Investigators planned to adopt the N-of-1 trial approach to objectively test the effectiveness of ultra-micronized PEA at an individual level in our older outpatients. 65 years old or older persons referring to the Geriatric Unit of the Fondazione IRCSS Ca' Granda Ospedale Maggiore Policlinico of Milan complaining of noncancer chronic pain of any origin will be eligible. Each trial will be a placebo-controlled randomized crossover trial including two um-PEA (600 mg twice a day) and placebo treatment pairs. Investigators will secondarily meta-analyse the performed N-of-1 trials to obtain an estimate of the average effect of um-PEA compared with placebo using a frequentist and Bayesian approach.

Background: Chronic pain in the elderly is highly prevalent, often underestimated, and associated with adverse outcomes. Most available analgesic drugs are often either ineffective or not tolerated, and burdened with many side effects. Palmitoylethanolamide (PEA) is an endogenous widely distributed N-acylethanolamina involved in neuroinflammation and pain generating processes. Formulations containing ultra-micronized Palmitoylethanolamide (um-PEA) are available on the market but their effectiveness on chronic pain in highly heterogeneous geriatric patients is not clear and likely not generalizable. Investigators planned to adopt the N-of-1 trial approach to objectively test the effectiveness of ultra-micronized PEA at an individual level in our older outpatients.

Methods/Design: 65 years old or older persons referring to the Geriatric Unit of the Fondazione IRCSS Ca' Granda Ospedale Maggiore Policlinico of Milan complaining of noncancer chronic pain of any origin will be eligible. Each trial will be a placebo-controlled randomized crossover trial including two um-PEA (600 mg twice a day) and placebo treatment pairs. um-PEA or placebo 3-week periods will be separated by 2-week washout intervals to overcome the possible carryover effect. Pain intensity, need for on-demand analgesic medications, and impact on daily activities will be evaluated. Also, cognitively impaired patients will be eligible as long as the expression of pain can be recognized and its frequency assessed by a caregiver. Trial results will be then discussed with the patient/caregiver and the treating physician to decide whether to continue the treatment. The impact of the N-of-1 approach on the physician's management plan and confidence will be assessed. Investigators will secondarily meta-analyse the performed N-of-1 trials to obtain an estimate of the average effect of um-PEA compared with placebo using a frequentist and Bayesian approach.

Discussion: While pursuing an ultimate clinical objective, i.e. to empirically and objectively decide the best treatment choice for an individual older patient with chronic pain, these series of geriatric N-of-1 trials on PEA will bring the Evidence Based Medicine principles into the care of patients not usually represented in conventional randomized controlled trials, and realize a patient-centered outcome approach necessary to improve appropriate prescribing in elderly patients with multimorbidity and polypharmacy.

Inclusion Criteria:

• Pain is located at the back (any level) and/or at the joints and/or at the limbs.
• The pain is chronic, i.e. it has been present for at least 6 months, even if with fluctuations.
• The pain is attributable to one or more of the following conditions: osteoarthritis/osteoarthrosis; spondylosis; radiculopathy; diabetic peripheral neuropathy; post-herpetic neuralgia; chronic idiopathic axonal polyneuropathy; fibromyalgia; or pain of uncertain origin or idiopathic, as long as it has had and it is expected to have a chronic nature, even if with spontaneous fluctuations.

Exclusion Criteria:

• cancer-related pain
• clear ischemic pathogenesis for pain (e.g. claudicatio intermittens or critical limb ischemia)