Figure 4. Loss of Large Myelinated Fibers and Onion-Bulbs in Dorsal Lumbar Rootlets of Chronic Immune Sensory Polyradiculopathy (CISP)–Plus.

Dorsal lumbar rootlet biopsies (A.a, B.a, C.a, D.a) and their corresponding myelinated fiber histograms (A.b, B.b, C.b, D.b) from a normal control (A) and from 3 patients with CISP-plus (B–D). The sections are methylene blue–stained epoxy preparations. The control biopsy (A) and histogram shows a normal bimodal size distribution. The CISP-plus biopsies are arranged in order from least (B) to most severely (D) affected. Note that in all 3 CISP-plus rootlet biopsies, the density of myelinated fibers is preserved but the size distribution is altered with loss of large myelinated fibers and a relative increase in the number of small myelinated fibers. These findings are confirmed in the histograms with loss of large myelinated fiber peaks (at 8.5 μm on the control) and larger amplitudes of the small myelinated fiber peak (at 3.0 μm). Note the frequent onion-bulbs (arrowheads) as well as the demyelinated axons surrounded by onion-bulbs (arrows) in (C) and (D). The loss of large myelinated sensory fibers demonstrated here correlates well with the clinical syndrome of gait ataxia. The severe pathologic findings from dorsal roots in CISP-plus are similar to those found in CISP rootlet biopsies. Morphometric analysis showed the mean myelinated fiber density (MF/mm²) of 3 dorsal rootlets in CISP-plus was 16,556/mm² (SD ± 5,917/mm²) and was similar to the densities of CISP and controls dorsal root biopsies. Individual densities were as follows: (B) 21,218, (C) 18,552, and (D) 9,899/mm². The 3 normal dorsal rootlet control biopsies had a mean MF density of 16,700/mm² (SD +/1,200/mm²) and 3 CISP dorsal rootlet biopsies had a mean MF density of 14,300/mm² (SD ± 1,850/mm²).