Yair Sharav

Idiopathic trigeminal neuralgia: sensory features and pain mechanisms

&NA; We present a case report of a patient with the typical sensory features of idiopathic trigeminal neuralgia (ITN). The pain was elicited by innocuous stimuli, summated with repeated stimulation, radiated outside the stimulus zone, referred to a distant site, persisted beyond the period of stimulation, and exhibited a variable refractory period. Unusual sensory features included multiple trigger zones that changed over time and involved all 3 trigeminal divisions. Our sensory evaluation indicated that the pain was evoked by repetitive activation of rapidly adapting, A&bgr;, low‐threshold mechanoreceptive afferents. However, activation of such mechanoreceptive afferents alone never produces pain in normal situations and often leads to a suppression of pain responsivity. The findings support the idea that the mechanism of pain in ITN involves pathophysiological mechanisms in the central nervous system. Our hypothesis is that structural and functional changes in the trigeminal system result in an alteration in the receptive field organization of wide‐dynamic‐range (WDR) neurons. There appears to be an alteration in the surround inhibition mechanism of these neurons leading to an expansion of their touch receptive fields. This results in touch stimuli producing activity in WDR neurons that mimics the activity produced under normal conditions by noxious stimuli. Since WDR neurons participate in the encoding of the perceived intensity of noxious stimuli, a series of punctate tactile stimuli are now perceived as localized, pin‐prick or electric shock‐like sensations. Similar pathophysiological mechanisms may explain, in part, the pain of peripheral neuropathies associated with postherpetic neuralgia, diabetes and causalgia.

Trigeminal neuralgia with lacrimation or SUNCT syndrome

An intimate relationship between trigeminal neuralgia (TN) and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) syndrome, based on similar clinical signs and symptoms and on cases demonstrating possible “transformation” from one entity to the other, has been widely accepted. We evaluated the presence of lacrimation in 22 consecutive cases that had been diagnosed as TN. Ipsilateral lacrimation was reported by 6 such cases (5M, 1F). These cases responded to antineuralgic therapy with concomitant resolution of lacrimation and were clinically very similar to TN. The differential diagnosis and the possibility of lacrimation in TN are discussed.

Autotomy behavior in rats following peripheral deafferentation is suppressed by daily injections of amitriptyline, diazepam and saline

&NA; Amitriptyline, a tricyclic antidepressant (TCA), was effective in suppressing self‐mutilation of a peripherally deafferented hind paw in rats (‘autotomy’). This effect was not due to the drugs sedative effect, since locomotor activity was not lower in treated than untreated rats. Daily injections of normal saline also suppressed autotomy, but for a shorter period of time than amitriptyline. This effect was not apparent in diazepam‐treated rats, suggesting that the saline injection delayed autotomy as a result of stress‐induced anti‐nociception. Since amitriptyline is effective in humans in alleviating certain chronic pain disorders, these results further corroborate the suggestion that autotomy is a model of chronic pain, sensitive to centrally acting analgesics and to some forms of stress.

The International Classification of Headache Disorders: accurate diagnosis of orofacial pain?

The aim was to apply diagnostic criteria, as published by the International Headache Society (IHS), to the diagnosis of orofacial pain. A total of 328 consecutive patients with orofacial pain were collected over a period of 2 years. The orofacial pain clinic routinely employs criteria published by the IHS, the American Academy of Orofacial Pain (AAOP) and the Research Diagnostic Criteria for Temporomandibular Disorders (RDCTMD). Employing IHS criteria, 184 patients were successfully diagnosed (56%), including 34 with persistent idiopathic facial pain. In the remaining 144 we applied AAOP/RDCTMD criteria and diagnosed 120 as masticatory myofascial pain (MMP) resulting in a diagnostic efficiency of 92.7% (304/328) when applying the three classifications (IHS, AAOP, RDCTMD). Employing further published criteria, 23 patients were diagnosed as neurovascular orofacial pain (NVOP, facial migraine) and one as a neuropathy secondary to connective tissue disease. All the patients were therefore allocated to predefined diagnoses. MMP is clearly defined by AAOP and the RDCTMD. However, NVOP is not defined by any of the above classification systems. The features of MMP and NVOP are presented and analysed with calculations for positive (PPV) and negative predictive values (NPV). In MMP the combination of facial pain aggravated by jaw movement, and the presence of three or more tender muscles resulted in a PPV = 0.82 and a NPV = 0.86. For NVOP the combination of facial pain, throbbing quality, autonomic and/or systemic features and attack duration of > 60 min gave a PPV = 0.71 and a NPV = 0.95. Expansion of the IHS system is needed so as to integrate more orofacial pain syndromes.

Chronic Orofacial Pain

Chronic orofacial pain (COFP) is an umbrella term used to describe painful regional syndromes with a chronic, unremitting pattern. This is a convenience term, similar to chronic daily headaches, but is of clinically questionable significance: syndromes that make up COFP require individually tailored diagnostic approaches and treatment. Herein we describe the three main categories of COFP: musculoskeletal, neurovascular, and neuropathic. For many years, COFP and headache have been looked upon as discrete entities. However, we propose the concept that because COFP and headaches share underlying pathophysiological mechanisms, clinical characteristics, and neurovascular anatomy, they should be classified together.

Diagnosis and treatment of persistent pain after trauma to the head and neck

PURPOSE A retrospective and prospective study on 22 cases of persistent pain after trauma to the head and neck is presented. According to the predominant symptoms and signs, pain patterns could be divided into musculoskeletal, vascular, and neuropathic, facilitating treatment decisions. Most cases were musculoskeletal in origin, with many demonstrating a combination of two or three pain states. RESULTS The variety of pain complaints and their underlying pathophysiology are discussed and treatments for specific pain states are examined. CONCLUSION Amitriptyline was the most useful drug in that it provided pain relief in musculoskeletal, vascular, and some neuropathic pain conditions. Multidrug therapy may be indicated in some recalcitrant cases, and drug alternatives are discussed.

Orofacial pain with vascular-type features

OBJECTIVE To examine whether a classifiable primary vascular-type craniofacial pain subgroup exists that predominantly affects intraoral structures. STUDY DESIGN Fifty-five patients were chosen prospectively according to the following inclusion criteria; periodic craniofacial pain that was unilateral, pulsatile, severe, and that may wake the patient from sleep. Accompanying phenomena could include local autonomic and/or systemic signs. Twenty-six cases could be further classified into one of the categories of vascular craniofacial pain. The remaining 29, all with predominantly intraoral pain, were not readily classifiable. RESULTS Of the 29 patients 70% were women, with an average onset-age of 42.6 years. All reported severe, episodic pain that was usually unilateral and lasted minutes to hours. In all, 55% of patients had autonomic or systemic signs, 48% had pulsatile pain, and 35.4% of patients were awakened by the pain. CONCLUSION Although clinical similarities were observed within these patients, further studies are needed to confirm vascular orofacial pain as a clear diagnostic category.

SUNCT syndrome: Case report and literature review

The case of a woman with short neuralgiform paroxysmal pain of 2 years duration is described. Pain attacks were always accompanied by ipsilateral lacrimation and conjunctival injection. Standard anti-neuralgic therapy, amitriptyline and indomethacin, failed to eliminate or reduce pain. At the end of a 30-month active period the patient seemed to have gone into remission. We believe this to be a case of short-lasting, unilateral, neuralgiform headache attacks with conjunctival injection and tearing (SUNCT), the first reported in the dental literature and the 24th in the general medical literature. The differential diagnosis of the case and relevant literature are discussed.

Modulation of the jaw-opening reflex by peripheral electrical stimulation

Abstract Modulation of the jaw-opening reflex (JOR) by peripheral electrical stimulation was studied in the rat. The JOR was evoked by electrical stimuli delivered to the tongue, infraorbital nerve, or tooth pulp chamber, and single-pulse conditioning stimuli were delivered to the forelimb, hind limb, or tail. Threshold current for eliciting the JOR was modulated in a biphasic manner with facilitation when the delay between conditioning and test stimuli was short (peaking at 10 to 15 ms) and inhibition at longer intervals (peaking at 40 to 60 ms). Modulation was similar for all peripheral conditioning sites and was not affected by Fentanyl, naloxone, or picrotoxin. Thus, the modulation of the JOR by single-pulse peripheral electrical stimulation is a widespread, nonsegmental phenomenon, and is probably not associated with the endogenous opiate system. Data collected during the course of this study call into question the usefulness of the JOR elicited by electrical stimulation in the rat incisor tooth pulp chamber as a pain model.

The spatial distribution, intensity and unpleasantness of acute dental pain

&NA; The distribution, intensity and unpleasantness of acute dental pain were studied in 196 patients. Dental pain was classified by source according to 7 anatomical sites: dentinal, pulpal, pulpal and periapical, periapical, pericoronal, papular and periodontal. The distribution of dental pain was classified by the frequency of pain spread throughout the sample, by the extent of pain spread for a particular pain source, that is, the number of vectors of spread and by the pain reference locations in the face and head. Pain‐intensity and pain‐unpleasantness were assessed on Visual Analogue Scales. The frequency and extent of pain spread varied as a function of source. However, specific patterns of pain spread were not associated with particular pain sources. There was considerable overlap in patterns of spread between maxillary and mandibular pain sources. The frequency and extent of pain spread was correlated positively with both pain intensity and pain unpleasantness. The correlation between pain ratings and pain spread may be attributed to central mechanisms and interactions between trigeminothalamic neurons. Spatial overlap of pain from maxillary and mandibular pain sources may be due to the large receptive fields of wide dynamic range neurons, that can extend beyond one trigeminal division. These observations indicate that the spatial distribution of acute dental pain is not sufficient as a diagnostic tool for indentifying pain source.