Cutaneous manifestations of amyloidosis

INTRODUCTION — Amyloidosis is the abnormal deposition of amyloid (insoluble fibrils comprised of beta-pleated sheets of protein) in extracellular tissues. Amyloid appears microscopically as globules of eosinophilic, homogeneous, hyaline material.

The deposition of amyloid in the skin can occur as a skin-limited disorder (primary localized cutaneous amyloidosis and secondary localized cutaneous amyloidosis). Cutaneous amyloidosis may also occur as a manifestation of systemic amyloidosis, most often in immunoglobulin light chain (AL) amyloidosis.

The clinical manifestations, diagnosis, and management of cutaneous amyloidosis, with a focus on primary localized cutaneous amyloidosis, will be reviewed here. Systemic amyloidosis is reviewed in detail separately.

●(See "Overview of amyloidosis".)

●(See "Monoclonal immunoglobulin deposition disease".)

●(See "Clinical presentation, laboratory manifestations, and diagnosis of immunoglobulin light chain (AL) amyloidosis".)

●(See "Treatment and prognosis of immunoglobulin light chain (AL) amyloidosis".)

●(See "Causes and diagnosis of AA amyloidosis and relation to rheumatic diseases".)

●(See "Treatment of AA (secondary) amyloidosis".)

●(See "Genetic factors in the amyloid diseases".)

OVERVIEW — The pathogenesis of amyloidosis involves the extracellular deposition of insoluble amyloid fibrils comprised of soluble precursor proteins that undergo conformational changes to form a predominantly antiparallel beta-sheet configuration [1]. A wide variety of normal and abnormal precursor proteins can lead to amyloid formation, resulting in multiple amyloid types (table 1). The principles of fibril formation are reviewed separately. (See "Overview of amyloidosis", section on 'Pathogenesis'.)

Of the many types of amyloid described (table 1), only some are associated with cutaneous manifestations (eg, amyloid K [AK], amyloid light chain [AL], amyloid A [AA], A beta-2 microglobulin, and amyloid transthyretin [ATTR]). The major cutaneous manifestations of amyloidosis (and their associated subtypes of amyloid) can be subdivided as follows [2]:

●Localized cutaneous amyloidosis:

•Primary localized cutaneous amyloidosis:

-Macular amyloidosis (AK)

-Lichen amyloidosis (AK)

-Nodular amyloidosis (AL)

-Pharmaceutical (injection site) amyloidosis (AIns)

-Familial primary localized cutaneous amyloidosis (AK)

•Secondary localized cutaneous amyloidosis (predominantly AK)

●Systemic amyloidosis with cutaneous involvement:

•Immunoglobulin light chain (AL) amyloidosis (previously referred to as primary amyloidosis)

•Secondary (AA) amyloidosis

•Dialysis-related amyloidosis (A beta-2 microglobulin amyloid)

•Heredofamilial amyloidoses (eg, ATTR amyloid [most common])

While the various types of amyloid appear similar on light microscopic examination and exhibit similar properties on special stains (metachromatic staining with crystal violet and methyl violet, green birefringence with Congo red viewed under polarized light, and yellow-green fluorescence with thioflavin T), they represent vastly different diseases with pronounced differences in prognosis and treatment [1,3,4]. As examples, macular and lichen amyloidosis are skin-limited diseases with no potential for visceral involvement. Nodular amyloidosis is skin limited but represents a localized plasma cell dyscrasia and carries a small risk of progression to systemic disease. AL amyloidosis is a plasma cell dyscrasia with significant morbidity and mortality.

LOCALIZED CUTANEOUS AMYLOIDOSIS — The major types of localized cutaneous amyloidosis include macular amyloidosis, lichen amyloidosis, nodular amyloidosis, familial primary localized cutaneous amyloidosis (PLCA), and secondary localized cutaneous amyloidosis. Rare variants of cutaneous amyloidosis include poikiloderma-like cutaneous amyloidosis and amyloidosis cutis dyschromica. (See 'Rare variants' below.)

Macular and lichen amyloidosis — Macular amyloidosis and lichen amyloidosis are uncommon skin-limited conditions that may represent a clinical spectrum of a single disease process. These clinical presentations may be most likely to occur in South American, Asian, or Middle Eastern individuals [5-7] and usually arise in adulthood [5].

Most cases are sporadic. However, macular amyloidosis and lichen amyloidosis also represent the most common manifestations of familial PLCA [8]. In a series of 794 Chinese patients with primary cutaneous amyloidosis (primarily lichenoid, biphasic, and macular amyloidosis), 7 percent had a positive family history of cutaneous amyloidosis [5]. (See 'Familial primary localized cutaneous amyloidosis' below.)

Pathogenesis — The amyloid deposits in macular amyloidosis and lichen amyloidosis are derived from keratin intermediate filament proteins. Degeneration of basal keratinocytes in the overlying epidermis likely plays a role. In one theory, cytokeratin released from apoptotic basal keratinocytes is covered with autoantibodies, phagocytosed by macrophages, and enzymatically degraded to form amyloid K [4]. In addition, sweat gland or sweat duct dysfunction leading to leakage of sweat into the dermoepidermal junction, an inflammatory response, epidermal damage, and amyloid deposition has been proposed as a pathogenic mechanism for lichen amyloidosis [9].  

A cycle of chronic pruritus and scratching may contribute to amyloid production and deposition. Pruritic conditions such as chronic kidney disease and biliary cirrhosis are potential triggers.

Clinical features — Macular amyloidosis classically appears as hyperpigmented, thin plaques, often containing "rippled" linear gray-tan streaks (picture 1A-B). Typical sites of involvement are the upper back (scapula region) and extensor surfaces of extremities. Macular amyloidosis is usually, but not always, pruritic.

Lichen amyloidosis is pruritic and appears as discrete, skin-colored to hyperpigmented, scaly, domed, 2 to 4 mm papules that coalesce to form persistent plaques with a rippled appearance (picture 2A-E). The plaques are most commonly found on the extensor surfaces, such as the shins. Lichen amyloidosis usually begins unilaterally but may progress to symmetric involvement. Bullae occur in rare cases [10].

The typical anatomic locations for lichen amyloidosis may correlate with areas that can be easily scratched or rubbed. Patients with pretibial lichen amyloidosis often acknowledge chronic rubbing of the heel of the contralateral leg along the shin.

Some patients exhibit overlapping features of macular and lichen amyloidosis. This phenomenon has been termed biphasic amyloidosis [10].

Histopathology — The various subtypes of disease are distinguished in skin biopsies by the pattern and location of amyloid deposition and immunohistochemical properties. In both macular amyloidosis and lichen amyloidosis, small globules of pink material (amyloid) are present in the superficial dermis, mostly in dermal papillae between epidermal rete ridges [3]. The overlying epidermis may demonstrate degeneration of basal keratinocytes with cytoplasmic vacuolization. Pigment incontinence is also common, with admixed melanophages, which may have a dendritic morphology.

In addition, lichen amyloidosis demonstrates hyperkeratosis and epidermal acanthosis that may resemble lichen simplex chronicus. The epidermis of macular amyloidosis typically appears normal.

Amyloid deposition is not present around blood vessel walls or deeper in the dermis in either disorder, and plasma cells are generally not increased in affected skin [4]. The keratinocyte-derived amyloid stains with Congo red, crystal violet, and thioflavin T stains and is positive on keratin-specific immunohistochemical stains such as cytokeratin 5 [11].

Diagnosis — A diagnosis of macular amyloidosis or lichen amyloidosis is suspected based upon the recognition of consistent clinical findings (hyperpigmented, rippled, thin plaques for macular amyloidosis and skin-colored or hyperpigmented, dome-shaped papules coalescing into plaques for lichen amyloidosis), particularly when found in a characteristic location (eg, upper back for macular amyloidosis, shins for lichen amyloidosis). There is often a history of pruritus and scratching in the affected area.

The diagnosis is confirmed by the detection of amyloid with a skin biopsy. A punch biopsy is the preferred type of biopsy. (See "Skin biopsy techniques", section on 'Punch biopsy' and 'Histopathology' above.)

Differential diagnosis — A careful skin examination will often identify features that suggest alternative diagnoses. A skin biopsy demonstrating amyloid deposits distinguishes amyloidosis from other disorders.

The differential diagnosis of macular amyloidosis often includes:

●Notalgia paresthetica – Notalgia paresthetica is considered a form of neuropathic itch that occurs on the back, medial to the scapular border (picture 3). The pruritus is usually unilateral and may be in a dermatomal distribution. Hyperpigmentation often occurs secondary to scratching or rubbing the skin. Amyloid deposits are not a primary histologic feature of notalgia paresthetica; however, chronic scratching of the affected area may contribute to the development of associated macular amyloidosis. (See "Pruritus: Etiology and patient evaluation", section on 'Notalgia paresthetica'.)

●Tinea versicolor – Tinea versicolor is a common cutaneous fungal infection that manifests as hyperpigmented or hypopigmented scaly patches on the skin, particularly the trunk (picture 4). A potassium hydroxide preparation will show fungal hyphae and spores. (See "Tinea versicolor (pityriasis versicolor)".)

●Confluent and reticulated papillomatosis – Confluent and reticulated papillomatosis is an uncommon disorder that usually occurs in young adults and manifests as reticulated hyperpigmented keratotic papules on the trunk (picture 5). A skin biopsy can differentiate between confluent and reticular papillomatosis and macular amyloidosis. (See "Confluent and reticulated papillomatosis".)

Other disorders that may be mistaken for macular amyloidosis include drug-induced pigmentation and other cutaneous dyschromias, such as erythema dyschromicum perstans (ashy dermatosis) and actinic lichen planus (picture 6A-B). These conditions typically lack the rippled appearance often present in macular amyloidosis.

The differential diagnosis of lichen amyloidosis primarily consists of disorders that may manifest with plaques on the extensor surfaces of the extremities. Examples of disorders in the differential diagnosis include:

●Lichen simplex chronicus – Lichen simplex chronicus is a reactive thickening of the skin related to chronic pruritus and scratching (picture 7). Often, there is an underlying pruritic dermatosis, such as atopic dermatitis. Clinically, lichen amyloidosis has a more rippled appearance than lichen simplex chronicus.

●Prurigo nodularis – Prurigo nodularis is characterized by pruritic, scaly nodules and commonly occurs on the extensor surfaces of the extremities (picture 8). As with lichen amyloidosis, the itch-scratch cycle plays an important role in development. Prurigo nodularis is commonly associated with other pruritic skin disorders, such as atopic dermatitis. (See "Prurigo nodularis".)

●Hypertrophic lichen planus – Hypertrophic lichen planus classically presents as hypertrophic, violaceous, thick plaques with overlying scale (picture 9). The shins are common sites for this disorder. A distinctive histologic finding of lichen planus is a band-like lymphocytic infiltrate in the superficial dermis. (See "Lichen planus", section on 'Cutaneous variants'.)

●Localized lichen myxedematosus – Localized lichen myxedematosus is a rare disorder that presents with multiple waxy papules in a linear arrangement or coalescing into plaques. A skin biopsy will demonstrate abundant mucin. (See "Localized lichen myxedematosus".)

●Pretibial myxedema – Pretibial myxedema is an infiltrative mucinosis of the skin that usually occurs in association with Graves’ disease. Pretibial myxedema commonly presents as thickened nodules or plaques on the shins (picture 10). An association with thyroid disease and a skin biopsy demonstrating abundant mucin define this entity. (See "Pretibial myxedema (thyroid dermopathy) in autoimmune thyroid disease".)

●Elephantiasis nostras verrucosa – Chronic lymphedema may lead to sclerotic thickening of the skin with a "mossy" and papillomatous appearance. The chronic lymphedema should alert the clinician to this entity. (See "Clinical features and diagnosis of peripheral lymphedema".)

Treatment — Macular amyloidosis and lichen amyloidosis are skin-limited diseases with no potential for visceral involvement; therefore, the goals of treatment are to improve associated symptoms and cosmesis. Although a variety of treatments have been employed, efficacy data are limited and high-quality randomized trials are lacking, leaving the best approach to treatment unclear. No treatment is consistently effective or curative:

●First-line therapy – Given the benign nature of these disorders, a conservative initial approach to treatment is preferred. Clinical experience suggests that interventions to break the itch-scratch cycle can be helpful. Patients should be encouraged to avoid scratching or rubbing affected areas; occlusive dressings are helpful when needed. In addition, a potent (group 1 or 2) topical corticosteroid can be applied once or twice daily (table 2). For thick plaques of lichen amyloidosis, the topical corticosteroid can be applied under occlusion to augment drug penetration.

If there is no improvement after one month, topical corticosteroid therapy should be discontinued. Cutaneous atrophy is a potential side effect of topical corticosteroid use.

Clinical experience suggests that intralesional corticosteroid therapy (eg, triamcinolone acetonide 10 mg/mL) can be a useful alternative to topical corticosteroid therapy for patients with small, localized areas of lichen amyloidosis [4]. As with topical corticosteroids, there is a risk of cutaneous atrophy. A case report suggests that topical tacrolimus may be a topical alternative; treatment with tacrolimus 0.1% ointment twice daily for two months was associated with improved pruritus and reduced thickness of plaques in a patient with lichen amyloidosis [12]. An advantage of topical tacrolimus is the absence of risk for cutaneous atrophy.

Topical keratolytic agents, such as salicylic acid or urea, are helpful for removing associated scale.

●Other therapies – Limited data primarily from case reports, case series, and small, uncontrolled studies suggest that skin moisturizers applied under occlusion [9], physical interventions (eg, phototherapy [13-18], laser therapy [19], and dermabrasion [20,21]), and systemic medications (eg, oral retinoids [22], cyclosporine [15,23,24], cyclophosphamide [25], and thalidomide [26]) may improve macular amyloidosis or lichen amyloidosis. Use of these therapies is usually reserved for patients who fail to respond to first-line interventions. Associated risks should be carefully considered prior to treatment.

Few studies have directly compared interventions, leaving uncertainty about relative efficacy. An open left-right comparison study that compared the efficacy of moderate to potent topical corticosteroids with the efficacy of ultraviolet B (UVB) or psoralen plus ultraviolet A (PUVA) phototherapy in 20 patients with a clinical diagnosis of lichen amyloidosis found a trend towards greater reductions in patient-reported itch and skin roughness with phototherapy, but the difference was not statistically significant [13]. In a single-blind randomized trial that compared treatment with superficial and deep modes of a fractional carbon dioxide laser in 16 patients with macular amyloidosis and nine patients with lichen amyloidosis, both modes were associated with reduced pigmentation, thickness, itching, and amyloid deposits in treated areas [27]. The superficial mode induced less pain.

Nodular amyloidosis — Nodular amyloidosis (also known as tumefactive amyloidosis) is rare, occurring less often than macular amyloidosis and lichen amyloidosis [28]. Nodular amyloidosis usually occurs in adults [29]. There does not appear to be a sex predilection [29].

Nodular amyloidosis is skin limited but represents a localized plasma cell dyscrasia. There is a small risk of progression to systemic amyloidosis (between 1 and 7 percent in different series) [30-32]. An association with Sjögren's disease has been proposed [29,31].

Pathogenesis — The amyloid in nodular amyloidosis is immunoglobulin derived and contains either lambda (most common) or kappa light chains [33]. The immunoglobulins appear to be derived from a clonal population of skin-homing plasma cells [10].

Clinical features — Nodular amyloidosis presents as asymptomatic, solitary or multiple, waxy nodules or plaques on the head, trunk, or extremities (picture 11A-B). There is a predilection for acral sites. The color of nodules is usually yellow to brown, and the diameter of nodules typically ranges from 0.5 to 7 cm [29]. The overlying skin may appear atrophic, and the nodules may have associated purpura.

Histopathology — The classic histologic findings of nodular amyloidosis are diffuse infiltrates of amyloid in the dermis, subcutis, and blood vessel walls [32]. Plasma cell infiltrates are found in close proximity to the amyloid deposits [3]. Kappa and lambda light chain immunostains or in situ hybridization studies may demonstrate plasma cell clonality. Antikeratin antibody stains are negative [3].

Diagnosis and evaluation — The clinical features of nodular amyloidosis overlap with multiple other disorders. A skin biopsy demonstrating amyloid is required to confirm the diagnosis. A deep shave biopsy or a punch biopsy is usually sufficient. (See "Skin biopsy techniques".)

An evaluation for systemic amyloidosis is recommended at the time of diagnosis because of the risk for progression of nodular amyloidosis to systemic disease. The initial workup should include a complete review of systems and full physical examination. Studies should include:

●Complete blood count

●Comprehensive metabolic panel

●Serum protein electrophoresis and immunofixation

●Urine protein electrophoresis and immunofixation

●Electrocardiogram

The clinical features and diagnosis of immunoglobulin light chain amyloidosis are reviewed in detail separately. (See "Clinical presentation, laboratory manifestations, and diagnosis of immunoglobulin light chain (AL) amyloidosis".)

The potential for progression of nodular amyloidosis to systemic amyloidosis warrants ongoing follow-up. Periodic assessments with a review of systems, complete physical examination, and laboratory tests are indicated after diagnosis. We reevaluate patients at least once yearly.

Differential diagnosis — The differential diagnosis of nodular amyloidosis includes other disorders that may present with smooth nodules or nonscaly plaques on the skin. Examples of disorders in the differential diagnosis include cutaneous lymphoma, leukemia cutis, pseudolymphoma, sarcoidosis, and granuloma annulare. A biopsy will distinguish nodular amyloidosis from other conditions.

Treatment — Treatment of nodular amyloidosis is not mandatory but can be employed for the purpose of improving the appearance of lesions. Treatment involves physical removal or destruction of the nodules. Recurrences are common after treatment.

Surgical excision is a common removal technique. Shave excisions have yielded favorable results for facial nodular amyloidosis in case reports [34]. Other treatments described as beneficial in case reports include electrodesiccation [35], dermabrasion [32,36], and laser treatment with carbon dioxide or pulsed dye lasers [19]. Some of the risks of these procedures include pain, dyspigmentation, infection, and scarring.

Pharmaceutical (injection site) amyloidosis — Injections of certain medications may result in subcutaneous amyloid deposits, believed to represent complexes of amyloid and the injected material, which resemble nodular amyloidosis clinically and microscopically. This phenomenon has been most commonly reported in association with insulin (both porcine and recombinant human forms) and has been alternately referred to as pharmaceutical amyloidosis, amyloidoma, or "insulin ball" [37-40]. Repeated subcutaneous injections of insulin into the same soft tissue site is reported as a risk factor for development. Enfuvirtide, an antiretroviral medication known to commonly cause injection site reactions, has also been implicated in this phenomenon [40-42].

Clinical features for both medications include subcutaneous nodules or firm, nodular plaques with overlying hyperpigmentation and/or ecchymosis, which appear in areas of soft tissue such as the abdominal pannus and thighs. Microscopic features include amorphous deposits of hyaline pink, homogenous material within the deep dermis and subcutaneous fat lobules that exhibit typical apple green birefringence on polariscopic examination with Congo red staining [37,42]. These deposits do not stain positively for AA amyloid or kappa or lambda light chains but may exhibit apolipoprotein expression [37,42].

Local treatment is preferred; surgical excision is reported as curative [40]. Patients should take care to avoid prior sites of involvement when performing future injections.

Familial primary localized cutaneous amyloidosis — The clinical manifestations of familial primary localized amyloidosis (PLCA), a rare hereditary disorder, typically resemble sporadic macular amyloidosis and sporadic lichen amyloidosis [8]. Familial PLCA usually presents between the ages of 5 and 18 years. An autosomal dominant pattern of inheritance has been detected in families in Japan, China, Taiwan, and Brazil. Mutations in the oncostatin M receptor beta (OSMRB) and interleukin-31 receptor A (IL31RA) genes have been found in affected families [43].

Familial cases of macular amyloidosis and lichen amyloidosis may also occur in association with multiple endocrine neoplasia type 2A with mutations in the RET proto-oncogene [44]. The approach to treatment is similar to sporadic disease. (See "Clinical manifestations and diagnosis of multiple endocrine neoplasia type 2" and 'Treatment' above.)

Secondary localized cutaneous amyloidosis — Secondary localized cutaneous amyloidosis is the incidental finding of small amounts of amyloid in diseased skin. Secondary localized cutaneous amyloidosis is usually found in cutaneous tumors but has also occurred in other cutaneous diseases [45,46]. The amyloid in secondary localized cutaneous amyloidosis is thought to be derived from keratinocytes [45]. Immunostaining for cytokeratin is usually positive [6].

Rare variants — Rare clinical variants of primary cutaneous amyloidosis include poikiloderma-like cutaneous amyloidosis and amyloidosis cutis dyschromica:

●Poikiloderma-like cutaneous amyloidosis – Poikiloderma-like cutaneous amyloidosis is characterized by poikiloderma-like skin changes, lichenoid papules, and blisters. Most reported cases have occurred on the extremities; however, involvement of the trunk is documented [47]. Skin biopsies show amyloid deposits in the papillary dermis. A syndromic form of poikiloderma-like cutaneous amyloidosis is associated with photosensitivity, short stature, and occasional palmoplantar keratosis [47].

●Amyloidosis cutis dyschromica – Amyloidosis cutis dyschromica is a rare sporadic or familial form of cutaneous amyloidosis that manifests as widespread, symmetric, macular or reticulate hyperpigmentation mixed with guttate hypopigmented macules (picture 12) [48]. The disorder may be asymptomatic or pruritic. Skin biopsies demonstrate amyloid deposits in the papillary dermis. Improvement with oral acitretin therapy has been reported [48].

SYSTEMIC AMYLOIDOSES WITH CUTANEOUS INVOLVEMENT — Cutaneous findings may occur in immunoglobulin light chain (AL) amyloidosis, secondary systemic (AA) amyloidosis, dialysis-associated systemic amyloidosis, and some hereditary amyloidoses:

●AL amyloidosis – Approximately 40 percent of patients with AL amyloidosis have cutaneous findings (picture 13A-B). Fundamental skin lesions include domed, shiny or waxy-appearing papules, which appear translucent and may resemble vesicles or small bullae. These lesions tend to aggregate around mucocutaneous junctions such as the orbits, the nares, cutaneous lips, and genital skin. Patients may also develop nodules resembling nodular amyloidosis. (See "Clinical presentation, laboratory manifestations, and diagnosis of immunoglobulin light chain (AL) amyloidosis".)

Purpura is another common skin finding. Purpura result from blood vessel fragility due to vascular amyloid deposition and preferentially affect sites of thin skin, such as the eyelids. Purpura may be triggered by light trauma or increased hydrostatic pressure, such as the Valsalva maneuver. Patients may also exhibit nonspecific skin findings seen in depositional disorders (eg, alopecia, nail dystrophies, macroglossia) (picture 14A-B) [2].

Histopathologic findings include amyloid deposits in the dermis that may extend into the subcutis, where amyloid deposits may surround individual fat cells [3]. Purpuric areas may exhibit amyloid deposits in the walls of dermal blood vessels. More than 50 percent of biopsies of normal skin demonstrate amyloid deposits in the dermis [3,49].

●AA amyloidosis – Cutaneous involvement in AA amyloidosis is rare [50]. Petechiae, purpura, and alopecia have been reported [49]. In addition, amyloid deposits may be detected in clinically normal skin. In one series, 5 of 12 patients with this form of systemic amyloidosis had amyloid deposits in normal-appearing skin [49]. (See "Causes and diagnosis of AA amyloidosis and relation to rheumatic diseases".)

●Dialysis-associated amyloidosis – Cutaneous involvement in dialysis-associated amyloidosis is rare. Potential manifestations include hyperpigmentation, lichenoid eruptions, or nodules that demonstrate amyloid deposits on histopathologic examination [51]. (See "Dialysis-related amyloidosis".)

●Heredofamilial amyloidosis – The most common hereditary variant of systemic amyloidosis is hereditary transthyretin amyloidosis, which is related to the deposition of amyloid transthyretin (ATTR). Cutaneous manifestations can include atrophic scars, persistent ulcers, or petechiae [4]. Cutaneous findings may also occur in other hereditary systemic amyloidoses, such as hereditary apolipoprotein A1 amyloidosis (maculopapular eruptions and petechiae), tumor necrosis factor-receptor 1 associated periodic fever syndrome (migrating cutaneous erythemas), hereditary gelsolin amyloidosis (cutis laxa, pruritus, petechiae, ecchymoses, hypotrichosis, and alopecia), and Muckle-Wells syndrome (pruritus and cold urticaria-like eruptions) [4]. (See "Genetic factors in the amyloid diseases", section on 'AA amyloid and the inherited systemic autoinflammatory diseases'.)

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●Basics topics (see "Patient education: AL amyloidosis (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Overview – The cutaneous manifestations of amyloidosis include skin-limited disorders (primary localized cutaneous amyloidosis and secondary localized cutaneous amyloidosis) as well as cutaneous manifestations of systemic amyloidoses. (See 'Overview' above.)

●Localized cutaneous amyloidosis – The primary localized cutaneous amyloidoses include macular amyloidosis, lichen amyloidosis, and nodular amyloidosis. Macular amyloidosis and lichen amyloidosis are the most common types of primary localized cutaneous amyloidosis. Secondary localized cutaneous amyloidosis is the presence of incidental amyloid deposits in cutaneous tumors or other cutaneous diseases. (See 'Localized cutaneous amyloidosis' above.)

•Macular amyloidosis and lichen amyloidosis – Macular amyloidosis and lichen amyloidosis may represent a clinical spectrum of a single disease process. Amyloid in these disorders is derived from keratin intermediate filament proteins and likely results from the degeneration of basal keratinocytes. A cycle of chronic pruritus and scratching may contribute to the development of macular amyloidosis and lichen amyloidosis. (See 'Macular and lichen amyloidosis' above.)

Macular amyloidosis classically presents as hyperpigmented, thin plaques with rippled linear streaks (picture 1A-B). The upper back and extensor surfaces of extremities are common sites. Lichen amyloidosis characteristically presents with skin-colored to hyperpigmented scaly, dome-shaped papules that coalesce to form plaques with a rippled appearance (picture 2A-E). Lichen amyloidosis usually occurs on the extensor surfaces of extremities. (See 'Macular and lichen amyloidosis' above.)

•Nodular amyloidosis – Nodular amyloidosis typically presents with single or multiple, asymptomatic, yellow-brown, waxy nodules or plaques on the trunk or extremities. The amyloid in nodular amyloidosis is composed of immunoglobulin light chains. In contrast to macular amyloidosis and lichen amyloidosis, nodular amyloidosis is associated with risk of progression to systemic amyloidosis. Patients with nodular amyloidosis should be evaluated for systemic disease. (See 'Nodular amyloidosis' above.)

•Diagnosis of localized cutaneous amyloidosis – A skin biopsy is necessary to confirm a diagnosis of macular amyloidosis, lichen amyloidosis, or nodular amyloidosis. (See 'Diagnosis' above and 'Diagnosis and evaluation' above.)

•Treatment of localized cutaneous amyloidosis – Treatment of primary localized cutaneous amyloidosis is not mandatory. Treatment is performed to improve symptoms and/or cosmesis. (See 'Treatment' above and 'Treatment' above.)

-Macular amyloidosis and lichen amyloidosis – No treatment is consistently effective for macular amyloidosis and lichen amyloidosis. We suggest interventions to minimize pruritus and scratching as initial treatment (Grade 2C). Our initial treatment approach consists of local corticosteroid therapy to reduce pruritus. Other interventions that may be useful for patients who fail to improve with these conservative measures include phototherapy, laser, dermabrasion, and systemic medications. (See 'Treatment' above.)

-Nodular amyloidosis – Nodular amyloidosis can be treated with surgical excision or other destructive procedures. Recurrence is common. (See 'Treatment' above.)

●Systemic amyloidosis – Systemic amyloidoses with cutaneous manifestations include immunoglobulin (AL) light chain amyloidosis, secondary systemic (AA) amyloidosis (rare skin involvement), dialysis-related amyloidosis (rare skin involvement), and various hereditary variants of systemic amyloidosis. (See 'Systemic amyloidoses with cutaneous involvement' above.)