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Free keywords:
familial transthyretin amyloidosis; lymphatic vessel; skin biopsy; sweat gland
Abstract:
Multiple transthyretin (TTR) mutations have recently been identified and implicated in the development of familial systemic amyloidoses, but early diagnosis of these disorders is still largely unresolved. We investigated the presence and tissue distribution of TTR-derived amyloid in skin biopsies of a 59-year-old woman carrying the 'Hungarian-type' mutation of TTR (Asp18Gly). Clinical symptoms involved severe central nervous system dysfunction without signs of polyneuropathy, also referred to as the 'central form' of TTR-related systemic amyloidosis. Skin biopsy was also evaluated as a tool in order to diagnose this type of TTR amyloidosis. Biopsy samples were collected from the infra-axillary region. Light microscopy using Congo red and polarized light was used to diagnose amyloid deposits. Subsequently, electron microscopic analysis was performed to correlate the amyloid deposits with vicinal dermal structures. The amyloid class was determined by means of immunocytochemistry. TTR amyloid was primarily localized to lymphatic microvessels in the present case, whereas arterioles were devoid of TTR amyloid deposits. In addition, the well- known association of TTR amyloid with neural structures along the erector pilorum and around the sebaceous and serosal (sweat) glands was also evident. Electron microscopic analysis of amyloid deposits revealed characteristic amyloid fibrils that were irregular in shape, and exhibited a heterogeneous density and a random deposition pattern. Immunocytochemistry confirmed the cutaneous accumulation of TTR amyloid. In conclusion, amyloid deposits were abundantly present in the skin of a patient with 'Hungarian-type' TTR amyloidosis; skin biopsy seems to be appropriate for the diagnosis of this disorder. We showed that besides the erector pilorum, sweat glands and nerve terminals, lymphatic microvessels are also severely infiltrated by TTR amyloid. Whether these pathological alterations can exclusively be found in 'Hungarian-type' TTR amyloidosis should still be investigated. If such changes are not specific for the Asp18Gly mutation, they may be considered as diagnostic markers for 'central' TTR amyloid disorders.
