Am Fam Physician. 2022;105(1):55-64
Patient information: See related handout on pruritus, written by the authors of this article.
Author disclosure: No relevant financial relationships.
Pruritus is the sensation of itching; it can be caused by dermatologic and systemic conditions. An exposure history may reveal symptom triggers. A thorough skin examination, including visualization of the finger webs, anogenital region, nails, and scalp, is essential. Primary skin lesions indicate diseased skin, and secondary lesions are reactive and result from skin manipulation, such as scratching. An initial evaluation for systemic causes may include a complete blood count with differential, creatinine and blood urea nitrogen levels, liver function tests, iron studies, fasting glucose or A1C level, and a thyroid-stimulating hormone test. Additional testing, including erythrocyte sedimentation rate, HIV screening, hepatitis serologies, and chest radiography, may also be appropriate based on the history and physical examination. In the absence of primary skin lesions, physicians should consider evaluation for malignancy in older patients with chronic generalized pruritus. General management includes trigger avoidance, liberal emollient use, limiting water exposure, and administration of oral antihistamines and topical corticosteroids. If the evaluation for multiple etiologies of pruritus is ambiguous, clinicians may consider psychogenic etiologies and consultation with a specialist.
Pruritus is the sensation of itching. Although large-scale epidemiologic data on prevalence are limited, pruritus is a common symptom encountered in primary care.1,2 The etiology of pruritus is complex and can include histamine, serotonin, and neuropeptide release, and neuronal itch signal transmission.1 Risk factors include older age, known or new dermatologic disease, and systemic conditions, such as renal and hepatic disease.1 When inadequately treated, pruritus can adversely affect a patient's quality of life by altering mood, stress levels, and sleep.3
Differential Diagnosis
The differential diagnosis of pruritus is broad and includes acute and chronic (i.e., at least six weeks of symptoms) presentations.1,2 Primary and secondary skin lesions suggest dermatologic etiologies of pruritus (Table 14). When distinct exposures result in symptoms, the underlying etiology is often discovered. However, the absence of obvious triggers or examination findings coupled with chronic symptoms makes identifying the underlying etiology of pruritus more challenging.
| Etiology | Features |
|---|---|
| Allergic or irritant contact dermatitis | Bullae, vesicles, erythema, and edema localized to area in contact with exposure Reaction within days of exposure |
| Atopic dermatitis | Erythematous papules, patches, or plaques; pruritic area where rash appears when scratched in patients with atopic conditions (e.g., allergic rhinitis, asthma) Involvement of crease areas (axillae, wrists, ankles, popliteal and antecubital fossae) Chronic, worsens with itch-scratch cycle |
| Bullous pemphigoid | Initially pruritic urticarial lesions, often in intertriginous areas Formation of tense blisters |
| Cutaneous T-cell lymphoma (mycosis fungoides) | Oval eczematous patch on skin with no sun exposure (e.g., buttocks) Possible presentation of new eczematous dermatitis in older adults Possible presentation of erythroderma |
| Dermatitis herpetiformis | Rare vesicular dermatitis affecting the lumbosacral spine, elbows, or knees |
| Dermatophyte infection | Can occur on several sites, including the feet, trunk, groin, scalp, and nails Localized pruritus and rash characterized by peripheral scaling and central clearing Patchy alopecia on scalp Dystrophic or discolored nails |
| Folliculitis | Pruritus out of proportion to appearance of dermatitis Papules and pustules at follicular sites on chest, back, or thigh |
| Lichen planus | Lesions often located on the flexor wrists Characterized by the six P's (pruritus, polygonal, planar, purple, papules, plaques) |
| Lichen simplex chronicus | Localized, intense pruritus Initial erythematous, well-defined plaques with excoriations lead to thickened, lichenified, violaceous patches if scratching continues |
| Pediculosis (lice infestation) | Adult organisms and nits on hair shafts Occiput in school-aged children; genitalia in adults (sexually transmitted) |
| Psoriasis | Plaques on extensor extremities, low back, palms, soles, and scalp |
| Scabies | Burrows, vesicles, and papules in finger web spaces and axillae and on wrists, ankles, genitals, and extensor surfaces Pruritus worse at night Can persist after mite eradication |
| Sunburn | Possible photosensitizing cause (e.g., with use of nonsteroidal anti-inflammatory drugs or cosmetics) |
| Urticaria (hives) | Intensely pruritic, well-circumscribed, erythematous, and elevated wheals Lesions are transient, may coalesce, and wax and wane over several hours |
| Xerosis | Intense pruritus, often during winter months in northern climates Involvement of back, flank, abdomen, waist, and lower extremities More common in older people |
The International Forum for the Study of Itch has proposed a formal classification system for chronic pruritus with three different clinical classes: pruritus on diseased skin (Group I), pruritus on nondiseased skin (Group II), and chronic reactive lesions acquired from skin manipulation, such as rubbing, picking, or scratching (Group III).5 Group I presentations suggest a dermatologic etiology. Group II presentations suggest systemic, neurogenic, or psychogenic etiologies. Group III presentations may result from any one of the previously mentioned etiologies or a mixed presentation. The classification also includes chronic pruritus of unknown origin, for which there are no known effective interventions.6 Pathognomonic skin findings and the extent of bodily involvement can also suggest certain diagnoses (Figure 17).
Common Dermatologic Etiologies of Pruritus
ATOPIC DERMATITIS
Atopic dermatitis is an inflammatory skin condition that is often associated with secondary lesions that result from scratching or other skin manipulation findings, such as excoriations, lichenification, and hyperpigmented or erythematous papules or plaques (Figure 2). Patients scratch pruritic areas and subsequently develop secondary lesions, worsening dermatitis and associated pruritus; this process is often called the itch-scratch cycle. Flexural areas are commonly affected, including ankles, regions behind the ears, and the antecubital and popliteal fossae. Patients with this condition often have a personal or family history of asthma or allergic rhinitis, and symptoms commonly begin during childhood. Treatment includes limiting exposure to water, liberal emollient use, and topical corticosteroid application.8,9
CONTACT DERMATITIS
Contact dermatitis is an inflammatory reaction that typically erupts within days of direct skin contact with an environmental trigger. Associated primary skin findings include bullae, vesicles, erythema, and edema, localized to areas that directly contacted the trigger. Irritant and allergic mechanisms are common. Irritant contact dermatitis is not immunologically mediated and progressively compromises the physical and chemical composition of the epidermis. In contrast, allergic contact dermatitis is dependent on a delayed hypersensitivity reaction and is more common in people with atopy. Contact dermatitis treatment includes avoidance of triggers, such as rough textiles, detergents, perfumes, chemicals, and dyes,1,4,10 and topical corticosteroid application.11
DERMATOPHYTOSIS
Tinea infections are caused by fungi that can survive only on dead keratin, including the most superficial layer of the epidermis (i.e., stratum corneum), hair, and nails. The characteristic ringworm rash appears as a well-demarcated region with a red, scaly, elevated border containing the highest concentration of fungal hyphae. Tinea pedis more often affects toe webs and soles of the feet, and the skin can become dry, scaly, fissured, or soft and macerated. Tinea capitis may present with patchy alopecia and scaling of the scalp. Onychomycosis is associated with dystrophic, discolored nails. Direct visualization of fungal hyphae on scale scrapings, hair shafts, and nail clippings prepared with potassium hydroxide solution aids in the diagnosis. Treatment includes topical and oral antifungals.12
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