On the nature of the peripheral nerve lesions associated with acute intermittent porphyria

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Abstract
Post-mortem study of 4 cases of acute intermittent porphyria included histological study of muscle.samples from the upper extremity, the ulnar and median nerves and the spinal cord with several spinal root ganglia. Only normal fibers or fibers undergoing Wallerian degeneration were found in the peripheral nerves and spinal roots. Segmental degeneration was not found in any specimen. Gross denervation of muscle was seen. The degeneration of the nerves was of the ''dying back'' type. Distal muscles in all cases showed more severe, longer standing denervation but interestingly enough the weakness, as assessed neurologically, was in all but one case considered to be most marked and earliest in the proximal muscle groups. Apparently in porphyria neuropathy the ''dying back'' occurs more or less irrespective of distance from the spinal cord and the size of the motor units determines the site of weakness. This study shows the primary defect to be present in motor neurons and secondarily the sensory cells are affected. Although a metabolic lesion in pathways concerned with energy transfer within the cell have been emphasized in other reports, the present study shows a selectivity of the process to anterior horn and spinal ganglia cells which suggests additional patho-genetic factors.