Lichenoid Disorders

‘Lichenoid’ can describe the appearance clinically of a shiny flat-topped papular rash or can suggest histology of band-like inflammatory cell infiltrate in the upper dermis with basal cell necrosis. Lichenoid eruptions can be due to a number of causes including lichen planus (LP), drug eruptions, graft versus host disease (GvHD) and pityriasis lichenoides (Table 15.1).

Lichen Planus

Most people with cutaneous LP (>70%) have oral involvement; 10% present with this. LP is a T-cell mediated autoimmune inflammatory condition. There are possible genetic links and association with hepatitis C. LP presents as shiny, flat topped, violaceous polygonal papules on the skin (Figure 15.1). Papules vary in size and many clinical patterns are seen (Table 15.2). In typical presentations, with distribution on the dorsum of the ankles and wrists, a biopsy is not always required; however, LP can occur on any body site including the palms and soles.

Wickham’s striae describes the surface white lines with a lace-like pattern (Figure 15.2). Hypertrophy and hyperpigmentation in darker skin types is common and linear lesions can occur along scratch marks or scars (Koebner’s phenomenon) (Table 15.3). Itching is common but can be absent.

Mucosal areas (60%) in the mouth may cause pain and ulceration (Figure 15.3). Mucous membrane involvement may need patch testing to exclude allergy (e.g. mercury amalgam). The nails are affected (10%) with ridging (Figure 15.1d) and thinning of the nail plate and pterygium (adhesions between the posterior nailfold and nail plate). Scarring alopecia on the scalp with skin atrophy can cause permanent scarring.

Histopathology

Typical features are an irregular saw tooth thickening of the epidermis (acanthosis) with Civatte bodies (necrotic basal epidermal cells) and a lymphocytic inflammatory infiltrate (Figure 15.4). Specific features are seen in hypertrophic, atrophic, follicular and mucosal lichen planus. Differential diagnoses include plane warts, eczema and pityriasis rosea, and lichen simplex chronicus.

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