Diagnosis: Hypertrophic lichen planus
Hypertrophic lichen planus (HLP), a variant of lichen planus (LP), is a lesion that is usually found on the distal extremities. HLP plaques evolve from initial characteristic LP lesions (purple, planar, pruritic, polygonal papules or plaque) to form reddish-brown to violaceous, hypertrophic, verrucous round-to-elongated plaques. Primary lesions may be spread by scratching or other trauma and often develop dark brown hyperpigmentation over several years. Like other variants of LP, HLP most commonly affects adults 30 to 60 years of age, with a slight female predominance.1
HLP may be idiopathic, drug induced, or associated with a systemic disease. Although many drugs have been linked to this lesion, the most commonly reported medications are gold salts, beta-blockers, antimalarials, thiazides, furosemide, and penicillamines. If your patient has HLP and is taking one of these medications, you should consider discontinuing the medication.1 As with other forms of LP, HLP has been associated with hepatitis C. Consider transaminases and a hepatitis panel for all patients with HLP. Other HLP-associated conditions include venous insufficiency, herpes simplex virus, and varicella-zoster virus.1
When the history confuses the diagnosis
When there are surrounding classic LP lesions, the diagnosis of HLP is fairly straightforward. However, when the patient has a history of surgery or trauma preceding the lesions and no surrounding classic LP lesions, the diagnosis may be less clear-cut. In such cases, the differential diagnosis includes lichen simplex chronicus, mycetoma, chromoblastomycosis, and squamous cell carcinoma.
Lichen simplex chronicus can be distinguished from HLP by reviewing the patient’s history. Patients who describe habitual rubbing or scratching of the area are likely to have lichen simplex chronicus. On exam, lichen simplex chronicus lesions are slightly erythematous, scaly, well-demarcated, and firm. There are rough plaques with exaggerated skin lines (lichenification) rather than the verrucous surface typically seen with HLP lesions. Wickham’s striae (seen in LP) are not seen with lichen simplex chronicus, and the lesions are localized only to easily reached areas.2
Mycetoma is a tumor-like lesion produced by a fungus (eumycetoma) or bacteria (actinomycetoma), typically encountered in arid areas rather than humid environments.3 These chronic, localized, nonpainful subcutaneous nodules develop on the foot and lower extremity after traumatic inoculation with the bacteria or fungus. Mycetomas persist for many years and classically present with a triad of tumefaction, draining sinus tracts, and “sulfur grains” that distinguish it from the dry, hyperkeratotic lesions of HLP. Diagnosis requires biopsy for histologic examination and both fungal and bacterial culture in order to choose the appropriate therapy.