Lichenoid keratosis

What is lichenoid keratosis?

Lichenoid keratosis is a small, inflamed macule or thin pigmented plaque, usually solitary, with a lichenoid tissue reaction on histology.

Lichenoid keratosis is also known as benign lichenoid keratosis, solitary lichen planus, lichen planus-like keratosis and involuting lichenoid plaque. It is 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 can include minor trauma such as friction, drugs, dermatitis, and sun exposure. 

What are the clinical features of lichenoid keratosis?

• A solitary lesion is present in 90% of cases of lichenoid keratosis, with others presenting with multiple 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 asymptomatic. It may be itchy or have a mild stinging sensation.

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

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.

How is lichenoid keratosis diagnosed?

Lichenoid keratosis may be diagnosed clinically and confirmed on dermoscopy which reveals uniform clusters of grey dots [see Annular granular pattern dermoscopy]. Depending on the stage of the lesion, there may be signs of an original pre-existing lentigo or seborrhoeic keratosis which disappear with time. Later on the grey dots also disappear, as the lesion resolves.

A skin biopsy is required if clinical examination and dermoscopy cannot differentiate between lichenoid keratosis and other solitary erythematous lesions.

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

Grey dots

Annular granular pattern

Grey dots

What is the treatment of lichenoid keratosis?

If there is any doubt about the diagnosis, dermoscopy 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.

What is the outcome for lichenoid keratosis?

Lichenoid keratosis is harmless and resolves spontaneously.

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