Unexpected nerve neuroimaging findings in Friedreich’s ataxia

Nerve ultrasound in CANVAS-spectrum disease: Reduced nerve size distinguishes genetically confirmed CANVAS from other axonal polyneuropathies

BACKGROUND AND AIMS

Ultrasound nerve cross-sectional area (CSA) of patients affected with axonal neuropathy usually shows normal value. Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) seems to represent an exception, showing smaller CSA, but previous reports did not test for biallelic RFC1 gene repeat expansions.

METHODS

We compared nerve CSA from CANVAS patients (tested positive for biallelic RFC1 gene repeat expansions) with the CSA from a group of patients with chronic idiopathic axonal polyneuropathy (CIAP) who tested negative for RFC1 gene repeat expansions, hereditary axonal neuropathy (Charcot-Marie-Tooth type 2, CMT2), and Friedreich ataxia (FRDA).

RESULTS

We enrolled 15 CANVAS patients (eight men, mean age 66.3 ± 11.5 years, mean disease duration 9.3 ± 4.1 years), affected with sensory axonal neuronopathy. Controls consisted of 13 CIAP (mean age 68.5 ± 12.8 years, seven men), seven CMT2 (mean age 47.9 ± 18.1 years, four men), 12 FRDA (mean age 33.7 ± 8.8, five men). Nerve ultrasound was performed at median, ulnar, sciatic, sural, and tibial nerves and brachial plexus, bilaterally. The nerve CSA from CANVAS patients was significantly smaller than the one from the other cohorts at several sites with significant and high accuracy at Receiver-operating characteristic (ROC) curve analyses. RFC1 AAGGG pentanucleotide expansion, disease duration, and disability did not correlate with CSA at any site, after Bonferroni correction.

INTERPRETATION

Decreased sonographic nerve sizes, in arms and legs, in patients with sensory neuropathy and normal motor conduction studies could point to CANVAS-spectrum disease and help guide appropriate genetic testing.

Nerve ultrasound in Friedreich's Ataxia: enlarged nerves as a biomarker of disease severity

OBJECTIVE

In Friedreich's ataxia research, the focus is on discovering treatments and biomarkers to assess disease severity and treatment effects. Our study examines high-resolution nerve ultrasound in these patients, seeking correlations with established clinical markers of disease severity.

METHOD

Ten patients with Friedreich's Ataxia underwent a comprehensive clinical assessment with established scales (SARA, FARS, mFARS, INCAT, ADL 0-36, IADL). Additionally, they underwent nerve conduction studies and high-resolution nerve ultrasound. Quantitative evaluation of nerve cross-sectional area, conducted at 24 nerve sites using high-resolution nerve ultrasound, was compared with data obtained from 20 healthy volunteers.

RESULTS

All the patients had a severe sensory axonal neuropathy. High-resolution nerve ultrasound showed significant increase, in cross sectional area, of median and ulnar nerves at the axilla and arm. The cumulative count of affected nerve sites was directly associated with clinical disability, as determined by SARA, FARS, mFARS, ADL 0-36, and INCAT score, while displaying an inverse correlation with IADL.

CONCLUSIONS

Our study shows that high-resolution ultrasound reveals notable nerve abnormalities, primarily in the upper limbs of patients diagnosed with Friedreich's Ataxia. The observed correlation between these nerve abnormalities and clinical disability scales indicates the potential use of this technique as a biomarker for evaluating disease severity and treatment effects.

SIGNIFICANCE

Nerve Ultrasound is a potential biomarker of disease severity in Friedreich's Ataxia.

Funktion und Struktur peripherer Nerven aus neuropädiatrischer Sicht: Wie klinische, neurophysiologische und Ultraschalluntersuchungen ergänzende diagnostische Informationen liefern

In der vorliegenden Übersicht wird dargestellt, wie sich klinisch neurophysiologische Methoden (Nervenleitgeschwindigkeit und Elektromyografie) und Ultraschalluntersuchungen (US) von peripheren Nerven bei der Abklärung von hereditären senso-motorischen Neuropathien (HMSN), der Friedreichschen Ataxie, erworbenen Neuropathien (am Beispiel von Diabetes mellitus) und traumatischen Nervenläsionen bei Kindern ergänzen können. Bei allen Formen der HMSN 1 kommt es zu einer Verlangsamung der Nervenleitgeschwindigkeit. Die Ultraschalluntersuchung zeigt nur bei HMSN1A eine deutlich vergrösserte Nervenquerschnittsfläche. Beim M. Friedreich können meist keine sensiblen Potentiale ausgelöst werden und die US-Resultate sind variabel. Bei traumatischen Nervenläsionen kann vor allem mithilfe der US-Untersuchung entschieden werden, ob eine operative Nervenrevision indiziert ist. Die erworbenen Neuropathien werden am Beispiel der diabetischen Neuropathie dargestellt. Die US- und die ENG Resultate sind oft abnorm, auch wenn klinisch keine Neuropathie-Symptome nachweisbar sind.

Peripheral nerve ultrasound in Friedreich ataxia

INTRODUCTION

Sensory impairment in Friedreich ataxia (FRDA) is generally accepted as being due to a ganglionopathy. The degree of contribution from axonal pathology remains a matter of debate. Nerve ultrasound may be able to differentiate these processes.

METHODS

The ultrasound cross-sectional area of median, ulnar, tibial, and sural nerves of 8 patients with FRDA was compared with 8 age- and gender-matched healthy controls and with reference values in our population.

RESULTS

The nerves of the patients with FRDA were significantly larger than those of healthy controls at all upper limb sites (P < 0.05) but not significantly different in the lower limbs.

DISCUSSION

Our findings add additional weight to the theory that dorsal root ganglionopathy is not the sole cause of peripheral sensory loss in FRDA. Peripheral neuropathic processes are also likely to play a role. Muscle Nerve 57: 852-856, 2018.