Although many patients with multiple sclerosis (MS) complain of trigeminal neuralgia (TN), its cause and mechanisms are still debatable. In a multicentre controlled study, we collected 130 patients with MS: 50 patients with TN, 30 patients with trigeminal sensory disturbances other than TN (ongoing pain, dysaesthesia, or hypoesthesia), and 50 control patients. All patients underwent pain assessment, trigeminal reflex testing, and dedicated MRI scans. The MRI scans were imported and normalised into a voxel-based, 3D brainstem model that allows spatial statistical analysis. The onset ages of MS and trigeminal symptoms were significantly older in the TN group. The frequency histogram of onset age for the TN group showed that many patients fell in the age range of classic TN. Most patients in TN and non-TN groups had abnormal trigeminal reflexes. In the TN group, 3D brainstem analysis showed an area of strong probability of lesion (P < 0.0001) centred on the intrapontine trigeminal primary afferents. In the non-TN group, brainstem lesions were more scattered, with the highest probability for lesions (P < 0.001) in a region involving the subnucleus oralis of the spinal trigeminal complex. We conclude that the most likely cause of MS-related TN is a pontine plaque damaging the primary afferents. Nevertheless, in some patients a neurovascular contact may act as a concurring mechanism. The other sensory disturbances, including ongoing pain and dysaesthesia, may arise from damage to the second-order neurons in the spinal trigeminal complex.
aCentro Dolore Neuropatico, Dipartimento Scienze Neurologiche, Università La Sapienza, Roma, Italy
bNeurofisiologia Clinica, Dipartimento Scienze Neurologiche, Università La Sapienza, Roma, Italy
cCentro Sclerosi Multipla, Dipartimento Scienze Neurologiche, Università La Sapienza, Roma, Italy
dNeuroradiologia, Dipartimento Scienze Neurologiche, Università La Sapienza, Roma, Italy
eNeurofisiologia, Ospedale di Colleferro, Italy
fMedicina del Dolore, Ospedale di Cagliari, Italy
gIRCCS San Raffaele, Roma, Italy
*Corresponding author. Present address: Dipartimento Scienze Neurologiche, Università La Sapienza, viale Universita 30, 00185 Roma, Italy. Tel.: +39 06 49694209; fax: +39 06 49914758.
Received October 7, 2008
Received in revised form November 27, 2008
Accepted December 15, 2008.