Altered central somatosensory processing in chronic pain patients with "hysterical" anesthesia.
OBJECTIVE
The authors hypothesized that central factors may underlie sensory deficits in patients with nondermatomal somatosensory deficits (NDSD) and that functional brain imaging would reveal altered responses in supraspinal nuclei.


BACKGROUND
Patients with chronic pain frequently present with NDSD, ranging from hypoesthesia to complete anesthesia in the absence of substantial pathology and often in association with motor weakness and occasional paralysis. Patients with pain and such pseudoneurologic symptoms can be classified as having both a pain disorder and a conversion disorder (Diagnostic and Statistical Manual of Mental Disorders-IV classification).


METHODS
The authors tested their hypothesis with functional MRI (fMRI) of brush and noxious stimulation-evoked brain responses in four patients with chronic pain and NDSD.


RESULTS
The fMRI findings revealed altered somatosensory-evoked responses in specific forebrain areas. Unperceived stimuli failed to activate areas that were activated with perceived touch and pain: notably, the thalamus, posterior region of the anterior cingulate cortex (ACC), and Brodmann area 44/45. Furthermore, unperceived stimuli were associated with deactivations in primary and secondary somatosensory cortex (S1, S2), posterior parietal cortex, and prefrontal cortex. Finally, unperceived (but not perceived) stimuli activated the rostral ACC.


CONCLUSIONS
Diminished perception of innocuous and noxious stimuli is associated with altered activity in many parts of the somatosensory pathway or other supraspinal areas. The cortical findings indicate a neurobiological component for at least part of the symptoms in patients presenting with nondermatomal somatosensory deficits.
Comprehensive Pain Program, Toronto Western Hospital, Ontario, Canada.
A
A
Mailis-Gagnon
I
I
Giannoylis
J
J
Downar
C L
CL
Kwan
D J
DJ
Mikulis
A P
AP
Crawley
K
K
Nicholson
K D
KD
Davis
D000328:Adult; D000654:Amobarbital; D001931:Brain Mapping; D003291:Conversion Disorder / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006179:Gyrus Cinguli / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D006987:Hypesthesia / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008881:Migraine Disorders / Q000523:psychology; D008959:Models, Neurological; D008960:Models, Psychological; D010147:Pain Measurement; D010148:Intractable Pain / Q000150:complications / Q000523:psychology; D010465:Perception / Q000502:physiology; D016548:Prosencephalon / Q000473:pathology / Q000503:physiopathology*; D013003:Somatosensory Cortex / Q000473:pathology / Q000503:physiopathology*; D013788:Thalamus / Q000473:pathology / Q000503:physiopathology; D014110:Touch; D014947:Wounds and Injuries / Q000523:psychology
D000654:Amobarbital