The term amyloid refers to a heterogeneous group of extracellular proteins that structurally have a β-pleated sheet configuration and exhibit birefringence and dichroism under polarized light when stained with Congo red (see Chapter 5 and Fig 5-13). Amyloidosis is a group of diseases characterized by the deposition of specific amyloid proteins in various tissues and organs, often causing dysfunction of the affected tissues and organs. Common sources of amyloid proteins include
immunoglobulin light chain fragments (AL amyloid), in plasma cell dyscrasias
transthyretin, mutations in familial amyloid polyneuropathy types I and II
gelsolin, mutations in familial amyloidosis, Finnish type (also known as gelsolinamyloidosis or Meretoja syndrome)
Amyloid deposits within the eyelid skin are highly indicative of a systemic disease process, either primary or secondary, whereas deposits elsewhere in the ocular adnexa are more likely to represent a localized disease process. Other systemic diseases with eyelid manifestations are listed in Table 13-1. See BCSC Section 8, External Disease and Cornea, which discusses the classification of amyloidosis.
Figure 13-8 Xanthelasma. A, Patient with prominent xanthelasma. Note the yellow plaques on the medial upper and lower eyelids. B, Aggregates of foamy lipid-laden histiocytes are present in the dermis surrounding a venule (asterisk).
(Part A from External Disease and Cornea: A Multimedia Collection. American Academy of Ophthalmology; 1994:slide 10.)
Table 13-1 Eyelid Manifestations of Systemic Diseases
Figure 13-9 Cutaneous amyloidosis of the eyelid in multiple myeloma. Note the waxy elevation and the associated purpura of the lower lid, under the lesion.
(Courtesy of John B. Holds, MD.)
Figure 13-10 Epidermoid (epidermal inclusion) cyst in the dermis. The cyst lining resembles epidermis but does not contain skin appendages. The lumen contains keratin.
(Courtesy of Nasreen A. Syed, MD.)
Amyloid deposition in the skin is usually bilateral and symmetric and presents as multiple waxy yellow-white papules (Fig 13-9). The deposition of amyloid within blood vessel walls in the skin causes increased vascular fragility and often results in intradermal hemorrhages, accounting for the purpura seen clinically. On routine histologic sections, amyloid appears as an amorphous, eosinophilic extracellular deposit. Stains that are useful in demonstrating amyloid deposits include Congo red (see Chapter 10, Fig 10-12), crystal violet, and thioflavin T. Electron microscopy reveals that the deposits are composed of randomly oriented extracellular fibrils measuring 7–10 nm in diameter.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.