Dorsal root ganglia volume differentiates schwannomatosis and neurofibromatosis 2

Dorsal root ganglion magnetic resonance imaging biomarker correlations with pain in Fabry disease

Fabry disease is a rare monogenetic, X-linked lysosomal storage disorder with neuropathic pain as one characteristic symptom. Impairment of the enzyme alpha-galactosidase A leads to an accumulation of globotriaosylceramide in the dorsal root ganglia. Here, we investigate novel dorsal root ganglia MR imaging biomarkers and their association with Fabry genotype and pain phenotype. In this prospective study, 89 Fabry patients were examined using a standardized 3 T MRI protocol of the dorsal root ganglia. Fabry pain was assessed through a validated Fabry pain questionnaire. The genotype was determined by diagnostic sequencing of the alpha-galactosidase A gene. MR imaging end-points were dorsal root ganglia volume by voxel-wise morphometric analysis and dorsal root ganglia T2 signal. Reference groups included 55 healthy subjects and Fabry patients of different genotype categories without Fabry pain. In patients with Fabry pain, T2 signal of the dorsal root ganglia was increased by +39.2% compared to healthy controls (P = 0.001) and by +29.4% compared to painless Fabry disease (P = 0.017). This effect was pronounced in hemizygous males (+40.7% compared to healthy; P = 0.008 and +29.1% compared to painless; P = 0.032) and was consistently observed across the genotype spectrum of nonsense (+38.1% compared to healthy, P < 0.001) and missense mutations (+39.2% compared to healthy; P = 0.009). T2 signal of dorsal root ganglia and globotriaosylsphingosine levels were the only independent predictors of Fabry pain (P = 0.047; P = 0.002). Volume of dorsal root ganglia was enlarged by +46.0% in Fabry males in the nonsense compared to missense genotype category (P = 0.005) and by +34.5% compared to healthy controls (P = 0.034). In painful Fabry disease, MRI T2 signal of dorsal root ganglia is increased across different genotypes. Dorsal root ganglion MRI T2 signal as a novel in vivo imaging biomarker may help to better understand whether Fabry pain is modulated or even caused by dorsal root ganglion pathology.

Dorsal Root Ganglia Volume—Normative Values, Correlation with Demographic Determinants and Reliability of Three Different Methods of Volumetry

Background: Dorsal root ganglia (DRG) volume assessment by MR-Neurography (MRN) has evolved to an important imaging marker in the diagnostic workup of various peripheral neuropathies and pain syndromes. The aim of this study was (1) to assess normal values of DRG volume and correlations with demographic determinants and (2) to quantify the inter-reader and inter-method reliability of three different methods of DRG volumetry. Methods: Sixty healthy subjects (mean age: 59.1, range 23–79) were examined using a 3D T2-weighted MRN of the lumbosacral plexus at 3 Tesla. Normal values of DRG L3 to S2 were obtained after exact volumetry based on manual 3D segmentation and correlations with demographic variables were assessed. For the assessment of inter-reader and inter-method reliability, DRG volumes in a subset of 25 participants were measured by two independent readers, each applying (1) exact volumetry based on 3D segmentation, (2) axis-corrected, and (3) non-axis-corrected volume estimation. Intraclass correlation coefficients were reported and the Bland–Altman analysis was conducted. Results: Mean DRG volumes ranged from 124.8 mm3 for L3 to 323.3 mm3 for S1 and did not differ between right and left DRG. DRG volume (mean of L3 to S1) correlated with body height (r = 0.42; p = 0.0008) and weight (r = 0.34; p = 0.0087). DRG of men were larger than of women (p = 0.0002); however, no difference remained after correction for body height. Inter-reader reliability was high for all three methods but best for exact volumetry (ICC = 0.99). While axis-corrected estimation was not associated with a relevant bias, non-axis-corrected estimation systematically overestimated DRG volume by on average of 15.55 mm3 (reader 1) or 18.00 mm3 (reader 2) when compared with exact volumetry. Conclusion: The here presented normal values of lumbosacral DRG volume and the correlations with height and weight may be considered in future disease specific studies and possible clinical applications. Exact volumetry was most reliable and should be considered the gold standard. However, the reliability of axis-corrected and non-axis-corrected volume estimation was also high and might still be sufficient, depending on the degree of the required measurement accuracy.

Dorsal Root Ganglion Volumetry by MR Gangliography

BACKGROUND AND PURPOSE

Dorsal root ganglion MR imaging (MR gangliography) is increasingly gaining clinical-scientific relevance. However, dorsal root ganglion morphometry by MR imaging is typically performed under the assumption of ellipsoid geometry, which remains to be validated.

MATERIALS AND METHODS

Sixty-four healthy volunteers (37 [57.8%] men; mean age, 31.5 [SD, 8.3] years) underwent MR gangliography of the bilateral L4-S2 levels (3D-T2WI TSE spectral attenuated inversion recovery-sampling perfection with application-optimized contrasts by using different flip angle evolution, isotropic voxels = 1.1 mm³, TE = 301 ms). Ground truth dorsal root ganglion volumes were bilaterally determined for 96 dorsal root ganglia (derivation cohort) by expert manual 3D segmentation by 3 independent raters. These ground truth dorsal root ganglion volumes were then compared with geometric ellipsoid dorsal root ganglion approximations as commonly practiced for dorsal root ganglion morphometry. On the basis of the deviations from ellipsoid geometry, improved volume estimation could be derived and was finally applied to a large human validation cohort (510 dorsal root ganglia).

RESULTS

Commonly used equations of ellipsoid geometry underestimate true dorsal root ganglion volume by large degrees (factor = 0.42-0.63). Ground truth segmentation enabled substantially optimizing dorsal root ganglion geometric approximation using its principal axes lengths by deriving the dorsal root ganglion volume term of [Formula: see text]. Using this optimization, the mean volumes of 510 lumbosacral healthy dorsal root ganglia were as follows: L4: 211.3 (SD, 52.5) mm³, L5: 290.7 (SD, 90.9) mm³, S1: 384.2 (SD, 145.0) mm³, and S2: 192.4 (SD, 52.6) mm³. Dorsal root ganglion volume increased from L4 to S1 and decreased from S1 to S2 (P < .001). Dorsal root ganglion volume correlated with subject height (r = . 22, P < .001) and was higher in men (P < .001).

CONCLUSIONS

Dorsal root ganglion volumetry by measuring its principal geometric axes on MR gangliography can be substantially optimized. By means of this optimization, dorsal root ganglion volume distribution was estimated in a large healthy cohort for the clinically most relevant lumbosacral levels, L4-S2.

Spatial Distribution and Long-Term Alterations of Peripheral Nerve Lesions in Schwannomatosis

Purpose To examine the spatial distribution and long-term alterations of peripheral nerve lesions in patients with schwannomatosis by in vivo high-resolution magnetic resonance neurography (MRN). Methods In this prospective study, the lumbosacral plexus as well as the right sciatic, tibial, and peroneal nerves were examined in 15 patients diagnosed with schwannomatosis by a standardized MRN protocol at 3 Tesla. Micro-, intermediate- and macrolesions were assessed according to their number, diameter and spatial distribution. Moreover, in nine patients, peripheral nerve lesions were compared to follow-up examinations after 39 to 71 months. Results In comparison to intermediate and macrolesions, microlesions were the predominant lesion entity at the level of the proximal (p < 0.001), mid- (p < 0.001), and distal thigh (p < 0.01). Compared to the proximal calf level, the lesion number was increased at the proximal (p < 0.05), mid- (p < 0.01), and distal thigh level (p < 0.01), while between the different thigh levels, no differences in lesion numbers were found. In the follow-up examinations, the lesion number was unchanged for micro-, intermediate and macrolesions. The diameter of lesions in the follow-up examination was decreased for microlesions (p < 0.01), not different for intermediate lesions, and increased for macrolesions (p < 0.01). Conclusion Microlesions represent the predominant type of peripheral nerve lesion in schwannomatosis and show a rather consistent distribution pattern in long-term follow-up. In contrast to the accumulation of nerve lesions, primarily in the distal nerve segments in NF2, the lesion numbers in schwannomatosis peak at the mid-thigh level. Towards more distal portions, the lesion number markedly decreases, which is considered as a general feature of other types of small fiber neuropathy.

Long-term Follow-up and Histological Correlation of Peripheral Nervous System Alterations in Neurofibromatosis Type 2

Purpose

To examine long-term alterations of the dorsal root ganglia (DRG) and the peripheral nerve in patients with neurofibromatosis type 2 (NF2) by in vivo high-resolution magnetic resonance neurography (MRN) and their correlation to histology.

Methods

In this prospective study the lumbosacral DRG, the right sciatic, tibial, and peroneal nerves were examined in 6 patients diagnosed with NF2 and associated polyneuropathy (PNP) by a standardized MRN protocol at 3 T. Volumes of DRG L3–S2 as well as peripheral nerve lesions were assessed and compared to follow-up examinations after 14–100 months. In one patient, imaging findings were further correlated to histology.

Results

Follow-up MRN examination showed a non-significant increase of volume for the DRG L3: +0.41% (p = 0.10), L4: +22.41% (p = 0.23), L5: +3.38% (p = 0.09), S1: +10.63% (p = 0.05) and S2: +1.17% (p = 0.57). Likewise, peripheral nerve lesions were not significantly increased regarding size (2.18 mm² vs. 2.15 mm², p = 0.89) and number (9.00 vs. 9.33, p = 0.36). Histological analyses identified schwannomas as the major correlate of both DRG hyperplasia and peripheral nerve lesions. For peripheral nerve microlesions additionally clusters of onion-bulb formations were identified.

Conclusion

Peripheral nervous system alterations seem to be constant or show only a minor increase in adult NF2. Thus, symptoms of PNP may not primarily attributed to the initial schwannoma growth but to secondary long-term processes, with symptoms only occurring if a certain threshold is exceeded. Histology identified grouped areas of Schwann cell proliferations as the correlate of DRG hyperplasia, while for peripheral nerve lesions different patterns could be found.

Dorsal Root Ganglion Morphometric Changes Under Oxaliplatin Treatment : Longitudinal Assessment by Computed Tomography

Purpose

Magnetic resonance neurography (MRN) can detect dorsal root ganglia (DRG) hypertrophy in patients with oxaliplatin-induced peripheral neuropathy (OXIPN) but is difficult to apply in clinical daily practice. Aims of this study were (i) to assess whether DRG volume is reliably measurable by routine computed tomography (CT) scans, (ii) to measure longitudinal changes in DRG during and after oxaliplatin administration and (iii) to assess correlation between DRG morphometry and individual oxaliplatin dose.

Methods

For comparison of MRN and CT measurements, CT scans of 18 patients from a previous MRN study were analyzed. For longitudinal assessment of DRG size under treatment, 96 patients treated with oxaliplatin between January and December 2014 were enrolled retrospectively. DRG volumetry was performed by analyzing routine CT scans, starting with the last scan before oxaliplatin exposure (t0) and up to four consecutive timepoints after initiation of oxaliplatin therapy (t1–t4) with the following median and ranges in months: 3.1 (0.4–4.9), 6.2 (5.3–7.8), 10.4 (8.2–11.9), and 18.4 (12.8–49.8).

Results

DRG volume measured in CT showed a moderately strong correlation with MRN (r = 0.51, p < 0.001) and a strong correlation between two consecutive CTs (r = 0.77, p < 0.001). DRG volume increased after oxaliplatin administration with a maximum at timepoint t2. Higher cumulative oxaliplatin exposure was associated with significantly higher absolute DRG volumes (p = 0.005). Treatment discontinuation was associated with a nonsignificant trend towards lower relative DRG volume changes (p = 0.08).

Conclusion

CT is a reliable method for continuous DRG morphometry; however, since no standardized assessment of OXIPN was performed in this retrospective study, correlations between DRG size, cumulative oxaliplatin dose and clinical symptoms in future prospective studies are needed to establish DRG size as a potential OXIPN biomarker.

Supplementary Information

The online version of this article (10.1007/s00062-021-01083-5) contains supplementary material, which is available to authorized users.

Surgical Management of Sporadic Peripheral Nerve Schwannomas in Adults: Indications and Outcome in a Single Center Cohort

Simple Summary

Peripheral nerve sheath tumors are associated with significant morbidity. Clinical presentation, tumor location, and therapeutic strategies are variable. We aim to provide high-quality data concerning the results of interdisciplinary operative approaches for surgical resection of schwannomas. Understanding the anatomical and functional challenges of surgical interventions in the peripheral nervous system can help to enhance the outcomes of these therapies. We aim to highlight the need for interdisciplinarity and provide evidence for both excellent functional outcomes, as well as improved quality of life for patients undergoing sporadic schwannoma surgery.

Abstract

Most sporadic peripheral nerve sheath tumors in adults are schwannomas. These tumors usually present with significant pain but can also cause neurological deficits. Symptomatology is diverse, and successful surgical interventions demand interdisciplinarity. We retrospectively reviewed 414 patients treated between 2006 and 2017 for peripheral nerve sheath tumors. We analyzed clinical signs, symptoms, histology, and neurological function in the cohort of adult patients with schwannomas without a neurocutaneous syndrome. In 144 patients, 147 surgical interventions were performed. Mean follow-up was 3.1 years. The indication for surgery was pain (66.0%), neurological deficits (23.8%), significant tumor growth (8.8%), and suspected malignancy (1.4%). Complete tumor resection was achieved on 136/147 occasions (92.5%). The most common location of the tumors was intraspinal (49.0%), within the cervical neurovascular bundles (19.7%), and lower extremities (10.9%). Pain and neurological deficits improved significantly (p ≤ 0.003) after 131/147 interventions (89.1%). One patient had a persistent decrease in motor function after surgery. Complete resection was possible in 67% of recurrent tumors, compared to 94% of primary tumors. There was a significantly lower chance of complete resection for schwannomas of the cervical neurovascular bundle as compared to other locations. The surgical outcome of sporadic schwannoma surgery within the peripheral nervous system is very favorable in experienced peripheral nerve surgery centers. Surgery is safe and effective and needs a multidisciplinary setting. Early surgical resection in adult patients with peripheral nerve sheath tumors with significant growth, pain, neurological deficit, or suspected malignancy is thus recommended.

Neurofibromatosis type 2 and related disorders

PURPOSE OF REVIEW

Neurofibromatosis type 2 (NF2) is a schwannoma predisposition syndrome, alongside schwannomatosis related to germline LZTR1 and SMARCB1 pathogenic variants. This review highlights their overlapping phenotypes, new insight into NF2 phenotype and treatment outcomes.

RECENT FINDINGS

Mosaic NF2 is more prevalent than previously thought. Use of next-generation sequencing and tumour testing is needed to differentiate mosaic NF2 and schwannomatosis. Developing NF2 phenotypic insights include vasculopathy with brainstem infarction and vessel stenosis; focal cortical dysplasia in severe phenotypes; swallowing/speech difficulties and continued debate into malignancy in NF2. Proposed are: use of visual evoked potentials to monitor optic nerve sheath meningioma; potential routine magnetic resonance angiogram in adolescence and a genetic score to cohort patients with similar pathogenic_variants, for natural history/treatment outcome studies. Cohort studies found survival analysis to hearing loss and unilateral visual loss in severe mutation groups was 32 and 38 years; active management gave better outcomes than surveillance in spinal ependymoma; gamma knife, bevacizumab and hearing preservation surgery maintained or improved short-term hearing in selected patients, and gamma knife had a good long-term tumour control in mild patients with small tumours.

SUMMARY

Further long-term outcome studies are needed comparing similar severity patients to allow informed decision making.

Regional Differences in Tight Junction Protein Expression in the Blood-DRG Barrier and Their Alterations after Nerve Traumatic Injury in Rats

The nervous system is shielded by special barriers. Nerve injury results in blood–nerve barrier breakdown with downregulation of certain tight junction proteins accompanying the painful neuropathic phenotype. The dorsal root ganglion (DRG) consists of a neuron-rich region (NRR, somata of somatosensory and nociceptive neurons) and a fibre-rich region (FRR), and their putative epi-/perineurium (EPN). Here, we analysed blood–DRG barrier (BDB) properties in these physiologically distinct regions in Wistar rats after chronic constriction injury (CCI). Cldn5, Cldn12, and Tjp1 (rats) mRNA were downregulated 1 week after traumatic nerve injury. Claudin-1 immunoreactivity (IR) found in the EPN, claudin-19-IR in the FRR, and ZO-1-IR in FRR-EPN were unaltered after CCI. However, laser-assisted, vessel specific qPCR, and IR studies confirmed a significant loss of claudin-5 in the NRR. The NRR was three-times more permeable compared to the FRR for high and low molecular weight markers. NRR permeability was not further increased 1-week after CCI, but significantly more CD68⁺ macrophages had migrated into the NRR. In summary, NRR and FRR are different in naïve rats. Short-term traumatic nerve injury leaves the already highly permeable BDB in the NRR unaltered for small and large molecules. Claudin-5 is downregulated in the NRR. This could facilitate macrophage invasion, and thereby neuronal sensitisation and hyperalgesia. Targeting the stabilisation of claudin-5 in microvessels and the BDB barrier could be a future approach for neuropathic pain therapy.

Distinctive low epidermal nerve fiber density in schwannomatosis patients provides a major parameter for diagnosis and differential diagnosis

Schwannomatosis and neurofibromatosis type 2 (NF2) are two distinct neuro‐genetic tumor predisposition disorders, which, however, share some clinical and genetic features. While germline mutations in the NF2 gene are only found in NF2, a majority of schwannomatosis patients have germline mutations in the SMARCB1 or LZTR1 genes. The overlapping clinical phenotypes pose a serious challenge in differential diagnosis and in risk stratification of these two entities which is further complicated by frequent mosaicism in both disorders. Chronic neuropathic pain which is a typical consequence of small fiber neuropathy, is characteristic for schwannomatosis. By contrast, NF2 patients do not have chronic pain but may have moderate to severe sensory deficits and paresis which are not characteristic for schwannomatosis. In the present study, we determined intraepidermal nerve fiber density (IEND) in skin biopsies of 34 clinically ascertained schwannomatosis and 25 NF2 patients. In the NF2 group, 11/25 (44%) presented with IEND below the age‐ and gender‐matched bottom 5% normative reference IEND. In contrast, nearly all (33/34 = 97%) schwannomatosis patients showed IEND below or on the bottom 5% normative reference. The reduction of IEND in schwannomatosis patients was age‐independent. Paired t‐test revealed no difference between the NF2‐IEND and the corresponding bottom 5% normative reference (P = 0.98). By contrast, IEND in the schwannomatosis patients were highly significantly lower than the corresponding 5% normative reference IEND (P < 0.0001). In addition, the difference between the IEND of our patients and the 5% lowest normative reference IEND was highly significantly larger in schwannomatosis patients than in NF2 patients (P < 0.0001). IEND of our patients did not correlate with neither the presence nor types of germline mutations in neither the NF2 nor the LZTR1 gene. In conclusion, schwannomatosis patients have marked low IEND which provides a major parameter for diagnosis and differential diagnosis.

Peripheral nervous system alterations in infant and adult neurofibromatosis type 2

OBJECTIVE

To examine the involvement of dorsal root ganglia and peripheral nerves in children with neurofibromatosis type 2 compared to healthy controls and symptomatic adults by in vivo high-resolution magnetic resonance neurography.

METHODS

In this prospective multicenter study, the lumbosacral dorsal root ganglia and sciatic, tibial, and peroneal nerves were examined in 9 polyneuropathy-negative children diagnosed with neurofibromatosis type 2 by a standardized magnetic resonance neurography protocol at 3T. Volumes of dorsal root ganglia L3 to S2 and peripheral nerve lesions were assessed and compared to those of 29 healthy children. Moreover, dorsal root ganglia volumes and peripheral nerve lesions were compared to those of 14 adults with neurofibromatosis type 2.

RESULTS

Compared to healthy controls, dorsal root ganglia hypertrophy was a consistent finding in children with neurofibromatosis type 2 (L3 +255%, L4 +289%, L5 +250%, S1 +257%, and S2 +218%, p < 0.001) with an excellent diagnostic accuracy. Moreover, peripheral nerve lesions occurred with a high frequency in those children compared to healthy controls (18.89 ± 11.11 vs 0.90 ± 1.08, p < 0.001). Children and adults with neurofibromatosis type 2 showed nonsignificant differences in relative dorsal root ganglia hypertrophy rates (p = 0.85) and peripheral nerve lesions (p = 0.28).

CONCLUSIONS

Alterations of peripheral nerve segments occur early in the course of neurofibromatosis type 2 and are evident even in children not clinically affected by peripheral polyneuropathy. While those early alterations show similar characteristics compared to adults with neurofibromatosis type 2, the findings of this study suggest that secondary processes might be responsible for the development and severity of associated polyneuropathy.

Quantitative MR neurography biomarkers in 5q-linked spinal muscular atrophy

OBJECTIVE

To characterize and quantify peripheral nerve lesions and muscle degeneration in clinically, genetically, and electrophysiologically well-classified, nonpediatric patients with 5q-linked spinal muscular atrophy (SMA) by high-resolution magnetic resonance neurography (MRN).

METHODS

Thirty-one adult patients with genetically confirmed 5q-linked SMA types II, IIIa, and IIIb and 31 age- and sex-matched healthy volunteers were prospectively investigated. All patients received neurologic, physiotherapeutic, and electrophysiologic assessments. MRN at 3.0T with anatomic coverage from the lumbosacral plexus and proximal thigh down to the tibiotalar joint was performed with dual-echo 2D relaxometry sequences with spectral fat saturation and a 3D T2-weighted inversion recovery sequence. Detailed quantification of nerve injury by morphometric and microstructural MRN markers and qualitative classification of fatty muscle degeneration were conducted.

RESULTS

Established clinical scores and compound muscle action potentials discriminated well between the 3 SMA types. MRN revealed that peroneal and tibial nerve cross-sectional area (CSA) at the thigh and lower leg level as well as spinal nerve CSA were markedly decreased throughout all 3 groups, indicating severe generalized peripheral nerve atrophy. While peroneal and tibial nerve T2 relaxation time was distinctly increased at all analyzed anatomic regions, the proton spin density was clearly decreased. Marked differences in fatty muscle degeneration were found between the 3 groups and for all analyzed compartments.

CONCLUSIONS

MRN detects and quantifies peripheral nerve involvement in SMA types II, IIIa, and IIIb with high sensitivity in vivo. Quantitative MRN parameters (T2 relaxation time_, proton spin density, CSA) might serve as novel imaging biomarkers in SMA to indicate early microstructural nerve tissue changes in response to treatment.

Human Dorsal Root Ganglia

Sensory neurons with cell bodies situated in dorsal root ganglia convey information from external or internal sites of the body such as actual or potential harm, temperature or muscle length to the central nervous system. In recent years, large investigative efforts have worked toward an understanding of different types of DRG neurons at transcriptional, translational, and functional levels. These studies most commonly rely on data obtained from laboratory animals. Human DRG, however, have received far less investigative focus over the last 30 years. Nevertheless, knowledge about human sensory neurons is critical for a translational research approach and future therapeutic development. This review aims to summarize both historical and emerging information about the size and location of human DRG, and highlight advances in the understanding of the neurochemical characteristics of human DRG neurons, in particular nociceptive neurons.