Lichen amyloidosis & macular amyloidosis
Primary localised cutaneous amyloidosis ยท friction amyloidosis
Lichen amyloidosis and macular amyloidosis are the two commonest forms of primary localised cutaneous amyloidosis (PLCA). They are characterised by deposition of keratinocyte-derived amyloid (mainly degenerated cytokeratins) in the papillary dermis. Both forms are markedly more common in Fitzpatrick IV-VI populations, particularly Southeast and East Asian, Middle Eastern and South American patients. The principal skin-oncology relevance is their role as a chronic mimic of mycosis fungoides (hyperpigmented MF), lichen simplex chronicus and post-inflammatory hyperpigmentation.
Pathogenesis
- Friction-induced apoptotic keratinocytes shed degenerated tonofilaments (cytokeratins 5/14) into the papillary dermis where they aggregate as amyloid.
- Familial cases linked to OSMR-ฮฒ / IL31RA mutations (autosomal dominant familial primary cutaneous amyloidosis).
- Strong predilection for Fitzpatrick IV-VI skin; female preponderance.
- Friction (towel rubbing, backscratchers, tight clothing) is a common trigger.
Clinical features
- Lichen amyloidosis: discrete, firm, hyperkeratotic, intensely pruritic papules; classically on shins (anterior) and extensor forearms; ripple / pebble pattern.
- Macular amyloidosis: rippled grey-brown hyperpigmented macules in symmetric reticulate / wavy pattern; upper back interscapular (classical), arms, extensor extremities.
- Biphasic amyloidosis: features of both.
- Pruritus often prominent โ drives friction perpetuation.
- Chronic, indolent, but socially distressing course.
Investigations
- Skin biopsy: papillary-dermal eosinophilic amyloid deposits; Congo-red apple-green birefringence; immunostain for cytokeratin (CK).
- No systemic involvement (PLCA distinguishes from systemic AL / AA amyloidosis).
- If multiple variants or unusual distribution, exclude systemic causes โ serum and urine electrophoresis, free light chains, echocardiogram.
- If familial: genetic counselling re OSMR / IL31RA.
Differentials
- Mycosis fungoides โ hyperpigmented / poikilodermatous variant โ biopsy + TCR gene rearrangement.
- Lichen simplex chronicus โ overlapping; single thick plaque.
- Notalgia paraesthetica / brachioradial pruritus โ neuropathic itch; reticulate macular amyloid commonly co-exists.
- Post-inflammatory hyperpigmentation.
- Frictional / hypertrophic lichen planus, prurigo nodularis.
- Acanthosis nigricans (interscapular variant).
Management
- Counsel about chronicity and the role of friction; stop towel-rubbing and back-scratching.
- Topical: potent corticosteroids ยฑ occlusion; intralesional triamcinolone for stubborn nodules; topical calcineurin inhibitors as steroid-sparing.
- Anti-pruritic: emollients, capsaicin, menthol, sedating antihistamines, gabapentin / pregabalin (for neuropathic component, notalgia paraesthetica).
- Phototherapy (NBUVB, PUVA) for diffuse disease.
- Acitretin, ciclosporin in refractory cases.
- Laser (CO2, fractional ablative) reported for cosmetically prominent lichen lesions.
- Dermabrasion, surgical excision for limited, persistent plaques.
References
- Tay CH, Dacosta JL. Lichen amyloidosis: clinical study of 40 cases. Br J Dermatol. 1970;83:23-30.
- Weidner T, Illing T, Elsner P. Primary localized cutaneous amyloidosis: a systematic treatment review. Am J Clin Dermatol. 2017;18:629-642.
- Mehrotra K et al. Primary cutaneous amyloidosis: review of treatment options. Indian Dermatol Online J. 2017;8:1-5.
- Tanaka A et al. Familial primary cutaneous amyloidosis: a search for genetic causation. J Invest Dermatol. 2009;129:2683-2692.
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