Laboratory Studies
Normal serum protein electrophoresis and urine protein electrophoresis studies help to exclude multiple myeloma, which can also cause amyloid deposits made up of immunoglobulin light chains.
Positive antinuclear, anti-Ro, and anti-La antibody tests suggest Sjögren syndrome.
Laboratory studies, such as a complete blood cell count, serum chemistry profile, and liver function tests, often were part of a general workup in several case reports of patients with nodular localized cutaneous amyloidosis. Nodular localized cutaneous amyloidosis does not cause any abnormal findings in these studies.
Urinalysis or 24-hour urine testing can be performed to check for protein. Proteinuria is not a feature of localized cutaneous disease but can be seen in systemic amyloidosis.
Imaging Studies
In some patients, imaging studies have included chest radiography, electrocardiography, and abdominal ultrasonography.
Screening for amyloid within organs can be accomplished using scintigraphy with radioiodinated serum amyloid P component (ie, SAP scanning). This is a very sensitive test for detecting early systemic amyloidosis.
Procedures
Skin biopsy provides the definitive diagnosis. No special tissue preparation or handling is required before delivering the specimen to the laboratory. Special stains and immunohistochemistry are helpful.
An optimal biopsy specimen includes the epidermis, papillary dermis, and reticular dermis. The amyloid in nodular localized cutaneous amyloidosis is located in the reticular dermis and subcutaneous fat, and this finding clearly differentiates nodular localized cutaneous amyloidosis from other forms of amyloidosis. A shave biopsy or other superficial sample may not include enough reticular dermis to complete the diagnosis.
Consider bone marrow biopsy with gene rearrangement studies (if available) to exclude multiple myeloma.
Histologic Findings
Despite their biochemical heterogeneity, all "amyloid" deposits demonstrate a similar light microscopic appearance. They are eosinophilic and homogeneous when stained with hematoxylin and eosin and viewed with standard optics. When stained with Congo red and viewed with polarized light, deposits exhibit a characteristic apple-green birefringence. Pagoda red is even more specific for amyloid, and staining with thioflavin T is very sensitive.
In nodular amyloidosis, amyloid is not limited to the papillary dermis but is present in the entire dermis and may extend to subcutaneous fat. Amyloid deposition may be particularly prominent in walls of small blood vessels and surrounding individual lipocytes (see the images).
The bright pink homogeneous-appearing material seen is amyloid stained with Congo red. A distinguishing feature of amyloid in the skin is an affinity to take up Congo red stain.
This transmission electron micrograph of amyloid deposited in the tissue shows loosely interwoven straight filaments.
Plasma cells, which most likely produce the amyloid, occur within an adjacent and intermingled inflammatory infiltrate. They can be sparse or numerous (similar plasma cell infiltrate occurs in nodular pulmonary amyloidosis but usually is absent in cutaneous lesions of primary systemic amyloidosis). When eosinophilic amyloid material is exposed to potassium permanganate prior to staining with Congo red, the amyloid retains its congophilia, similar to systemic amyloidosis but in contradistinction to secondary amyloidosis. Kappa or lambda light chains (or both) may be present on immunohistochemical staining. [6]
When viewed with a transmission electron microscope, the apparently homogeneous deposits of amyloid are composed of loosely interwoven 6- to 10-nm–thick straight filaments. The amino acids of the filament proteins are arranged in a characteristic beta-pleated sheet tertiary structure. Amyloid deposits in the skin also contain small amounts of a plasma-derived, nonfibrillar, amyloid-P protein.
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The bright pink homogeneous-appearing material seen is amyloid stained with Congo red. A distinguishing feature of amyloid in the skin is an affinity to take up Congo red stain.
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Amyloid shows apple green when examined with polarized light.
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This transmission electron micrograph of amyloid deposited in the tissue shows loosely interwoven straight filaments.
