Seeing purple

Porphyric neuropathy

Porphyric neuropathy often poses a diagnostic dilemma; it is typically associated with the hepatic porphyrias, characterized by acute life-threatening attacks of neurovisceral symptoms that mimic a range of acute medical and psychiatric conditions. The development of acute neurovisceral attacks is responsive to environmental factors, including drugs, hormones, and diet. This chapter reviews the clinical manifestations, genetics, pathophysiology, and mechanisms of neurotoxicity of the acute hepatic porphyrias. While the etiology of the neurological manifestations in the acute porphyrias remains undefined, the main hypotheses include toxicity of porphyrin precursors and deficiency of heme synthesis. These hypotheses will be discussed with reference to novel experimental models of porphyric neuropathy.

Purple pigments: the pathophysiology of acute porphyric neuropathy

The porphyrias are inherited metabolic disorders arising from disturbance in the haem biosynthesis pathway. The neuropathy associated with acute intermittent porphyria (AIP) occurs due to mutation involving the enzyme porphobilinogen deaminase (PBGD) and is characterised by motor-predominant features. Definitive diagnosis often encompasses a combination of biochemical, enzyme analysis and genetic testing, with clinical neurophysiological findings of a predominantly motor axonal neuropathy. Symptomatic and supportive treatment are the mainstays during an acute attack. If administered early, intravenous haemin may prevent progression of neuropathy. While the pathophysiology of AIP neuropathy remains unclear, axonal dysfunction appears intrinsically linked to the effects of neural energy deficits acquired through haem deficiency coupled to the neurotoxic effects of porphyrin precursors. The present review will provide an overview of AIP neuropathy, including discussion of recent advances in understanding developed through neurophysiological approaches that have further delineated the pathophysiology of axonal degeneration.