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BACKGROUND AND PURPOSE We aimed to test the clinical utility of the leg:thigh intraepidermal nerve-fiber (IENF) density ratio as a parameter to discriminate between length-dependent small-fiber neuropathy (SFN) and small-fiber sensory ganglionopathy (SFSG) in subjects with signs and symptoms of small-fiber pathology. METHODS We retrospectively evaluated thigh and leg IENF density in 314 subjects with small-fiber pathology (173 with distal symmetrical length-dependent SFN and 141 with non-length-dependent SFSG). A group of 288 healthy subjects was included as a control group. The leg:thigh IENF density ratio was calculated for all subjects. We used receiver operating characteristic curve analyses to assess the ability of this parameter to discriminate between length-dependent SFN and SFSG, and the decision curve analysis to estimate its net clinical benefit. RESULTS In patients with neuropathy, the mean IENF density was 14.8 ± 6.8/mm at the thigh (14.0 ± 6.9/mm in length-dependent SFN and 15.9 ± 6.7/mm in patients with SFSG) and 7.5 ± 4.5/mm at the distal leg (5.4 ± 3.2/mm in patients with length-dependent SFN and 10.1 ± 4.6/mm in patients with SFSG). The leg:thigh IENF density ratio was significantly (P < 0.01) lower in patients with length-dependent SFN (0.44 ± 0.23) compared with patients with SFSG (0.68 ± 0.28). The area under the curve of the receiver operating characteristic analysis to discriminate between patients with length-dependent SFN and SFSG was 0.79. The decision curve analysis demonstrated the clinical utility of this parameter. CONCLUSIONS The leg:thigh IENF ratio represents a valuable tool in the differential diagnosis between SFSG and length-dependent SFN.

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Background and purpose: Autosomal Recessive Hereditary Spastic Paraplegia with Thin Corpus Callosum (AR-HSPTCC) is a clinically and genetically heterogeneous complicated form of spastic paraplegia. Two AR-HSPTCC loci have been assigned to chromosome 15q13-15 (SPG11) and chromosome 8p12-p11.21 respectively. Mutations in the SPG11 gene, encoding the spatacsin protein, have been found in the majority of SPG11 families. In this study, involvement of the SPG11 or 8p12-p11.21 loci was investigated in five Italian families, of which four consanguineous. Methods: Families were tested for linkage to the SPG11 or 8p12-p11.21 loci and the SPG11 gene was screened in all the affected individuals. Results: Linkage was excluded in the four consanguineous families. In the only SPG11-linked family the same homozygous haplotype 4.2 cM across the SPG11 locus was shared by all the three affected siblings. A novel c.2608A>G mutation predicted to affect the splicing was found in exon 14 of the SPG11 gene. Discussion: This collection of families contributes to highlight the intra and inter locus heterogeneity in AR-HSPTCC, already remarked in previous reports. In particular, it confirms heterogeneity amongst Italian families and reports a new mutation predicted to affect splicing in the spatacsin gene.