To date, there is not a clear understanding of the pathogenesis of LA, although it is widely accepted that the amyloid material in LA is keratinocyte derived and is not associated with systemic disease. The amyloid material is restricted to the upper dermis in LA, and it is thought that chronic manipulation of the skin, either with the hand or with other implements, eventuates in keratinocyte death and amyloid deposition.
In LA, the lesions exist as hyperpigmented papules that coalesce to form thick plaques with a "sea floor-like" rippled appearance. The lesions are persistent and intensely pruritic. Most often the condition affects the pretibial surface, but the thighs, forearms, and back may be affected. Rare cases affecting the ears or the face exist in the literature. The condition is most common in Asian patients. The disorder is most prevalent in the 6th or 7th decade of life.
Interestingly, LA has been reported in association with a few syndromes, particularly multiple endocrine neoplasia type 2A (Sipple syndrome). The occurrence of LA in this syndrome is usually localized to the back in the intrascapular area, but it is otherwise histologically and biochemically identical to other forms of keratinocyte-derived LA unassociated with syndromic disease.
E85.4 – Organ-limited amyloidosis
282834007 – Lichen amyloidosis
- Notalgia paresthetica (NP) – This condition is identified by a persistent itching sensation of the upper back, usually over one or both scapulae or in the interscapular area. Most cases of NP, even in entirely normal individuals, are thought to have a neurogenic origin. There are usually no primary skin lesions, but changes secondary to persistent rubbing and scratching may lead to hyperpigmentation, excoriation, lichenification, and macular amyloidosis. NP scratching leads to cutaneous deposition of keratin-derived amyloid in some chronic cases. Itch caused by NP may be the underlying trigger for the rubbing and scratching associated with LA.
- Lichen simplex chronicus (LSC) – A form of neurodermatitis in which intensely pruritic plaques develop as a consequence of chronic manipulation; it is less likely to have the sea floor-like appearance and will not show superficial amyloid deposition on biopsy.
- Hypertrophic lichen planus (LP) – This form of LP very often affects the pretibial surface but may also affect the skin and mucosa elsewhere and does not show superficial amyloid deposition on biopsy.
- Papular mucinosis – This condition usually affects multiple areas beyond the pretibial surface and is associated often with an IgG paraproteinemia that is not present in LA.
- Pretibial myxedema – Associated with thyroid disease.