Pain laterality in relation to site of pain and diagnosis

A lateralized model of the pain-depression dyad

Chronic pain and depression are two frequently co-occurring and debilitating conditions. Even though the former is treated as a physical affliction, and the latter as a mental illness, both disorders closely share neural substrates. Here, we review the association of pain with depression, especially when symptoms are lateralized on either side of the body. We also explore the overlapping regions in the forebrain implicated in these conditions. Finally, we synthesize these findings into a model, which addresses gaps in our understanding of comorbid pain and depression. Our lateralized pain-depression dyad model suggests that individuals diagnosed with depression should be closely monitored for pain symptoms in the left hemibody. Conversely, for patients in pain, with the exception of acute pain with a known source, referrals in today's pain centers for psychological evaluation should be part of standard practice, within the framework of an interdisciplinary approach to pain treatment.

Altered structure and functional connection in patients with classical trigeminal neuralgia

Classical trigeminal neuralgia (TN) is a specific type of neuropathic orofacial pain of which the plasticity of brain structure and connectivity have remained largely unknown. A total of 62 TN patients were included and referred to MRI scans. Voxel-based morphometry was used to analyze the change of gray matter volume. Resting-state functional imaging was used to analyze the connectivity between brain regions. The results showed gray matter volume reduction in components of the prefrontal cortex, precentral gyrus, cerebellar tonsil, thalamus, hypothalamus, and nucleus accumbens among right TN patient and in the inferior frontal gyrus, precentral gyrus, cerebellum, thalamus, ventral striatum, and putamen among left TN patients. The connections between the right superior frontal gyrus and right middle frontal gyrus were lower in right TN patients. The connection between the left precentral gyrus and the left superior frontal gyrus was lower while the connection between bilateral thalamus was higher in left TN patients. The changes of volume in bilateral thalamus of right TN patients and left ventral striatum of left TN patients, and the connectivity between bilateral thalamus of left TN patients were moderately correlated with pain duration. These findings suggest that brain regions such as the thalamus may not only be involved in processing of pain stimuli but also be important for the development of TN. The left hemisphere may be dominant in processing and modulation of TN pain signal. Chronification of TN induces volume changes in brain regions which are associated with emotional or cognitive modulation of pain. Hum Brain Mapp 39:609-621, 2018. © 2017 Wiley Periodicals, Inc.

[Lateral asymmetry of the human pain sensitivity.]

In repeated clinical studies a preponderance of pain syndromes on the left side of the body has frequently been observed. Experimental studies in humans revealed a lower pain threshold on the left, nondominant side. On the other hand, some studies do not confirm this lateralization. Since pain threshold is not a very valid measure of pain sensitivity in the range beyond threshold, and since clinical studies are limited by simply counting the incidence of the pain syndromes, we investigated whether a significant lateralization of pain sensitivity exists in the entire range beyond pain threshold. Handedness and gender were included as factors. For experimental pain stimulation in 24 subjects three different methods were used: local pressure on the middle phalanxes, a modified submaximal effort tourniquet test, and submerging the hands into cold water. For pain measurement beyond threshold we used the category splitting procedure (Heller).All three methods of stimulation produced corresponding results. Lefthanded subjects showed decreased pain sensitivity on the left side, right-handed subjects on the right side. This was true for the total range of pain sensitivity. For pain induced by pressure, lateral asymmetry increased with pain intensity, for the other two methods it was constant. Lateral asymmetry was found in all subjects, but significant differences could only be demonstrated in female Ss. It is concluded that both gender and handedness contribute to lateral asymmetry of pain sensitivity in man.

Pain drawings and concepts of pain among patients with "half-body" complaints

OBJECTIVE

To explore main features of pain drawings and concepts about illness in patients seeking help for "half-body" complaints at two primary health care centres in different parts of Sweden.

METHODS

A qualitative study of pain-drawings and tape-recorded semi-structured interviews analysed by qualitative methods in 20 patients (4 men, 16 women, aged 37-68 years) from five health centers. Three of them were native Swedes and 17 were foreign-born.

RESULTS

All complained of pain in a left (three-fourth) or right (one-fourth) body-half, mainly in front. Some had general pain with a "worse side". Many said they had pain only on the "edges" and outlined the margins on the side of pain, but excluded the "face". Posterior drawings often received a line in the middle dividing the body in lateral halves. Pain was referred to as a "growing" thing - ("It") - that could spread ("jump") to the other side, grow and eventually paralyse them. "It" was believed as caused by body imbalance, natural factors or supernatural forces.

CONCLUSION

"Half-body" pain was an expression that in main was used by middle-aged patients to denote an initially superficial and frontal one-sided pain that could spread and become dangerous to their health.

PRACTICE IMPLICATIONS

Patients with half-body complaints should be taken seriously and met with respect by doctors and other health care personnel, particularly in cross-cultural consultations.

[Brain tumor and headache.]

METHODS

The possible association of brain tumour with headache was investigated in 100 patients seen for brain surgery. Preoperatively, 43 patients suffered from headache. These patients were thoroughly questioned about the nature of their pain. Investigation included the McGill Pain Questionnaire.

RESULTS

In only 11 of the patients was headache the primary symptom of a brain tumour. Pain intensity was found to be lower in patients with brain tumour then in those with extracranial tumours or headache of other origins. Female subjects, patients under 50 years of age and those with elevated intracranial pressure experienced more intensive pain. Diurnal variation in pain intensity was observed in 60% of patients with headache. There was no evidence, however, of an association with elevated intracranial pressure.

CONCLUSIONS

Our investigations yielded new information concerning the epidemology of headache accompanying brain tumours. Headache is not an early cardinal symptom of brain tumours, as was generally believed earlier. With the help of the McGill Pain Questionnaire a fine quantitative and qualitative characterization of headache of different origins could be made. The connection between tumour localization and pain lateralization, as well as the possible mechanisms of intracranial pain projection was extensively analysed. The interpretations of the results are at best hypotheses and they do not help determine why more than half of the patients with brain tumour did not experience headache.

Laterality and modality-specific effects of chronic pain

Previous investigations indicated that thresholds to nonpainful tactile stimuli were elevated in chronic-pain patients when compared with pain-free individuals (Seltzer & Seltzer, 1986; Seltzer et al., 1988). The present study attempted to determine whether thresholds to tactual and visual stimuli also were elevated by chronic pain. Furthermore, lateralization of the pain effect on tactile thresholds was assessed by obtaining thresholds from both left and right arms. A decrease in tactile sensitivity to nonpainful stimuli in chronic-pain patients was confirmed, but laterality of the effect was not demonstrated. Visual thresholds were not significantly affected by chronic pain. The data in the present study, taken together with other data, support the proposition that pain does not affect right hemispheric processes more than left hemispheric processes.

Somatosensory findings in postherpetic neuralgia

Somatic sensory perception thresholds (warm, cold, hot pain, touch, pinprick, vibration, two-point discrimination), allodynia and skin temperature were assessed in the affected area of 42 patients with unilateral postherpetic neuralgia (PHN) and 20 patients who had had unilateral shingles not followed by PHN (NoPHN), and in the mirror-image area on the other side. There was no difference between the two groups for age or length of time after the acute herpes zoster infection. The PHN group showed significant changes in all sensory threshold measurements when the affected area was compared with the mirror-image area on the unaffected side, while the NoPHN group exhibited no threshold changes. Mechanical allodynia was present in 87% of the PHN group; half of the 12 patients with ophthalmic PHN showed extension of allodynia to the maxillary distribution. No differences in skin temperature were recorded between affected and unaffected regions in either group. Our findings show a deficit of sensory functions mediated by both large and small primary afferent fibres and also suggest major central involvement in the pathophysiology of the condition. If PHN does not occur following acute herpes zoster, recovery of neural functions appears to be good.

Pain and its absence in an unfortunate family of amputees

A family is described in which 5 male members sustained major traumatic injuries of their limbs. Two of these men had amputations of two of their limbs. The one surviving amputee is left handed. The development of phantom sensations, phantom pain and stump pain was unpredictable, despite their being first-degree relatives, and was independent of handedness.