Macular amyloidosis (also known as friction amyloidosis) is a type of primary cutaneous amyloidosis.
Amyloidosis is a rare condition characterized by the extracellular deposition of amyloid in various organs.
Macular amyloidosis is a type of primary cutaneous amyloidosis, in which the amyloid deposits bind to antikeratin antibodies leading to the occurrence of small pigmented macules over the skin surface. Lichen and nodular amyloidosis are the other types of primary cutaneous amyloidosis. Macular and lichen amyloidosis may be present simultaneously leading to biphatic amyloidosis.
Macular amyloidosis is caused by the keratinocytes apoptosis due to trauma (for example, friction), genetic predisposition, infections, ultraviolet radiation, etc.
Primary cutaneous amyloidosis may be related to the bunch of other immune disorders, including:
- systemic sclerosis and CREST syndrome (a limited form of systemic sclerosis characterized by calcinosis, Raynaud’s phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia);
- rheumatoid arthritis;
- systemic lupus erythematosus;
- autoimmune cholangitis;
- ankylosing spondylitis;
- autoimmune thyroiditis;
Macular amyloidosis is also known to develop in association with Sipple syndrome, other features of which also include medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism.
See also: Amyloid heart disease
Macular amyloidosis is more common in the native Asians, South Americans and Middle Easterners. Females at the age between 20 and 50 years are more likely to develop macular amyloidosis than males.
In macular amyloidosis small brown or gray pruritic macules appear symmetrically on the upper back (especially interscapular area) and (less frequently) the extensor surface of the arms, in some cases chest and thighs may also be involved. A reticulated/rippled pattern is characteristic for these macules. Progressively macules interlock forming patches of darkened skin.
The rash may be itchy or asymptomatic.
The diagnosis is confirmed by performing a skin biopsy. Later the samples are painted with the Congo red stain, although it is not always enough sensitive to detect the small amounts of amyloid.
Treatment of macular amyloidosis includes both conservative and surgical measures.
Ultraviolet B (UV-B) light (narrow band and broadband) and PUVA (psoralen with UVA) phototherapy may be performed at least for 8 weeks as a symptomatic treatment.
If the previous treatment wasn’t effective dermabrasion, CO2 laser, and laser vaporisation are used as an alternative measure.
Lesion excision was suggested as an aggressive surgical treatment.
Medicines administered in the treatment of macular amyloidosis include the following:
- Topical corticosteroids (0,1% Betamethasone 17-valerate ointment);
- Topical anti-inflammatory agents such as Dimethyl sulfoxide (10-100%);
- Topical calcineurin inhibitors (0.1% Tacrolimus);
- Intralesional corticosteroids (Triamcinolone);
- Systemic retinoids (Acitretin);
- Systemic cyclophosphamide 50 mg per day;
- Sedating antihistamines (Chlorpheniramine, Diphenhydramine) are recommended to reduce the itching.