When A Patient Presents With Itchy Red Plaques In The Lower Extremities

Tracey Vlahovic, DPM, FAPWCA

   It is also important to note the presence of Koebner’s phenomenon, which is the appearance of skin lesions in areas of skin trauma. This patient had the Koebner response after his cat scratched him. This manifested as linear versions of the polygonal violaceous lesions that followed the trauma of the scratch on his legs.

   In addition to its impact on the skin, this condition affects the mucous membranes 50 percent of the time and may also affect the genitalia, the scalp and the nails.3 Be aware that the oral lesions of lichen planus can occur without the skin manifestation and appear as a white reticulated pattern against a violaceous plaque on the buccal mucosa or tongue. The oral form of lichen planus can be associated with the presence of hepatitis C virus.4 Oral lichen planus can also be induced or made worse by exposure to metallic dental implements, and has a higher incidence in tobacco smokers.3 The rate of malignant transformation of oral lichen planus is reportedly low at 3 percent. However, there has been some debate as to determining the extent of disease in the oropharyngeal cavity and screening for signs of transformation.5

   It is been my clinical experience that the toenail disease is severe when present. Several nails are generally involved when it comes to lichen planus. Ten percent of the patients with lichen planus present with nail findings. The nails become thin, rough (trachyonychia), ridged (onychorrhexis), fissured and can develop a dorsal wing formation of the proximal nail fold (or pterygium formation) over the nail plate.6 If one does not address the matrix damage from the lichen planus, these nail findings become permanent scarred reminders of the skin disease that may never resolve.

What You Should Know About The Differential Diagnosis

Psoriasis and tinea corporis. When there is a characteristic red, scaly lesion that is bilateral and symmetrical, clinicians can easily confuse this with psoriasis and tinea corporis. Guttate psoriasis presents as small, salmon-pink colored droplets on the skin that are covered with a fine scale on the upper extremities and trunk. This skin eruption usually follows a Strep-based upper respiratory tract infection. Tinea corporis presents as an erythematous, scaly annular plaque, which eventually has central resolution of the lesion with an advancing border at the periphery.

   Lupus erythematosus. Due to lichen planus occurring on the generally sun exposed upper extremity, one must rule out lupus erythematosus. Patients who present with only scalp or oral lesions are particularly difficult to differentiate and a biopsy is necessary. If there is a malar rash (i.e. the characteristic butterfly facial rash) or atrophic scarring occurs following the initial skin rash on the sun exposed areas, physicians should strongly consider systemic lupus erythematosus and discoid lupus erythematosus.

   Pityriasis rosea and secondary syphilis. If the lesions began on the chest or back, and have begun to spread to the extremities, physicians should rule out pityriasis rosea. If the patient can remember a “herald patch” on the chest or back, that information is particularly helpful in diagnosing pityriasis rosea. Secondary syphilis is very similar in appearance to pityriasis rosea and is also a differential.

   Drug reaction. Lichen planus itself can be a response to an exogenous medication. Lichenoid drug eruptions or drug-induced lichen planus can be virtually indistinguishable both clinically and pathologically from idiopathic lichen planus. The most common drugs that may lead to these reactions are ACE inhibitors, thiazide diuretics and antimalarials.

   Onychomycosis. In the aforementioned patient case study, the nail disease was prevalent at the proximal nail plate and one could misdiagnose this as proximal subungual onychomycosis. It is important to look at all skin surfaces, ask pertinent questions and perform a nail culture/biopsy before placing a patient such as this on oral antifungals.

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