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Washington University Experience | PERIPHERAL NEUROPATHY | 20 PSEUDO-ONION BULBS | 1D Case 1 Denouement
Denouement: I find this a particularly difficult case to place precisely and confidently in a single OB/POB category and I have included it here to discuss it in more detail. First, active axonal degeneration is not identified in this case which is surprising in light of the clinical presentation. This case really looks like a true onion bulb neuropathy, likely hereditary, since each myelinated axon in each fascicle is involved to the same extent. However, the overall appearance of the nerve background including unmyelinated axons appears most consistent with an axonal degeneration. Could it be a fulminant case of CIDP? Such cases often have inflammation, lacking in this case, macrophage mediated demyelination (but only a few myelinated axons are residual), and variation between fascicles (uniform in this case). Nonetheless, it is surprising in a hereditary onion bulb neuropathy for there to be no demyelinated or remyelinating axons. In typical hereditary onion-bulb neuropathies the Schwann cell lamellae are delicate and have only a few unmyelinated axons within them. In this case the leaves of the lamellae are thicker, more coarse and more resemble bands of Büngner. In true genetically characterized hereditary onion bulb cases exhibiting denervated or “obsolete” onion bulbs there is typically more axon loss and empty endoneurial space and usually residual demyelination. This case was sent from an outside source in consultation and there is no evidence that a panel of gene alterations was performed, which would have been done if the case was current. Thus, it “Is what it is” but a spectacular case.
