LICHEN NITIDUS

 LICHEN NITIDUS:

 Lichen nitidus is a rarer condition than idiopathic LP and is clinicallycharacterized by the presence of pinpoint to pinhead-sized papules, which are usually asymptomatic, fl esh coloured, with a
fl at, shiny surface. 

Aetiology:  Early, tiny Lichen Planus(LP) papules may be clinically and histopathologically indistinguishable from lichen nitidus . Immunophenotypic studies also reinforce the association
between LP and lichen nitidus . However, some authorities favour a separation into two dermatoses, because of histopathological differences, or differences in cytokine expression in lichen nitidus. Surprisingly, direct IMF studies in lichen nitidus have given negative results . However, ultrastructural studies have shown identical changes in lichen nitidus and LP.

 Histology. The histology of a typical papule is characteristic. The papule is formed by an intense infi ltrate situated immediately below the epidermis and is well circumscribed. The infiltrate consists
of lymphocytes and histiocytes and there are often a few Langhans’ giant cells , plasma cells.  The overlying epidermis is flattened and sometimes there is liquefaction degeneration of the basal cell
layer. The rete ridges at the margin of the infi ltrate are elongated and tend to encircle it. Although tuberculoid in appearance, there is never true tubercle formation or caseation. The histology of a
palmar lesion may show a deep parakeratotic plug, which distinguishes it from the palmar lesions of LP . Perifollicular granulomas can occur in spinous and follicular lichen nitidus, which
may simulate lichen scrofulosorum .

Incidence. In its characteristic monomorphic form, lichen nitidus is rare, but lesions of lichen nitidus occurring in association with LP are more common .

Age: Most cases occur in children or young adults.

Clinical features. Typical lichen nitidus papules are minute, pinpoint to pinhead sized, and have a fl at or dome-shaped, shiny surface. They usually remain discrete, although they may be closely grouped . They are found on any part of the body but the sites of predilection are the forearms, penis , abdomen, chest and buttocks. The eruption is sometimes generalized .  On the palms, the minute papules can become purpuric  and may occasionally resemble pompholyx Such cases may lack lesions of lichen nitidus elsewhere, so a biopsy is essential to confi rm the diagnosis . Linear lichen nitidus has been described, but is exceptionally rare . Nail pitting may coexist with
lichen nitidus or the affected nails may appear rough due to increased linear striations and longitudinal ridging . Mucous membrane lesions occur occasionally and are much rarer than in LP.

Lichen nitidus has been described in association with Crohn’s disease , trisomy 21 and congenital megacolon .

Treatment. As the disease is often asymptomatic and eventually self-limiting, no treatment is required in most cases, but fl uorinated topical steroid preparations may be recommended if treatment
is demanded, for example for lesions on the penis, and can be dramatically successful . Clearance of generalized lichen nitidus has been described with sun exposure , PUVA  ornarrow-band UVB phototherapy , and astemizole. Acitretin can lead to a gradual improvement in palmoplantar
lichen nitidus.


Source: Rook textbook of Dermatology.