Altered Interoceptive Perception and the Effects of Interoceptive Analgesia in Musculoskeletal, Primary, and Neuropathic Chronic Pain Conditions

Abstract

Chronic pain (CP) severely disrupts the daily life of millions. Interoception (i.e., sensing the physiological condition of the body) plays a pivotal role in the aetiology and maintenance of CP. As pain is inherently an interoceptive signal, interoceptive frameworks provide important, but underutilized, approaches to this condition. Here we first investigated three facets of interoceptive perception in CP, compared with pain-free controls. We then introduce a novel interoceptive treatment and demonstrate its capacity to reduce pain severity in CP, potentially providing complementary analgesic treatments. Study 1 measured interoceptive accuracy, confidence and sensibility in patients (N = 60) with primary, secondary musculoskeletal, and neuropathic CP. Compared with matched controls, CP participants exhibited significantly lower interoceptive accuracy and interoceptive confidence. Pain severity was predicted positively by interoceptive accuracy, anxiety and depression, and negatively by interoceptive confidence. Study 2 tested a promising new interoceptive treatment for CP, in a single-blind between-subjects design (N = 51) with primary, secondary musculoskeletal, and neuropathic CP patients. The treatment specifically activates the C-Tactile system, by means of controlled stimulation of interoceptive unmyelinated afferents, at 3 cm/s with a force of 2.5 mN. This treatment led to significant pain reduction (mean 23%) in the CP treatment group after only 11 min, while CP controls who received comparable but non-interoceptive stimulation reported no change in pain intensity. These studies highlight the importance of interoceptive approaches to CP and demonstrate the potential of this novel method of C-Tactile stimulation to provide complementary analgesic treatments.

Keywords: C-Touch; anxiety and depression; chronic pain; interoception; interoceptive treatment.

Figure 1

Interoceptive accuracy (IAcc) alterations in CP. PF: pain-free participants. PP: primary CP participants, SMP: secondary musculoskeletal CP participants, NP: neuropathic CP participants. Mean values: PF µ = 0.61, CI_95% (0.51, 0.71), PP µ = 0.31, CI_95% (0.16, 0.46), SMP µ = 0.44, CI_95% (0.29, 0.59), NP µ = 0.35, CI_95% (0.22, 0.48).

Figure 2

Interoceptive confidence (IAconf) alterations in CP. PF: pain-free participants. PP: primary CP participants, SMP: secondary musculoskeletal CP participants, NP: neuropathic CP participants. Mean values: PF µ = 59.05, CI_95% (51.36, 66.74), PP µ = 31.9, CI_95% (19.22, 44.58), SMP µ = 32.67, CI_95% (18.68, 44.66), NP µ = 36.02, CI_95% (21, 51.04).

Figure 3

Depressive symptoms in CP. PF: pain-free participants. PP: primary CP participants, SMP: secondary musculoskeletal CP participants, NP: neuropathic CP participants. Mean values: PF µ = 7.5, CI_95% (4.29, 10.71), PP µ = 18.83, CI_95% (14.31, 23.35), SMP µ = 17.84, CI_95% (10.77, 24.91), NP µ = 16.11, CI_95% (11.73, 20.49). Red dotted line indicates clinical cut off for depressive symptoms, scores above 14 differentiate mild, moderate and severe depressive states [65,66]).

Figure 4

State anxiety in CP. PF: pain-free participants. PP: primary CP participants, SMP: secondary musculoskeletal CP participants, NP: neuropathic CP participants. Mean values: PF µ = 29.45, CI_95% (26.73, 32.17), PP µ = 41.04, CI_95% (36.92, 45.16), SMP µ = 37.95, CI_95% (30.28, 45.62), NP µ = 41.82, CI_95% (34.53, 49.11). Red dotted line indicates clinical cut off for state anxiety symptoms. Scores above 40 indicate clinical levels of anxiety [67].

Figure 5

Stimulation procedure. (a) Control condition with pressure stimulation at 100 mN (b) experimental condition with optimal C-Tactile stimulation at 3 cm/s and with a force of 2.5 mN.

Figure 6

Interoceptive stimulation reduces Chronic Pain. In the control condition, CP patients (N = 25) received control tactile pressure stimulation at 100 mN. In the experimental condition, CP patients (N = 24) received interoceptive tactile stimulation at 3 cm/s with a force of 2.5 mN. Red dots represent mean values. Control condition, PainPre_NRS µ = 5.52, CI_95% (4.6, 6.44), PainPost_NRS µ = 5.56, CI_95% (4.6, 6.52). Interoceptive stimulation condition, PainPre_NRS µ = 4.25, CI_95% (3.35, 5.15), PainPost_NRS µ = 3.29, CI_95% (2.33, 4.25).