A Contemporary Approach to the Clinical Evaluation of Trigeminal Nerve Injuries

SUMMARY In this article, the authors propose an algorithm for the evaluation of patients with orofacial nerve injury. The algorithm is specifically designed to grade the extent of impairment in sensory capacity and its behavioral impact (for the patient with decreased sensation) and the “complexity” of the pathophysiologic mechanism underlying the pain (for the patient with unpleasant sensation and/or pain). The rationale for this approach is based on limited clinical data that suggest the following. First, different criteria are most appropriately employed to judge whether patients with decreased sensation and with dysesthesia/pain are candidates for definitive surgical treatments.12- 21- 48- 49 Second, patients with decreased sensation appear to benefit from these surgical treatments in proportion to their preoperative impairment in sensory capacity and perceived functional deficits.12,48,49,50 Specifically, factors that support a clinical decision for surgical treatment and are assessed by the algorithm include (1) a patient report of altered sensation that is “bothersome” and affects daily function or behavior,21 (2) physical evidence of self-induced trauma or injury, (3) moderate or severe impairment in sensory capacity,48 and (4) complete anesthesia.12,21,48 In contrast, factors that do not favor the surgical option include (1) a patient report of altered sensation that is rarely noticed and does not affect daily function or behavior, (2) no or little physical evidence of self-induced trauma or injury, and (3) only mild impairment or normal sensory capacity.12,48 Third, patients with dysesthesia/pain fail to benefit from surgical treatments in proportion to the extent that their pain reflects multiple pathologic CNS and autonomic changes.13,29,49 For example, the dysesthetic patient with peripherally mediated allodynia or hyperalgesia has a good prognosis for pain relief, whereas a patient with anesthesia dolorosa is highly unlikely to benefit from nerve exploration/ repair microsurgery. Patients whose primary complaint is pain rather than “numbness” represent a major challenge to the profession because their sensory disorders may be debilitating and re- fractory to surgical treatments. Gregg recently reported that of 84 patients exhibiting chronic posttraumatic orofacial pain, only the hyperalgesic and hyperpathic components of their discomfort were notably reduced by microsurgical treatments.13 Pain was not significantly reduced in patients whose sensory disorders were diagnosed as anesthesia dolorosa or SMP. It was proposed that anesthesia dolorosa and SMP, in contrast to hyperalgesia and hyperpathia, were maintained by complex central and autonomic pathologic mechanisms. In agreement with Gregg's findings, other clinical investigators have expressed little optimism for the surgical alleviation of pain when there is evidence for “central maintenance” of the pain complaint.29- 49 Such patients can often be identified by their report of constant pain and the lack of pain relief from local anesthetic blocks proximal to the site of injury.29 Unfortunately, these very same patients often fail to benefit from alternative pharmacologic, physical, and psychological therapies. Accordingly, it has been suggested that the best treatment for the more complex dysesthesias is one of prevention: Any patient who has spontaneous or stimulus-induced pain during a consecutive 3- to 4-week period or “bothersome” paresthesia(s) and areas of total anesthesia 6 months after injury should be evaluated for microsurgery.13,29 The rationale for this recommendation is that the development of pathologic changes within the CNS, which are associated with pain and are refractory to treatment, can be aborted by early surgical intervention. However, there is little scientific evidence to support this position.49 Finally, the authors recognize that the proposed algorithm does not apply to all patients. It does, however, represent an important first step in defining a systematic approach by which high-quality care can be provided to most patients who have experienced orofacial nerve injury and in establishing a hypothetical approach for the purpose of refinement by additional clinical data. Given the growing number of nerve-injured patients presenting to the clinic for evaluation and treatment, the current need for both is unquestionable.