The analgesic treatment will be tailored to the patient's medication and will be based on 3 levels (based on Ventafridda et al., 1985):

• Level 1 : Non-opioid analgesics
• Level 2 : Weak opioids analgesics
• Level 3 : Strong opioids analgesics

If the patient is already on pain medications, we will add the lowest effective dose of the level above the level of the regular pain medications of the patient. (e.g. if the patient has no analgesic treatment, he will be given a non-opioid analgesic (level 1). If he already has a level 1 treatment, we will go for level 2 medication. If he has level 2 treatment, we will go for level 3. And if the patient is already at level 3, we will increase the dosage by steps (reference: 5mg oxycodone as first choice for level 3 drugs)). Preferably, the medication will be administered by oral intake or gastrostomy feeding tube. If it is not possible, other routes of administration are allowed.

Folavit capsules will be used as a placebo

• Level 1 : Paracétamol 1g/Acetaminophène 1g, Ibuprofène 600mg, Diclofénac 50mg.

• Level 2: Tramadol 50mg.

• Level 3: Oxycodone 5mg, Morphine sulfate 10mg.

• Increase of a prior level 3 medication :

  1. 1/6 of the total dose of daily level 3 medication (e.g. the patient receives 30mg of oxycodone a day. He will be administered a single dose of 5 mg for the study), defined as a breakthrough dose in the management of chronic pain. To standardize the treatment, the dose of the prior level 3 medication will be converted to oxycodone. Several online tools exist to do the conversion between opioids (e.g. mobile app Orthodose ®).
  2. If the oral intake or the gastrostomy use is not possible, the breakthrough dose will be administered by subcutaneous route. The dose will also be 1/6 of the daily dose and will be converted to injectable morphine. Conversion to injectable morphine will be performed with any equivalence tool (such as the mobile app Orthodose ®)

The NCS-R (Chatelle et al., 2012) is used to assess the perception of acute pain in patients with disorders of consciousness. It is composed of 3 subscales (motor, verbal and facial expressions) respectively scoring from 0 (no response) to 3 (highest response level). Here the NCS-R is administered in 4 different conditions: at rest, during tactile stimulation, during experimental nociceptive stimulation (pressure on the bed of the left and right nail) and during mobilization (physiotherapy).

The CRS-R (Giacino et al., 2004) is the gold standard for the behavioural assessment of the level of consciousness and is widely used in patients with chronic disorders of consciousness. The CRS-R is composed of six subscales that assess the following domains: visual, motor, auditory and oro-motor/verbal functions, as well as communication, and arousal. The score ranges from 0 to 23, in which the lowest score indicates coma and the highest score indicates the emergence from the minimally conscious state. The diagnosis is made according to the presence\absence of particular behavioural responses.

The MAS (Bohannon et al., 1987) is used to assess spasticity (reflex contraction in response to passive stretching). This is a scoring scale from 0 (no increase in muscle tone) to 4 (very strong increase in tone, stiffness), which will depend on the speed of execution of the movement (the faster the limb will be mobilized the more spastic it will be) and which must be performed at least 3 times for each joint.