Lichenoid keratosis

What is lichenoid keratosis?

Lichenoid keratosis is usually a small, solitary, inflamed macule or thin pigmented plaque. Multiple eruptive lichenoid keratoses in sun-exposed sites are also described. Their colour varies from an initial reddish brown to a greyish purple/brown as the lesion resolves several weeks or months later.

Lichenoid keratosis is also known as benign lichenoid keratosis, solitary lichen planus, lichen planus-like keratosis and involuting lichenoid plaque. They are one of the causes of atypical solar lentigo.

Who gets lichenoid keratosis?

Lichenoid keratosis generally develops in fair-skinned patients aged 30–80 years. It is twice as common in females as than males. It is most commonly seen in Caucasians and rarely affects Asians, African Americans or Hispanics.

What causes lichenoid keratosis?

Lichenoid keratosis is an inflammatory reaction arising in a regressing existing solar lentigo or seborrhoeic keratosis. It is not known what causes the reaction, but triggers include minor trauma such as friction, drugs, dermatitis, and sun exposure.

How is lichenoid keratosis diagnosed?

Lichenoid keratosis is diagnosed by its clinical and dermoscopic appearance, which reveals uniform clusters of grey dots and, depending on the stage of the lesion, may show signs of an original pre-existing lentigo or seborrhoeic keratosis. In time, signs of the original lesion disappear. Later on the grey dots also disappear, as the lesion resolves to reveal normal skin.

Because clinical examination and dermatoscopy may not be able to differentiate between lichenoid keratosis and other solitary erythematous lesions that could be melanocytic, non-melanocytic benign, malignant or inflammatory, a punch or shave skin biopsy may be necessary.

Histopathology of resembles that of lichen planus or lichenoid drug eruption, with some slight differences. Remnants of the original solar lentigo or seborrhoeic keratosis may be evident.

What are the clinical features of lichenoid keratosis?

The clinical features of lichenoid keratosis vary depending on the inflammatory stage of the lesion.

Other features of lichenoid keratosis are:

• A solitary lesion is present in 90% of cases of lichenoid keratosis, with other patients presenting with few to many lesions.
• It is most commonly found on the upper trunk, followed by the distal upper extremities, and less commonly on the head and neck.
• Size ranges from a few millimetres to one centimetre or more in size.
• The skin surface may be smooth, scaly or warty.
• The lesion is often symptomless or it may be itchy or have a mild stinging sensation.

What is the management of lichenoid keratosis?

Lichenoid keratosis is harmless and resolves spontaneously. If there is any doubt about the diagnosis, dermatoscopic digital images can be taken and used in follow-up a few months later.

Lichenoid keratosis can be removed if desired by liquid nitrogen, electrosurgery or curettage.

Multiple eruptive lichenoid keratoses may be effectively treated with the oral retinoid, acitretin.

To date there have been no reports of lichenoid keratosis turning into malignant skin tumours.