Cortical excitability in episodic cluster headache

Background: Cluster headache (CH) is a severe primary headache
disorder, whose pathophysiological processes remain largely unknown.
Along with central disinhibition of the trigeminal nociceptive system and
hypothalamic impairment, a cortical involvement has been supposed.
Aim: To evaluate cortical excitability in episodic CH patients by using
different paradigms of transcranial magnetic stimulation (TMS).
Methods: Twenty-five patients with episodic CH and thirteen healthy
subjects underwent an experimental session where we evaluated, in both
hemispheres, motor-cortical response to: 1) single-pulse TMS: i.e. motor
threshold (MT); input-output (IO) curves and cortical silent period (CSP) and
2) paired-pulse TMS: i.e. intracortical facilitation (ICF) and short intracortical
inhibition (SICI). Thirteen patients were evaluated outside bout, while the
remaining twelve patients were inside bout at the time of recording.
Results: We showed increased ICF values in the hemisphere ipsilateral to
the side of pain in patients evaluated both outside and inside bout.
Differently, IO curves showed increased slope in both hemispheres in
patients examined outside bout, but only in the hemisphere contralateral
to the affected side in those evaluated during bout.
Conclusions: Our results show a condition of increased cortical excitability
in episodic CH both outside and inside bout. Interestingly, cortical
excitability was greater in the hemisphere ipsilateral to the side of pain in
patients outside bout, but decreased in patients inside bout possibly due to
activation of compensatory inhibitory mechanisms of cortical excitability.
Along with subcortical and peripheral mechanisms, changes in cortical
excitability could also play an important role in the pathophysiology of CH.
No conflict of interest.