Monoclonal antibodies (mABs) targeting calcitonin gene-related peptide (CGRP) proved effective in the preventive treatment of episodic and chronic migraine as well as in difficult-to-treat patients such as those who had previously failed multiple prevention treatments or those with associated medication overuse (MO).

A characteristic dysfunction in Chronic Migraine (CM) is sensitization, occurring peripherally in the trigeminovascular system but then spreading to the central nervous system, where it manifests with an increased neuronal excitability in multiple areas. Several neurophysiological studies in CM patients have demonstrated the occurrence of central sensitization in the brain as well as at the spinal level.

MicroRNAs (miRNAs) are involved in the generation and maintenance of chronic pain. Current evidence suggests that specific miRNAs may also play a role in migraine, thus representing possible biomarkers of the disease. A previous study reported an upregulation of miR-34a-5p and miR-382-5p, implicated in the regulation of GABAergic signaling and IL-10 gene expression respectively, during migraine attacks.

The aim of this open label, hypothesis generating study is the evaluation of the impact of erenumab treatment on neurophysiological, biomolecular and psychological aspects in a representative cohort of CM patients who had previously failed at least 2 preventive treatments.

This study consisted of a first screening visit with a Neurologist of the Headache Science Centre of the IRCCS Mondino Foundation, during which a full neurological and general examination was performed, and the data collected on the routine headache diary used by all patients attending Mondino Foundation was checked to confirm inclusion/exclusion criteria.

If a patient fulfilled criteria, he/she was enrolled in a baseline observation period for a month. At the end of the baseline observation period (T0), if inclusion/exclusion criteria were still satisfied, patients completed the following procedures: recording of clinical and demographical features, vital signs evaluation, neurophysiological assessment and psycological interview based on DSM (The Diagnostic and Statical Manual of Mental Disorders), venous blood sampling, and compilation of a set of self-administered questionnaires about psychological state, health status and quality of life.

At T0, the patients were treated with the first dose of erenumab 70 mg subcutaneously.

After 28 days (4 full weeks), patients returned for the second visit (T1) to report clinical variables and adverse events. During T1, the second injection of erenumab 70 mg was administered, while a third and last dose of erenumab 70 mg was self-administered at home by the patients themselves after an additional 28-day interval (T2). The last visit of the study (T3) was then planned 56 days from T1, that was 28 days after the last dose of erenumab. At T3, the patients were tested with the same multi-disciplinary evaluation performed at T0: recording of clinical and demographical features, vital signs evaluation, neurophysiological assessment, venous blood sampling, and compilation of questionnaires concerning patients' psychological state, health status and quality of life.

Nociceptive withdrawal reflex measurements. The nociceptive withdrawal reflex (NWR) is considered an objective and solid neurophysiological technique for the study of spinal nociceptive transmission. The reflex was recorded in the lower limb according to a well validated procedure, in a quiet environment by an expert technician between 09:00 AM and 11:00 AM. Patients were in a comfortable position with their ankle flexed at 90° and knee flexed at 130°. The sural nerve was stimulated electrically behind the lateral malleolus with a pair of Ag/AgCl surface electrodes. The electrical stimulation was made of 5 consecutive squared pulses (1 ms, 200 Hz), randomly delivered every 60-120 seconds. The electromyographic sweep (Synergy, Medelec, United Kingdom) was recorded from the capitis brevis of the homolateral biceps femoris with a pair of Ag/AgCl surface electrodes. A staircase method was used for all the threshold evaluations, and the intensity was increased by 0.3 mA per step. The recording parameters were: analysis time 300 ms, sensitivity 20 mV, and filter bandpass 3 to 3000 Hz.

The investigators first evaluated the single stimulus reflex threshold of the NWR (RTh), defined as the lowest intensity (mA) able to induce 3 consecutive stable muscular responses of at least 20 mV and 10 ms. They also evaluated the average AUC (Area Under the Curve - mV x ms), the average latency (ms), and the subjective pain perception rated on a 0-10 points visual analogue scale (VAS-RTh).

Then the investigators evaluated the temporal summation threshold (TST), by means of a train of 5 electrical stimuli at a frequency of 2 Hz. TST was defined as the lowest intensity (mA) able to elicit 3 consecutive stable muscular responses of at least 20 mV and 10 ms in the fourth and fifth electromyographic sweeps. They also evaluated the subjective pain perception of the first (VAS-TST-1) and fifth (VAS-TST-5) stimulus of the TST on a 0-10 points visual analogue scale.

MicroRNAs expression. The microRNA expression was evaluated by real-time reverse transcription (RT) PCR in peripheral blood mononuclear cell (PBMCs).

PBMCs isolation: blood samples (10 ml) was collected within ethylenediamine tetra-acetic acid containing tube from participants. The blood samples were diluted in 1:1 ratio with phosphate buffer saline (PBS) (Sigma). Diluted blood samples were slowly loaded into Ficoll separating solution (10 ml) (Sigma) and centrifuged at 800 g for 30 min at room temperature. PBMCs accumulated as the middle white monolayer, were washed twice in sterile PBS at 300 g for 15 min. After washing, PBMCs were pelleted and stored at -80° C until use.

MicroRNAs gene expression: isolation of RNA from PBMCs was carried out using the Direct-zol RNA Mini prep plus (Zymo Research). RNA concentration was determined by absorbance at 230 and 280 nm using the NanoDrop Spectrophotometer (Nanodrop™ Thermo Fisher Scientific, Euroclone Milano). Synthesis of cDNA was performed by using MirXMirna First strand Synthesis (Takara-Diatech, Jesi-An Italy) and TB Green q-Rt PCR is used (Takara-Diatech, Jesi-An Italy) to determine expression levels of miRNA-34a-5p and miRNA-382-5p. The denaturation was performed at 95°C and the amplification was performed through two-step cycling (95-60°C) for 40 cycles with a Light Cycler 480 Instrument RT-PCR Detection System (Roche, Milan, Italy). Target gene expression levels was normalized with U6 (a type of small nuclear RNA), used as housekeeping gene. Gene expression levels were calculated according to 2-∆Ct = 2 - (Ct gene - Ct housekeeping gene) formula by using Ct values.

Disability and psychological evaluations.

The battery included evaluations for:

4) Migraine-related disability and associated features:

• the Migraine Disability Assessment (MIDAS) test: 0-5 (grade I): minimal disability, 6-10 (grade II): mild disability, 11-20 (grade III): moderate disability, 21-40 (grade IVa): severe disability, 41 and higher (grade IVb): very severe disability;

• the Headache Impact Test-6 (HIT-6): 49 or less: no impact, 50-55: some impact, 56-59: substantial impact, 60-78 severe impact;

• Nociceptive Rating Scale for the assessment of average intensity of migraine pain: 0 no pain - 10 very severe;

• Allodynia Symptom Checklist (ASC-12): 0-3: mild cutaneous allodynia, 6-8: moderate cutaneous allodynia, 9 and higher: severe cutaneous allodynia.

  5) Quality of life:

• the Migraine-Specific Quality-of-Life Questionnaire (MSQ): 14-item assessment, with each item rated on a 6-point scale (ranging from "none of the time" to "all of the time"). Raw scores are then transformed to a 100-point scale, with higher scores indicating better quality of life;

• Short Form Health Survey (SF-36): 11-item assessment referring to two main sub-domains, namely the Mental Component Summary (MCS), and the Physical Component Summary (PCS);

• HEALTH 0-100: patients were asked to score on a scale range of 0-100 their general health status at the precise moment of evaluation.

  6) Psychological State:

• Hospital Anxiety and Depression Scale (HADS): a 14-items questionnaire on a 4-point (0-3) Likert scale assessing symptoms of anxiety and depression. A score of 8 or higher in the two different domains is considered significant for anxiety and/or depression;

• Leeds Dependence Questionnaire (LDQ): a 10-item instrument on 0-3 scale to measure dependence upon a variety of substances. No cut-off score indicative of dependence has been established;

• Toronto Alexithymia Scale (TAS-20): a 20-item questionnaire on a 5-point (1-5) Likert scale assessing alexithymia traits, i.e., individuals' difficulty in expressing their own feelings in words. A score of 61 or higher was considered significant for the presence of alexithymia;

• Childhood trauma questionnaire: including 13 items referring to different types of childhood traumas that were considered in term of total number of traumatic experiences;

• Stressful life-events questionnaire: consisting in a list of 58 stressful life events (e.g., moving, divorce, new work, dismissal, etc.). Patients were requested to tick those events that had occurred to them in the last 10 years.

Inclusion Criteria:

• age 18 to 65 years
• history of CM or CM+MO for at least 12 months prior to enrollment [10]
• previous failure of at least two different pharmacological classes of preventive therapies

Exclusion Criteria:

• other neurologic or neuropsychiatric diseases
• other chronic painful syndromes
• other types of primary or secondary headaches
• use of more than one preventive medication at baseline
• previous reported adverse reaction to latex
• pregnancy or lactation

Forty patients, affected by CM or CM+MO according to the International Classification of Headache Disorders (ICHD) -3 criteria were enrolled.