplex chronicus (malleoli), neurotic excoriations, nummular eczema, stasis dermatitis
Feet	Contact dermatitis, pitted keratolysis, tinea pedis

Savk O, Savk E: Investigation of spinal pathology in notalgia paresthetica, J Am Acad Dermatol 52:1085–1087, 2005.

9. What is the physician’s best approach when seeing a patient with generalized pruritus?

The physician’s most important diagnostic tools are a thorough and systematic history and physical exam. Laboratory testing for systemic disease may be necessary. Common questions include the following:

• What are the extent, severity, and quality of the itch?

• When does the pruritus occur, and what is its duration?

• Are there provocative factors, such as change in temperature or climate?

• Does the patient have a history of previous skin disorders or allergies?

• What are the patient’s current medications?

• Has the patient taken any new oral medications or ingested any new foods?

• How often does the patient bathe?

• What products does the patient use on his/her skin?

• Has the patient used any new skin products?

• Is there a history of systemic illness?

• Is health maintenance up to date?

• Is there a history of psychiatric illness?

• What is the home environment?

• Are there pets at home?

• Does any other family member experience itching?

• Has there been any recent travel?

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