Difference between revisions of "6° Clinical case: Facial onset sensory and motor neuronopathy"

Trigeminal and extra-trigeminal sensory function were assessed: touch was studied with a cotton ball, vibration with a tuning fork (128 Hz), and pin-prick sensation with a wooden cocktail stick. Gait impairment and muscle strength were assessed with the Medical Research Council score. We were also asked to report dysautonomic symptoms. The patient underwent laboratory tests, including tests to rule out identifiable causes of trigeminal neuropathy: autoantibody assays to detect connective tissue disease (antinuclear antibodies, anti-double stranded DNA, antinuclear extractable antigens, including anti Sm, anti RNP, anti Scl70 and anti -phospholipids, antineutrophil cytoplasmic antibodies and anti Ro/SSA and anti-La/SSB for Sjögren's disease).

Serum genetic testing for Kennedy disease, cholesterol esters and low serum cholesterol for Tangieri disease, glycosphingolipid accumulation for Fabry disease, and serum angiotensin converting enzyme for neurosarcoidosis. Of course, gadolinium-enhanced magnetic resonance imaging (MRI) of the brain and spinal cord was also performed.

Supraorbital nerve biopsies were performed by an experienced plastic surgeon. Samples fixed with 2% glutaraldehyde in phosphate buffered saline (PBS) at 4°C. Samples were post-fixed in 1% osmium tetroxide in veronal acetate buffer (pH 7.4) for 1 hour at 25°C, stained with uranyl acetate (5 mg/ml) for 1 hour at 25°C C, dehydrated in acetone and incorporated in Epon 812 (EMbed 812, Electron Microscopy Science, Hatfield, PA, USA).

Semithin sections were stained with toluidine blue for light microscopic evaluation. Ultrathin sections from tissue blocks in the correct orientation, post-stained with uranyl acetate and lead hydroxide, were examined with a Morgagni 268D transmission electron microscope (FEI, Hillsboro, OR, USA). Digital images were analyzed with AnalySIS software (SIS) and all myelinated and unmyelinated structures were identified and measured. Fiber densities were calculated and expressed as average number of fibers/mm².

==== Trigeminal neurophysiology ====

Trigeminal motor evoked potentials were tested by transcranial magnetic stimulation,<ref>Cruccu G, Berardelli A, Inghilleri M, Manfredi M. Functional organization of the trigeminal motor system in man. A neurophysiological study. Brain. 1989;112:1333–1350. doi: 10.1093/brain/112.5.1333.</ref> the temporal H reflex, evaluating the Aα fiber (Ia fiber) in the monosynaptic trigeminal reflex,<ref>Cruccu G, Truini A, Priori A. Excitability of the human trigeminal motoneuronal pool and interactions with other brainstem reflex pathways. J Physiol. 2001;531:559–571. doi: 10.1111/j.1469-7793.2001.0559i.x.</ref> the early components of the blink reflex (R1) after electrical stimulation of the supraorbital nerve, and the masseter inhibitory reflex (SP1) after stimulation of the mental nerve, assessing the fibers <math>A\beta</math>.<ref>Valls-Solé J. Neurophysiological assessment of trigeminal nerve reflexes in disorders of central and peripheral nervous system. Clin Neurophysiol. 2005;116:2255–2265. doi: 10.1016/j.clinph.2005.04.020.</ref> Laser-evoked potentials (LEP) were also recorded to study nociceptors <math>A\delta</math>(<math>A\delta</math>-LEP) and unmyelinated fiber heat receptors (C-LEP).<ref>Cruccu G, Pennisi E, Truini A, Iannetti GD, Romaniello A, Le Pera D, De Armas L, Leandri M, Manfredi M, Valeriani M. Unmyelinated trigeminal pathways as assessed by laser stimuli in humans. Brain. 2003;126:2246–2256. doi: 10.1093/brain/awg227.</ref> The neurophysiological tests have adhered to the technical requirements issued by the International Federation of Clinical Neurophysiology.<ref>Kimura J, editor. Peripheral Nerve Diseases, Handbook of Clinical Neurophysiology.Amsterdam: Elsevier; 2006.</ref><ref>Cruccu G, Aminoff MJ, Curio G, Guerit JM, Kakigi R, Mauguiere F, Rossini PM, Treede RD, Garcia-Larrea L. Recommendations for the clinical use of somatosensory-evoked potentials. Clin Neurophysiol. 2008;119:1705–1719. doi: 10.1016/j.clinph.2008.03.016.</ref>

==== Significant results of the investigations ====

Motor evoked potentials from transcranial magnetic stimulation and the temporalis muscle H reflex yielded normal results; in contrast, reflex recordings showed severe abnormalities: the first response to become absent bilaterally was the early masseter inhibitory reflex (ES1) after mental nerve stimulation and the early blink reflex (R1). While <math>A\delta</math> fiber-mediated LEPs were often abnormal (but less impaired than early trigeminal reflexes), unmyelinated C-fiber-mediated C-LEPs were normal. These patterns of neurophysiological abnormalities generally suggested that the disease progressed from larger to smaller afferent fibers. <blockquote>The one notable exception was the normal temporal H reflex afferent-mediated by <math>A\alpha</math>. Both light and electron microscopy showed only Wallerian-like degeneration involving myelinated fibers, more severe for the large <math>A\beta</math> and small group <math>A\delta</math>, with no inflammatory changes.</blockquote>

=== '''Discussion''' ===

From the study by Cruccu et al.<ref name=":0">Cruccu G, Pennisi EM, Antonini G, Biasiotta A, di Stefano G, La Cesa S, Leone C, Raffa S, Sommer C, Truini A.Trigeminal isolated '''sensory''' neuropathy (TISN) and FOSMN syndrome: despite a dissimilar disease course do they share common pathophysiological mechanisms? BMC Neurol. 2014 Dec 19;14:248. doi: 10.1186/s12883-014-0248-2.PMID: 25527047 </ref> first of all it is deduced that despite detailed neurophysiological and morphometric investigations, no clinical, neurophysiological or neuropathological differences can be found between TISN and FOSMN, therefore, the two diseases could be pathophysiologically similar neuropathies of the type of dissociated neuropathies that completely spare the unmyelinated fibers as demonstrated by the biopsy exam. Light and electron microscopy in supraorbital nerve biopsy specimens from patients with TISN and those with FOSMN have shown variously severe axonal myelinated fiber loss, as others have reported in these patients.<ref>Lecky BR, Hughes RA, Murray NM. Trigeminal sensory neuropathy. A study of 22 cases. Brain. 1987;110:1463–1485. doi: 10.1093/brain/110.6.1463. </ref><ref name=":1">Vucic S, Tian D, Chong PS, Cudkowicz ME, Hedley-Whyte ET, Cros D. Facial onset sensory and motor neuronopathy (FOSMN syndrome): a novel syndrome in neurology. Brain. 2006;129:3384–3390. doi: 10.1093/brain/awl258.</ref> We extend these findings by providing quantitative data showing that trigeminal neuropathy affects fibers <math>A\beta</math> more severely than fibers<math>A\delta</math>. Evidence that nerve fiber damage progresses from the largest to the smallest fiber also comes from neurophysiological findings, which invariably show responses mediated by the impaired fiber <math>A\beta</math> even in the early stages of the disease. In contrast, <math>A\delta</math> fiber-mediated responses were much less impaired.

According to Cruccu et al.<ref name=":0" /> temporal sparing of the H reflex provides evidence that FOSMN primarily affects cell bodies.<ref name=":1" /><ref>Vucic S1, Stein TD, Hedley-Whyte ET, Reddel SR, Tisch S, Kotschet K, Cros D, Kiernan MC. FOSMN syndrome: novel insight into disease pathophysiology. Neurology. 2012;79:73–79. doi: 10.1212/WNL.0b013e31825dce13.</ref> A dissociated neuropathy that progressively affects larger and then smaller myelinated fibers should in theory severely impair a reflex mediated by <math>A\alpha</math> afferents from muscle spindles. Conversely, it spares the primary afferents from the trigeminal spindles because they travel in the motor rather than the sensory root. Equally important, rather than lying in the sensory ganglion, their cell bodies lie in the midbrain trigeminal nucleus.<ref>Collier TG, Lund JP. The effect of sectioning the trigeminal sensory root on the periodontally-induced jaw-opening reflex. J Dent Res. 1987;66:1533–1537. doi: 10.1177/00220345870660100401.</ref><ref>Dessem D, Taylor A. Morphology of jaw-muscle spindle afferents in the rat. J Comp Neurol. 1989;282:389–403. doi: 10.1002/cne.902820306.</ref> This unique anatomical feature also explains why mandibular tendon snapping (or jaw snapping) is spared in two other trigeminal neuropathies: Sjögren's syndrome and Kennedy's disease.<ref>Valls-Sole J, Graus F, Font J, Pou A, Tolosa ES. Normal proprioceptive trigeminal afferents in patients with Sjögren's syndrome and sensory neuronopathy. Ann Neurol. 1990;28:786–790. doi: 10.1002/ana.410280609. </ref><ref>Antonini G, Gragnani F, Romaniello A, Pennisi EM, Morino S, Ceschin V, Santoro L, Cruccu G: Sensory involvement in spinal-bulbar muscular atrophy (Kennedy's disease).''Muscle Nerve'' 2000; 23:252-258.</ref>

{{q2|Most likely the cause may not be iatrogenic|....... are we still sure we know everything?}}