Primary cutaneous amyloidosis – pathology

The two primary cutaneous amyloidoses lichen and macular amyloidosis show similar histological features and so are described together.

Histology

The scanning power view can be relatively unremarkable. Figure 1. The key component of the histology is the deposition of pink amorphous material within the papillary dermis. This forms a number of scattered and confluent globular deposits. Figure 2, Figure 3, Figure 4. There is increased pigmentation of the basal layer and a scattered melanophages in the papillary dermis. Figure 4. The deposited material is identical in both macular and lichen amyloidosus, the difference is in the epidermal appearances. In lichen amyloidosus there is hyperkeratosis and epidermal hyperplasia which can range from mild to marked thickening. Figure 2. There may also be mild papillary dermal fibrosis. This is in keeping with the chronic excoriation underlying this condition, and the histological overlap with lichen simplex chronicus.

Primary cutaneous amyloidosis – pathology

Figure 1

Figure 2

Figure 3

Figure 4

Special stains

Congo-red highlights the deposits, and under polarization takes on a bright apple-green birefringence. Figure 5. There are significant limitations in the special stains for this condition. A positive reaction with this stain is not always readily seen, and false negatives not infrequently occur.

Primary cutaneous amyloidosis – congo red stain

Figure 5

Other less frequently used stains for cutaneous amyloid include crystal violet, pagoda red and methyl violet.

Cytokeratin (CK) staining can be used to identify the amyloid as epidermal in origin. Positive staining with immunostaining to kappa and lambda light chains is suggestive of AL amyloid deposition and should prompt consideration of systemic amyloidosis.

Differential diagnosis

This condition should be considered when faced with minimal pathological changes, aptly named an ‘invisible dermatosis’. The cutaneous amyloid deposits can easily be overlooked when not looked for specifically.

Draft 7 July 2010