Question 5 of 10

(demo test)

Product Demo for RITE®

Sample Case Description

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A 70-year-old woman is referred to your office by her primary care doctor with a referring diagnosis of trigeminal neuralgia. She tells you that about one month ago she noticed that her left lower lip felt numb when she was drinking from a coffee mug and that these sensory changes have persisted ever since. She describes her left lower lip, and chin, as feeling "dead", "like somebody shot novocaine into that area." She denies any current pain or history of facial pain. She hasn't been to the dentist in almost a year but notes that she always gets a "gold star" from the dentist at her check-ups and has never had dental caries. A complete review of systems is otherwise negative and she is on no prescribed medications. A thorough neurologic examination is only notable for subjective loss of sensation in the distribution described above.

Please note that you will not be able to return to a prior question to provide an answer if you skip ahead. Case questions should be answered in order and you will not be able to move back to answer prior questions provided in the case once you have advanced to the subsequent question.

Sample Case Question 1 of 3

The most appropriate next step in the management of this patient is which of the following?

A. order electromyography and nerve conduction studies

B. query her on whether she is up to date on her cancer screening

C. referral back to her primary care doctor with the good news that she does not have trigeminal neuralgia

D. send her to the emergency room for a stat head CT

E. start carbamazepine 100 mg tid

Heads up! This question and its explanation are locked because of G-type Sample Cases restrictions. Please answer all questions in current sample case to see explanations.

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Category:

Clinical Adult

Topic:

Clinical Adult

High Yield:

No

Your Answer:

U

Correct Answer:

B

Explanation:

This is a fairly classic presentation of a mental mononeuropathy, also known as "numb chin syndrome." While many etiologies exist, the most common etiology is likely iatrogenic (i.e., associated with dental procedures) or a manifestation of a primary dental/maxillofacial pathology (e.g., abscess, mandibular osteomyelitis). However, for the neurologist, and particularly for the RITE and ABPN exams, this syndrome should always elicit the differential of metastatic disease to the mandible from an as of yet unidentified malignancy. In a woman of this age, without past medical history, one would want to ensure that she is up to date on her cancer screening, mammography in particular, given that breast cancer is the most frequent malignancy associated with this disorder in some series.

While electrodiagnostic testing can be routinely performed to evaluate the trigeminal nerve (e.g., blink reflex), the most appropriate diagnostic test to order in this case would be an imaging study (CT and/or MRI) of the mandible/face specifically protocoled to evaluate the mental, and more proximal, trigeminal nerve. It is important to recognize that while lesions are commonly identified near the mental foramen or nearby in the mandible, more proximal lesions of the trigeminal nerve can also result in numb chin syndrome and so the entire course of the nerve should be imaged. While she does not have trigeminal neuralgia, but rather a trigeminal branch mononeuropathy, it would be inappropriate to send the patient back to the referring doctor, who has clearly requested your expertise in identifying the etiology of this woman's syndrome, simply because their working diagnosis was inaccurate. While a prompt CT scan of the face/mandible/skull base certainly may be a reasonable first diagnostic step, there is no indication from the case provided that this patient needs to be sent to the emergency room for imaging. Starting a symptomatic therapy without initiating a workup to identify the etiology is also not appropriate. Furthermore, carbamazepine is unlikely to help the "negative" sensory symptoms present in this case, as it is a medication effective in treating the "positive" symptoms (i.e., lancinating pain) present in conditions such as trigeminal neurlagia. And in an elderly patient this agent is likely to only have adverse effects without any potential benefit. 

Reference: 

Smith RM, Hassan A, Robertson CE. Numb Chin Syndrome. Curr Pain Headache Rep. 2015 Sep;19(9):44.

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