What tests are used to diagnose neurodermatitis?

Diagnosis of Neurodermatitis

Neurodermatitis (lichen simplex chronicus) is diagnosed clinically based on the characteristic appearance of lichenified plaques in typical locations, without requiring laboratory investigations in most cases. 1

Clinical Diagnosis

The diagnosis relies entirely on clinical assessment, as laboratory tests are rarely helpful for this condition. 2

Key Clinical Features to Identify

• Lichenified plaques: Thickened, leathery skin with exaggerated skin markings resulting from chronic scratching 1, 3
• Typical locations: Commonly bilateral on elbows and knees, but can occur on extremities, neck, scalp, or anogenital areas 3
• Severe pruritus: Intense itching that drives the itch-scratch cycle, often worse in evening, while resting, or in hot environments 3
• Sharp, well-demarcated borders: Plaques are typically smaller and sharper than other lichenified conditions 3
• Keratotic surface: More prominent scaling and keratosis compared to other chronic dermatoses 3

Patient History Elements

Take a detailed history focusing on: 2

• Duration and progression of symptoms
• Pruritus patterns and triggers
• Previous treatments attempted and their effectiveness
• Psychosocial stressors (psychic factors trigger or exacerbate neurodermatitis in approximately 30% of cases) 4
• Medication history, particularly NSAIDs, beta-blockers, and lithium, which can worsen pruritus 1

Differential Diagnosis Testing

Patch testing should be considered when allergic contact dermatitis cannot be excluded clinically, particularly in chronic or persistent cases unresponsive to standard therapy. 2

When to Perform Patch Testing

Offer patch testing with a baseline allergen series in these scenarios: 2

• Disease aggravated by topical medications or emollients
• Unusual distribution patterns (e.g., sides of feet, marked facial/eyelid involvement)
• Later onset or new significant worsening of disease
• Persistent/recalcitrant disease not responding to standard therapies
• Vesicular lesions on dorsal hands and fingertips

Patch testing technique: 2

• Apply suspected allergens to unaffected skin (typically the back) for 48 hours
• Read reactions at time of patch removal and again at day 4
• Consider additional readings at day 6 or 7 if results are unexpectedly negative at day 4 2
• Sensitivity ranges from 60-80% 2

Timing Considerations for Patch Testing

Defer patch testing when possible: 2

• 6 weeks after natural or artificial UV exposure
• 3 months after finishing systemic immunosuppressive agents
• 6 months after finishing biological agents

This minimizes false-negative reactions, though testing can proceed if immunosuppression cannot be safely stopped. 2

Distinguishing from Psoriasis

Psoriasis can be differentiated from neurodermatitis by the presence of silvery scale, involvement of extensor surfaces, nail changes, and less severe pruritus. 1

Key distinguishing features: 2, 1

• Psoriasis: Silvery scale, extensor predominance, nail pitting/onycholysis, less itchy
• Neurodermatitis: Lichenification, intense pruritus, no nail changes, no silvery scale

Note that "psoriatic neurodermatitis" may represent itchy psoriasis superimposed with lichen simplex chronicus, showing features of both conditions. 3

Skin Biopsy

Skin biopsy is not routinely required but may be performed when the diagnosis is uncertain or to exclude other conditions. 2

Histopathological features of neurodermatitis include: 3

• Hypergranulosis (unlike psoriasis which shows hypogranulosis)
• Irregular acanthosis
• Thickening of suprapapillary plates
• Absence of microabscesses in the horny layer (present in psoriasis)

A second biopsy from perilesional skin should be sent for direct immunofluorescence if immunobullous disorders are in the differential. 2

Clinical Assessment Tools

Use standardized assessment tools for both initial evaluation and monitoring treatment response: 2

• Dermatology Life Quality Index (DLQI): Generic quality of life measure
• Hand Eczema Severity Index: For hand involvement
• Body mapping: Document extent and location of lesions

Common Pitfalls to Avoid

• Do not rely on laboratory investigations as they are rarely helpful in diagnosing neurodermatitis 2
• Do not perform routine allergy testing (prick tests, Phadiatop) unless specific triggers are suspected, as these show no significant differences between neurodermatitis and other conditions 3, 4
• Do not overlook psychiatric comorbidities, particularly depressive disorders which occur more frequently in patients with neurodermatitis 3
• Do not ignore the itch-scratch cycle as breaking this cycle is essential for successful treatment 1