What is keratosis lichenoides chronica?
Keratosis lichenoides chronica presents with violaceous keratotic papules and nodules arranged in a linear or reticulate pattern on the trunk and limbs, in association with a seborrhoeic dermatitis-like eruption on the face [1,2].
Keratosis lichenoides chronica is also called Nekam disease, lichen verrucosus et reticularis, lichenoid trikeratosis, keratose lichenoide striae, porokeratosis striata lichenoides, and lichen ruber moniliformis.
Who gets keratosis lichenoides chronica?
Keratosis lichenoides chronica is rare, with only around 70 cases reported in the medical literature as of 2019 . It can occur in people of any race, age, or sex. The majority of cases have been described in adults aged 20–40 years; 24% of cases were children . The male to female ratio is 1.73 . Most reported cases have been Caucasians.
What causes keratosis lichenoides chronica?
The cause of keratosis lichenoides chronica is not well understood. It was initially thought to be a rare variant of lichen planus, but many now consider it to be a distinct condition .
Some familial cases of keratosis lichenoides chronica are due to a germline mutation in NLRP1, an inflammasome sensor gene that activates inflammatory cytokines. The aberrant activation of NLRP1 leads to the localised release of interleukin-1, secondary secretion of tumour necrosis factor-alpha and keratinocyte growth factor, resulting in epidermal hyperplasia and keratosis [3,4].
What are the clinical features of keratosis lichenoides chronica?
Keratosis lichenoides chronica is characterised by brownish-purple, thick scaly papules or small nodules on the trunk and extremities. The papules are generally arranged in a linear or reticular pattern and are symmetrically distributed. They are usually asymptomatic but can be itchy in 20% of cases. Keratosis lichenoides chronica has a chronic and often progressive course .
In 70% of cases, patients also present with facial lesions resembling seborrhoeic dermatitis or rosacea. The lesions are papules or plaques with variable hyperkeratotic scaling that tend to be localised to the convex areas of the face (eg, the forehead, cheeks, nose, and around the eyes and mouth). The nasolabial folds (smile lines) are almost always spared .
Other features associated with keratosis lichenoides chronica include :
- Palmoplantar keratoderma (seen in 28% of cases)
- Mucosal involvement with oral and genital ulceration, presenting as recurrent aphthous ulcers (in 28% of cases) — these are more common in adults than in children
- Nail involvement with dystrophy, discolouration, longitudinal ridging, hyperkeratosis of the nail bed, or paronychia (27%)
- Ocular involvement with blepharitis, conjunctivitis, uveitis, or iridocyclitis (20%)
- Non-scarring alopecia of the eyebrows and scalp (7%) — this more commonly affects children.
Keratosis lichenoides chronica has also been reported in conjunction with renal disease, diabetes, hypothyroidism, lymphoma, hepatitis, and tuberculosis .
What are the complications of keratosis lichenoides chronica?
Complications of keratosis lichenoides chronica include visual impairment from ocular manifestations and secondary bacterial infection .
How is keratosis lichenoides chronica diagnosed?
The criteria for diagnosing keratosis lichenoides chronica have not been well established .
The main differential diagnosis is lichen planus; the features distinguishing keratosis lichenoides chronica from lichen planus are the absence of pruritus, a lack of response to a topical or systemic corticosteroid, and the presence of focal parakeratosis in histological samples.
A skin biopsy is recommended for the histological diagnosis of keratosis lichenoides chronica. Histology typically shows:
- Variable epidermal changes, which can include hyperkeratosis, follicular parakeratosis, and alternating areas of acanthosis and atrophy
- A lichenoid reaction pattern with keratinocyte necrosis and vacuolar degeneration in the basal layer
- A mixed inflammatory infiltrate of lymphocytes, plasma cells, histiocytes, and occasionally eosinophils.
Direct immunofluorescence is typically negative .
What is the differential diagnosis for keratosis lichenoides chronica?
Several other conditions can present with pigmented papules and lichenoid histology. These include:
- Hypertrophic lichen planus — characterised by pruritus and follicular accentuation of hyperkeratosis, which do not occur in keratosis lichenoides chronica 
- Lichen planopilaris — associated with scarring alopecia, a feature never reported in keratosis lichenoides chronica 
- Discoid lupus erythematosus — also associated with scarring alopecia
- Cutaneous lupus erythematosus — which is typically photosensitive, whereas keratosis lichenoides chronica generally improves with sun exposure .
What is the treatment for keratosis lichenoides chronica?
Keratosis lichenoides chronica is very resistant to available therapies. A recent review found that most patients experience improvement with sun exposure and that oral retinoids (eg, acitretin) and phototherapy, specifically photochemotherapy (PUVA), either alone or in combination are the most effective treatments .
Topical agents such as steroid creams are usually ineffective. Systemic agents that have been reported to be useful in some patients include:
- Systemic corticosteroids
- Sulfones (eg, dapsone)
- Antimalarial agents
What is the outcome for keratosis lichenoides chronica?
Keratosis lichenoides chronica is very difficult to treat, and in most cases, remission is never achieved. Complete resolution has never been reported .