While the cause of LA is incompletely understood, it is associated with, and probably caused by, friction and scratching with fingernails or implements such as towels or brushes.
Clinically, LA manifests as hyperpigmented papules that coalesce to form thick plaques with a "seafloor-like" rippled appearance. The most common location is the pretibial area, but the thighs, forearms, and back can also be involved. LA and macular amyloidosis (MA) are believed to exist on a spectrum and are mainly differentiated by the nature of the primary lesion (papules and plaques in LA and macules and patches in MA) and histopathologic findings. Some patients also display features of both LA and MA, which is termed "biphasic amyloidosis."
LA is intensely pruritic. LA has been reported in association with a few syndromes, particularly multiple endocrine neoplasia type 2A (Sipple syndrome). LA in this syndrome is usually localized to the back in the intrascapular area, and it is histologically and biochemically identical to other forms of keratinocyte-derived LA unassociated with syndromic disease.
E85.4 – Organ-limited amyloidosis
718105008 – Lichen amyloidosis
Differential Diagnosis & Pitfalls
- 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 otherwise healthy 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 MA. 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 seafloor-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 often associated with an immunoglobulin G (IgG) paraproteinemia that is not present in LA.
- Pretibial myxedema – Associated with thyroid disease.