title: Trigeminal isolated sensory neuropathy (TISN) and FOSMN syndrome: despite a dissimilar disease course do they share common pathophysiological mechanisms?
abstract: BACKGROUND
  Patients presenting with bilateral trigeminal hypoesthesia may go on to have trigeminal isolated sensory neuropathy, a benign, purely trigeminal neuropathy, or facial-onset sensory motor neuronopathy (FOSMN), a malignant life-threatening condition. No diagnostic criteria can yet differentiate the two conditions at their onset. Nor is it clear whether the two diseases are distinct entities or share common pathophysiological mechanisms.
  
  
  METHODS
  Seeking pathophysiological and diagnostic information to distinguish these two conditions at their onset, in this neurophysiological and morphometric study we neurophysiologically assessed function in myelinated and unmyelinated fibres and histologically examined supraorbital nerve biopsy specimens with optic and electron microscopy in 13 consecutive patients with recent onset trigeminal hypoesthesia and pain.
  
  
  RESULTS
  The disease course distinctly differed in the 13 patients. During a mean 10 year follow-up whereas in eight patients the disease remained relatively stable, in the other five it progressed to possibly life-threatening motor disturbances and extra-trigeminal spread. From two to six years elapsed between the first sensory symptoms and the onset of motor disorders. In patients with trigeminal isolated sensory neuropathy (TISN) and in those with FOSMN neurophysiological and histological examination documented a neuronopathy manifesting with trigeminal nerve damage selectively affecting myelinated fibres, but sparing the Ia-fibre-mediated proprioceptive reflex.
  
  
  CONCLUSIONS
  Although no clinical diagnostic criteria can distinguish the two conditions at onset, neurophysiological and nerve-biopsy findings specify that in both disorders trigeminal nerve damage manifests as a dissociated neuronopathy affecting myelinated and sparing unmyelinated fibres, thus suggesting similar pathophysiological mechanisms.
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University, Rome, Italy. giorgio.cruccu@uniroma1.it.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Cruccu
authors.affiliation: Neurology Division, Neurosciences Department, San Filippo Neri Hospital, Rome, Italy. elenapennisi@gmail.com.
authors.forename: Elena M
authors.initials: EM
authors.lastname: Pennisi
authors.affiliation: Department NESMOS, Sant'Andrea Hospital, Rome, Italy. giovanni.antonini@uniroma1.it.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Antonini
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University, Rome, Italy. anbia@inwind.it.
authors.forename: Antonella
authors.initials: A
authors.lastname: Biasiotta
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University, Rome, Italy. distefano.giulia83@gmail.com.
authors.forename: Giulia
authors.initials: G
authors.lastname: di Stefano
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University, Rome, Italy. silvia.lacesa@gmail.com.
authors.forename: Silvia
authors.initials: S
authors.lastname: La Cesa
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University, Rome, Italy. caterinamaria.leone@gmail.com.
authors.forename: Caterina
authors.initials: C
authors.lastname: Leone
authors.affiliation: Cellular Diagnostics Unit, Department of Clinical and Molecular Medicine, Sant'Andrea Hospital, Rome, Italy. salvatore.raffa@uniroma1.it.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Raffa
authors.affiliation: Department of Neurology, University of Würzburg, Würzburg, Germany. sommer@uni-wurzburg.de.
authors.forename: Claudia
authors.initials: C
authors.lastname: Sommer
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University, Rome, Italy. andrea.truini@uniroma1.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Truini
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D018450:Disease Progression; D005157:Facial Pain / Q000503:physiopathology*; D005260:Female; D006801:Humans; D006987:Hypesthesia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D016472:Motor Neuron Disease / Q000503:physiopathology*; D009437:Neuralgia / Q000503:physiopathology*; D011434:Proprioception; D012018:Reflex; D013577:Syndrome; D014276:Trigeminal Nerve / Q000473:pathology*; D020433:Trigeminal Nerve Diseases / Q000473:pathology / Q000503:physiopathology*; D055815:Young Adult