The neuropathologic features of adrenomyeloneuropathy (AMN) are reviewed by supplementing those few previously published cases with 5 additional cases collected over the years. The endocrine involvement in AMN is briefly presented to serve as a pathogenetic backdrop and to emphasize that most of the lesions in AMN, as in adreno-leukodystrophy (ALD), are noninflammatory in the traditional sense of the word. The myeloneuropathy is emphasized, but the dysmyelinative/inflammatory demyelinative lesions also are presented. The preponderance of available data indicates that the myeloneuropathy of AMN is a central-peripheral distal (dying-back) axonopathy, as was originally proposed. The severity of the myeloneuropathy does not appear to correlate with the duration or severity of endocrine dysfunction. Microglia are the dominant participating cells in the noninflammatory myelopathy. Abnormalities in the ALD gene, which encodes a peroxisomal ABC half-transporter, do not correlate with clinical phenotypes. The relationship of the gene product, ALDP, to the peroxisomal very long chain fatty acid (VLCFA) synthetase, the activity of which is deficient in ALD/AMN, is unclear. An ALD-knockout mouse model has developed axonal degeneration, particularly in spinal cord, and is therefore more reminiscent of AMN than ALD. We continue to postulate that the fundamental defect in the myeloneuropathy of AMN is an axonal or neuronal membrane abnormality perhaps due to the incorporation of VLCFA-gangliosides, which perturbs the membrane's microenvironment and leads to dysfunction and atrophy.

Adrenomyeloneuropathy (AMN), a disease of spinal cord, brain, adrenal, and testis, mostly affects men with spastic paraparesis or ataxia beginning in their second or third decade. The spinal cord displays bilateral, usually symmetrical, long tract degeneration particularly of the gracile tract in a "dying-back" pattern. The available data strongly indicate that the fundamental lesion in AMN is an axonopathy or neuronopathy. We compared lumbar dorsal root ganglia (DRG) from 3 AMN patients to 6 age-matched controls histologically, morphometrically, immunohistochemically, and ultrastructurally. There was no apparent neuronal loss, necrosis or apoptosis, nor obvious atrophy; nodules of Nageotte were sparse in both groups. The morphometric studies, however, did reveal neuronal atrophy with a decrease in the number of large neurons and a corresponding increase in neurons less than 2,000 microm2, especially in the 1,500-1,999 microm2 range. No consistent immunohistochemical differences were observed, and no specific cell type appeared to be lost. Many mitochondria in the AMN neurons demonstrated lipidic inclusions; this raises the possibility that, in addition to the well-known peroxisomal defect, impaired mitochondrial function may lead to a failure of ATP-dependent axoplasmic transport in AMN spinal tracts with consequent "dying-back" axonal degeneration. The observation that the DRG parent neurons of the degenerate gracile tracts in AMN undergo atrophy and do not display appreciable evidence of cell death, even at autopsy, provides a wide window of opportunity for the development of therapeutic strategies to combat or prevent this myeloneuropathy.

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