The well-equipped practitioner’s office will already contain the supplies and instruments required for examination of the nerve injury patient. Sterile gloves, mouth mirror, tongue blades, cotton swabs, calipers, local anesthetic needles (27 gauge), anesthetic cartridges, and local anesthetic syringe are the basic armamentarium used for nerve testing (Fig. 10.2). A pulp tester (vitalometer) is sometimes used as method of assessing response to pain when evaluating an IAN injury (Fig. 10.3). An algometer can be another way to assess pain response. Thermal discs are utilized by some clinicians to test ­sensory response to temperature change [17]. Semmes-Weinstein monofilaments [63] provide a more accurate and reproducible measure of contact detection (static light touch), although the use of a cotton swab as demonstrated below is adequate in the typical clinical situation.

A regional examination is completed on all patients including the head, eyes, ears, nose, face, temporomandibular joints, neck, oral cavity, pharynx, and neck. Specific components of the screening evaluation for the nerve injury patient are shown in Fig. 10.4. Following recording of the patient’s vital signs, the next step is inspection. If the patient is acutely injured, the examiner looks for evidence of maxillofacial trauma (missile wound, laceration, facial bone fracture, abrasion, or contusion). A nerve injury (transection, avulsion, partial tear, compression, or crushing) may be able to be directly visualized through an open wound or laceration [2]. In other patients, the examiner searches for signs of recent or past injury or surgery (e.g., sutured or healing incisions, scars) or neurotrophic changes of the skin (edema, erythema, ulcerations, hypohidrosis, loss of hair, hypokeratosis) that may develop following sensory loss in that area. The patient with long-standing sensory dysfunction may repeatedly traumatize insensate soft tissues, producing factitious (self-induced) injury (Fig. 10.5). In the neck, scars from previous injury or surgical incisions when stimulated by repeated gentle stroking with the examining finger or a cotton swab may respond with symptoms and signs of sympathetic nervous system hyperactivity (hyperesthesia, sweating, blanching, flushing, skin temperature changes) in the cutaneous area supplied by the injured nerve. Such findings may be diagnostic of sympathetic-mediated pain (SMP; also known as reflex sympathetic dystrophy or complex regional pain syndrome [26]).

Palpation or percussion is done directly over the mandibular retromolar area or the medial ­surface of the mandible adjacent to the third molar tooth (for the LN), over the mental ­foramen either on the skin surface or intraorally between the mandibular premolar teeth (for the MN), beneath the inferior orbital rim on the skin or transorally superior to the maxillary premolar teeth (for the IFN), and at the midpoint of the eyebrow (for the supraorbital nerve (SON)). One of three possible responses, each called a trigger, may be induced in the presence of a nerve injury (Fig. 10.6). First, a painful sensation (often characterized by the patient as an “electric shock”) is induced and is limited to the area of applied stimulation. Second, this painful sensation may radiate from the area of stimulation and proceed distally into the area supplied by the affected nerve (e.g., palpation of the lingual nerve causes ipsilateral painful sensations in the tongue and floor of mouth). Third, nonpainful responses (tingling, crawling, itching) radiate from the area of nerve palpation. In some patients, palpation or percussion over the injured nerve induces no trigger response. Subsequent direct observations of the injured nerve during microsurgical repair usually confirm that the trigger area denotes the site of nerve injury [70]. A painful response without radiation frequently indicates a complete nerve severance with a proximal stump neuroma as the source of the pain. On other hand, a painful response, or a nonpainful response with radiation, in some patients is a sign of partial nerve transection or a neuroma-in-continuity. This sign has been referred to as the Tinel’s sign, and it may indicate regenerating nerve fibers present in the area of palpation, or it may indicate the presence of a neuroma. In other patients with complete nerve severance, there are distally radiating sensations from the trigger area which probably represent phantom pain [33]. Occasionally, a patient with a significant nerve injury fails to give a trigger response to stimulation over the injury site. Therefore, a trigger response should be considered indirect evidence of a significant nerve injury, whereas a lack of response does not rule out the presence of injury.

Percussion of the mandibular teeth may invoke tingling or unpleasant sensations that may or may not radiate from the teeth to the lower lip or chin. Palpation, percussion, or gentle stroking of the lower lip or chin may also cause sensations that radiate to the lower teeth. The significance of these findings in relation to the extent or nature of the injury to the IAN is not well understood [24, 25, 41, 66]. The appearance of the nerve at ­surgery does not always correlate well with the extent of injury implied by results of the clinical examination; examination and neurosensory testing (see below) are less accurate at predicting the extent of IAN injury than that of LN injury [70].

The evaluation of taste sensation requires special equipment (see below), it is a technically demanding endeavor [68], and the results may be difficult to interpret [28]. Most patients who have sustained an LN injury are primarily concerned with lost, altered, or painful general tongue sensation and the sequelae of accidental tongue biting, difficulty chewing food, painful toothbrushing (if there is a trigger area), effects on speech, and interference with the playing of wind musical instruments. Whether or not the patient has altered taste sensation seldom, if ever, influences the surgeon’s decision regarding surgical or other treatment for the injured LN [3, 53]. Therefore, taste testing is not usually included in the routine evaluation of the patient with a peripheral trigeminal nerve injury. In the patient who develops a taste aberration in the absence of known peripheral nerve injury, taste testing may be helpful in documenting whether or not there is an anatomical cause for actual loss of taste function (which might represent a symptom and sign of a brain tumor, for instance) rather than its being due to a side effect of medication (e.g., chlorothiazide diuretics) or to a strictly psychological aberration. The taste buds in the anterior two-thirds of the tongue receive special sensory supply from the chorda tympani fibers that originate in the nucleus of the FN7 and join the LN peripherally before its course to the tongue. Taste buds in the posterior one-third of the tongue are supplied by the glossopharyngeal nerve (GP9). Therefore, application of substances must be carefully confined to one or the other segments of the tongue, and crossover of the substances to the contralateral side must be prevented to allow valid interpretation of the results. Further complicating this special sense is that taste is greatly influenced by the sense of smell (note the common loss of taste sensation during an upper respiratory affliction such as the common cold or rhinitis from allergies). During taste testing, olfaction must be blocked, or nonaromatic substances must be used. Some patients have reported no change in taste sensation in instances of documented LN anesthesia [53]. Clinical testing has shown a “remarkable difference” between a patient’s stated impression of his taste perception and his true ability to taste specific substances based on testing [29]. Some patients may not even be aware of significant deficits in taste perception [8]. The ability of the chorda tympani nerve nuclei to regenerate after severance of peripheral axons has been shown to be highly unpredictable and sometimes to a lesser degree than the general sensory nerve nuclei of the trigeminal nerve [23]. Psychological factors not presently known or understood may influence a patient’s perception of taste, whether or not there has been an injury to one of the nerves carrying special sense impulses from the taste buds [52].

If the clinician wishes to evaluate taste sensation, the examination may include either regional testing or whole mouth testing [21]. Regional testing evaluates selected groups of taste buds (i.e., those on the anterior two-thirds or those on the posterior one-third of the tongue) and allows the clinician to differentiate between the special sensory input of the LN and the GP9 [28]. Therefore, regional testing is more valuable when one desires to measure the function of a specific nerve with regards to taste sensation [44]. Whole mouth testing gives a more global and nonspecific overview of the integrity of taste rather than focusing on the specific innervation of selected groups of taste buds. The sense of taste conducted from the taste buds supplied by the chorda tympani branch of the facial nerve via the LN can be tested by applying sweet (sucrose), sour (citric acid), salt (saline), and bitter (quinine) substances to the anterior two-thirds of the tongue [8]. The substances are applied via an enclosed “surface chamber” to confine them to an isolated and discrete area of the tongue [68]. The patient’s eyes are closed and the nares are occluded during the taste applications. The patient is requested to report whether they feel the application of the test substance on the tongue and to identify the specific taste. Findings are graded on a 0–2 scale (2  =  patient feels application and correctly identifies its taste as sweet, sour, salt, or bitter; 1  =  patient feels application, but has no taste identification; 0  =  patient does not feel application and has no taste identification).

Neurosensory testing (NST) includes a group of standardized clinical diagnostic maneuvers designed to evaluate general sensory function in as unbiased a manner as possible. Such testing, although the methods have been characterized as being subjective in that they are influenced by the patient’s level of cooperation and interpretation [65], is reproducible on serial repetition on the same patient by the same or other examiners. The patient who is malingering, is considering a legal action against the practitioner who performed a procedure thought to be responsible for a nerve injury, or is attempting to embellish an application for worker’s compensation for a job-related injury may be a challenge for the clinician who strives to gain an accurate assessment of the level of sensory dysfunction. In some instances, the patient may seek to exaggerate responses to NST (as well as overestimate the severity of symptoms in the history). A patient who complains of symptoms or functional impairment in distinct disproportion to the results of the clinical examination should arouse suspicion that there is a “hidden agenda” involved with attempts to manipulate the results of the neurosensory testing. By randomizing the order, type, or location of stimulus application (or in some instances not applying the stimulus at all) and carefully observing the patient’s nonverbal responses (e.g., promptness or lack of response or withdrawal from a stimulus) or “body language” (disinterested facial expression, grimacing or sneering, failure to make eye contact during the evaluation, nervous hand mannerisms, excessive facial sweating, facial flushing or pallor), the astute examiner may be able to recognize inappropriate behavior and prevent patient attempts to distort or misrepresent the results.

The material presented below is a summary of methods used by clinicians experienced in the field of peripheral nerve injuries [16, 22, 36, 43, 48, 49, 67]. The rationale for their use and the validity of their results have been established in various studies [19, 70].

During the neurosensory examination, the patient is seated comfortably in a quiet room, and most maneuvers are performed with the patient’s eyes closed. When the patient’s lips are being tested, they should be separated so that pressure or vibration of applied stimuli is not transferred from the stimulated lip to the opposite lip. The specific tests and responses are described in detail to the patient so that he understands and is able to make the appropriate responses during NST. The examiner explains each step beforehand with reassurance that the stimulus will be applied gently and with due concern for any areas of pain or hypersensitivity that were described in the patient’s history or elicited in the general head, neck, and oral examination. The contralateral normal side is always tested first to determine the patient’s normal “control” responses in order to establish a baseline for examination of the abnormal side.

The NST begins by determining the area of altered sensation with the marching needle technique. A 27-gauge local anesthetic needle is advanced from a normal area adjacent to the area of sensory dysfunction indicated by the patient’s history. The needle contacts the surface mucosa or skin lightly at 1–2 mm intervals until the patient indicates (by raising the ipsilateral hand) the location where the sensation of the needlepoint begins to change. This process is repeated until the border of the entire area of altered sensation is determined. Within this area when the injured nerve has lost all ability to transmit impulses, there will be an intermediate zone adjacent to the border where there is a decrease in the appreciation of the stimulus (hypoesthesia in which sharp becomes “dull,” but contact is still perceived by the patient) [11]. This is probably due to crossover sensory fibers from an adjacent or contralateral nerve [20]. Further into the affected area (usually within a few millimeters), the patient fails to feel the stimulus at all (anesthesia). If this area is on the skin, it is indicated with a colored erasable marking pen. The markings can later be easily removed with alcohol or orange solvent (Fig. 10.7). The NST then begins, first, on the contralateral normal side (e.g., the right lower lip to establish normal responses for that patient) and then on the ipsilateral side (the left lower lip with altered sensation) to ascertain the level of abnormal responses. In a patient with bilateral nerve injuries, an adjacent normal area is chosen for control responses (e.g., for bilateral IAN injuries, the vermilion border of the normal upper lip for comparison with the abnormal lower lip; for bilateral IFN injuries, the normal lower lip vermilion border for comparison with the abnormal upper lip; for bilateral LN injuries, the normal lower labial mucosa for comparison with bilateral lingual gingiva and tongue numbness).

When performing NST, it is important to understand the concept of threshold of response [60]. When a stimulus (such as a needle) is applied to the skin or mucosal surface, it is done initially with little minimal pressure and with no indentation of the surface tissue. If the patient responds to the stimulus (raised ipsilateral hand), it is noted that the response was at the normal threshold. If the patient does not feel the stimulus, then the stimulus is applied again with just enough additional pressure to produce indentation, but not piercing, of the skin or mucosa. If the patient now responds to the stimulus, this response is noted to be at an increased threshold. This is an abnormal response indicating that the nerve has sustained injury but still has the ability to transmit electrical impulses from the periphery to the CNS. However, that ability is compromised in terms of the numbers of axons able to transmit and/or their speed of transmission (Fig. 10.8). If the patient still fails to respond at the increased threshold, it is noted that there is no response (NR), and no further additional pressure is applied to the stimulus. To further increase the pressure applied to the stimulus (i.e., needle) at this juncture will induce penetration of the skin or mucosa with bleeding and will add no helpful information. This concept produces a simple, but accurate and reproducible, measurement of responses to static light touch and pain (level B and level C testing, see below). Other methods will be described as well.

The NST of a patient with decreased altered sensation differs from that of the patient who complains of unpleasant altered sensation. The goals for diagnosis and treatment are not the same for these two categories of sensory nerve injury patients. In the former (decreased altered sensation), the clinical objective is to improve or restore lost sensory function, whereas, in the latter, reduction or relief of pain is the primary reason for treatment. Therefore, the evaluation of each of these two types of sensory nerve injury patients is discussed separately.