Cutaneous Amyloidosis
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Direct answer
Cutaneous amyloidosis is the deposition of amyloid fibrils within the skin, and it is either localised to the skin or a feature of systemic amyloid disease. Macular and lichen amyloidosis are primary forms that cause itch without internal organ involvement, while systemic disease shows skin signs such as purpura and waxy papules. Biopsy with Congo red staining, showing apple-green birefringence under polarised light, makes the diagnosis.
What you must remember
- Two broad groups: localised cutaneous forms with no systemic disease, and systemic amyloidosis with skin signs.
- Macular amyloidosis: pruritic, reticulated, grey-brown macules on the upper back, frequently reported in Asian patients.
- Lichen amyloidosis: intensely itchy, grouped papules on the shins and forearms, with amyloid deposited in the dermal papillae.
- Confirmatory stain: Congo red shows apple-green birefringence under polarised light; thioflavin T gives fluorescence as an alternative.
- Systemic clues: periorbital purpura, pinch purpura, macroglossia, waxy papules and bullae.
- Systemic types: AL amyloidosis linked to a plasma cell disorder, AA amyloidosis from chronic inflammation such as tuberculosis, and ATTR amyloidosis.
- Screen for AL disease: serum and urine immunofixation are the key tests when skin signs suggest systemic amyloid.
- Treatment of localised forms: topical steroids, topical calcineurin inhibitors and, for persistent macular disease, laser or phototherapy in selected patients.
Matching the form to the site and the risk
The same dye and the same protein can appear in very different settings, so the clinical question is whether the skin is the whole disease. The table lays out the common forms.
| Form | Typical site | Hallmark |
|---|---|---|
| Macular amyloidosis | Upper back | Pruritic, reticulated grey-brown macules |
| Lichen amyloidosis | Shins and forearms | Itchy, grouped, hyperkeratotic papules |
| Systemic AL | Skin, tongue, periorbital area | Purpura, macroglossia, plasma cell disorder |
| Systemic AA | Skin involvement uncommon | Chronic inflammatory or infective disease |
Localised forms need skin-directed care and no systemic screen. A patient with purpura and a tongue that looks enlarged needs the systemic workup first, since the cutaneous sign is only the visible part of the disease.
Biopsy settles the diagnosis at the bench, but the history decides the next step. An itchy, lichenified shin lesion in an otherwise well patient is managed in the clinic. Proteinuria, neuropathy or heart failure alongside skin signs sends the patient for systemic evaluation and haematology review.
Where the exam tries to catch you
Stems test whether you can separate a localised dermal deposit from a systemic diagnosis.
- Trap: assuming any cutaneous amyloid deposit means systemic amyloidosis. Correct: macular and lichen amyloidosis are localised and need no systemic screen, though a biopsy confirms the diagnosis.
- Trap: diagnosing amyloid from haematoxylin and eosin sections alone. Correct: Congo red staining with apple-green birefringence is the confirmatory test.
- Trap: missing AL amyloidosis in a patient with purpura and a plasma cell disorder. Correct: periorbital purpura and macroglossia call for serum and urine immunofixation.
Frequently asked questions
What distinguishes macular from lichen amyloidosis?
Macular amyloidosis produces reticulated, grey-brown, pruritic macules on the upper back, while lichen amyloidosis produces intensely itchy, grouped, hyperkeratotic papules on the shins and forearms. Both are primary cutaneous forms, and neither indicates systemic amyloid disease.
Which stain confirms amyloid in a skin biopsy?
Congo red staining confirms amyloid in a skin biopsy, and the diagnostic sign is apple-green birefringence under polarised light. Thioflavin T fluorescence is an alternative method used in many laboratories.
Which systemic amyloid type causes purpura and macroglossia?
Systemic AL amyloidosis, linked to a plasma cell disorder, typically causes periorbital purpura, macroglossia and waxy papules. Those skin findings should trigger serum and urine immunofixation, because the underlying clone needs treatment.
How is macular amyloidosis treated?
Macular amyloidosis is treated with topical steroids, topical calcineurin inhibitors and, in selected persistent cases, laser or phototherapy. It is usually a symptomatic and cosmetic problem, and the localised form does not need systemic therapy.