Lichenoid keratoses are common benign skin growths also known as lichen planus like keratoses. These are most often solitary, benign skin tumors and may be found anywhere on human skin. They are more common during adulthood. The keratosis may be misdiagnosed as a non-melanoma skin cancer, most commonly a superficial basal cell carcinoma.
Clinical Findings: Lichenoid keratoses are most frequently found on the upper trunk and upper extremities. The incidence is equal in males and females, and there is no race predilection. They are rare in childhood. They typically manifest as pruritic, red to slightly purple patches and thin plaques. Occasionally, a patient notices that the area arises in a preexisting seborrheic keratosis or solar lentigo. Most lichenoid keratoses are 1 cm or smaller in their largest diameter. Most patients present to their physician with a chief complaint of tenderness, itching, or bleeding secondary to scratching or rubbing of the lesion. The lesions may have a striking resemblance to the rash of lichen planus; the differentiating factor is that a lichenoid keratosis is solitary, whereas lichen planus includes a multitude of similar skin lesions. These skin growths have no malignant potential. It can be difficult to differentiate lichenoid keratoses from inflamed seborrheic keratoses, basal cell carcinomas, actinic keratoses, or squamous cell carcino- mas. Therefore, a biopsy of the lesion is prudent to discern a pathological diagnosis.
There are a few unusual clinical variants, including an atrophic form and a bullous type of lichenoid keratosis. The differential diagnosis of these two variants includes conditions such as lichen sclerosis for the former and autoimmune blistering diseases for the latter. The dermatoscope has become an indispensable tool and can be helpful in diagnosing lichenoid keratosis. Lichenoid keratoses have been shown to have a localized or diffuse granular-type pattern under dermatoscopic viewing. This finding should help differentiate these tumors from melanocytic tumors.
Histology: On histological examination, a lichenoid keratosis has a symmetric, well-circumscribed area of intense lichenoid inflammation along the basement membrane region. There is disruption of the basilar keratinocytes. This leads to the appearance of a number of necrotic keratinocytes, also called Civatte bodies. Civatte bodies are seen in almost all cases of lichenoid keratosis and also in lichen planus. There is pronounced sawtooth hypergranulosis and pronounced acanthosis. There is no atypia of the involved keratinocytes, thus ruling out an inflamed actinic keratosis. The underlying inflammatory infiltrate is made up almost entirely of lymphocytes. However, it is not uncommon to find a rare eosinophil or plasma cell anywhere throughout the infiltrate. The pathological differential diagnosis includes lichen planus. The clinical history is very important: Whereas a lichenoid keratosis is a solitary lesion, the same findings in a biopsy specimen taken from a widespread rash of purple, flat-topped papules would be more consistent with the diagnosis of lichen planus. This example illustrates the importance of including the clinical history on a pathology report.
Pathogenesis: The exact etiology of a lichenoid keratosis is unknown. It is believed to be caused by an inflammatory response to a lentigo or a thin seborrheic keratosis. The specific precipitating factor may be trauma. Chronic rubbing has been implicated in inducing lichenoid keratoses from lentigines. The role of human papillomavirus (HPV) in causing lichenoid keratoses has been studied, but no firm conclusions have been made.
Treatment: Most biopsies of a lichenoid keratosis result in complete resolution of the lesion. Even if the entire lesion was not removed with the biopsy specimen, no treatment is necessary. Use of a topical corticosteroid cream or ointment twice daily for 1 to 2 weeks after healing of the biopsy site is likely to lead to complete resolution of the lichenoid keratosis. Other treatment options include light cryotherapy or a light curettage after anesthesia. Benign lichenoid keratoses rarely if ever recur.