Low Dose Naltrexone for Treatment of Pain in Patients With Fibromyalgia - Effect Via a Central Mechanism?

The patient indicates using a questionnaire-based numerical rating scale (0 = no pain; 100 = worst imaginable pain) mean values of pain at rest, pain during household activity and pain during personal hygienic procedures in the preceding 24 hrs. The cumulated pain scores are used in the statistical analyses.

The FIQR is a fibromyalgia-specific questionnaire containing three domains: function domain, impact domain and symptom domain. The total score of FIQR is calculated by:

• the function domain sum is divided by 3 (upper limit 30)
• the impact domain sum is unchanged (upper limit 20)
• the symptom domain sum is divided by 2 (upper limit 50) The three resulting processed domain scores are summed to obtain the total score of the FIQR (range 0-100)

Pain-related sleep interference is evaluated with the DSIS (0 =pain does not interfere with sleep, 10 = pain completely interferes with sleep]).

Pressure algometry in pre-specified points:

• right occipital region at insertion of m. subocipitalis
• right m. trapezius at the midpoint of the upper border
• right paraspinal region, 3 cm lateral of the midline at level of mid-scapula
• right second costochondral junction
• right lateral epicondyle
• right knee region, at the medial "fat pad" proximal of the meniscus margin

In addition at following control sites:

• right lower arm, at the dorsal lower third
• right fingernail of first digit
• right third metatarsal bone at midpoint Cut-off point is 400 kPa, rate 10-30 kPa/s

HADS is a 14-item questionnaire used to evaluate the subject's level of anxiety and depression; the subjects can rate between 0-21 with a score of eleven as the cutoff point for anxiety or depression

The PCS is a 13-item self-report scale to measure pain catastrophizing: each item is rated on a 5-point nominal scale (0 = not at all, 4 = all the time). It is constructed with three subscales being magnification, rumination, and helplessness.

Self-reported adverse effects related to the treatment:

CNS: irritability, mood changes, drowsiness, lethargy, sleep dysfunction, dizziness cardiovascular system: palpitations, orthostatic hypotension g.i.-system: dyspepsia, nausea, obstipation, diarrhoea urogenital system: urinary retention, urinary incontinence autonomic system: diaphoresis, shivering

Cold pressor test (1min, 10C) - Pressure tolerance threshold before and after Cold Water.

Heat/Capsaicin test - 5min, 45C heat, followed by 30min capsaicin cream 0.075%, Measurement of allodynic (brush, Somedic) and hyperalgesic (Pinprick stimulator 128nm) areas.

Measurement of neuropathic component

BPI-SF allows patients to rate the severity of their pain and the degree to which their pain interferes with common dimensions of feeling and function.

BPI-SF is a widely used Measurement Tool for assessing clinical pain.