A 60-year-old man comes to the office for evaluation of gait imbalance, which he has had for the past 3 days. The patient was hospitalized 2 weeks ago for a complicated enterococcal diabetic infection of the left foot. He was prescribed ampicillin and gentamicin, which he has continued via home intravenous antibiotic therapy. The patient subsequently developed a constant sensation of objects moving around in his visual field when looking in any direction, which has caused him to feel unsteady. He has no associated nausea or vomiting. The patient has a history of poorly controlled type 2 diabetes mellitus and hypertension. His other medications include lisinopril and basal-bolus insulin therapy. Temperature is 36.7 C (98 F), blood pressure is 140/96 mm Hg, pulse is 80/min, and respirations are 16/min. BMI is 34 kg/m². The left foot wound is healing without discharge or surrounding erythema. Neurologic examination shows 5/5 muscle strength and 2+ reflexes in all extremities. Hearing is decreased in the right ear on whisper test. Rapid head movement away from a fixed target causes eye movement away from the target followed by a horizontal saccade back toward it. Which of the following is the most likely cause of this patient's current symptoms?

Question

Quizplus · Accepted Answer

Explanation: This patient who was recently prescribed gentamicin now has new-onset hearing loss, imbalance, and a sensation of objects moving (oscillopsia). This presentation is consistent with aminoglycoside ototoxicity. The risk of aminoglycoside ototoxicity is increased in patients with bacteremia, hepatic or renal dysfunction, or when used in combination with another potentially ototoxic medication. Aminoglycoside ototoxicity can damage hair cells in the cochlea (causing hearing loss) and/or the vestibular system (causing imbalance). Therefore, patients have varying clinical features, including the following: Bilateral, but not necessarily symmetric, hearing loss (as evidenced by this patient's right > left screening whisper test). Patients with a positive whisper test require a formal audiogram. Imbalance and oscillopsia because bilateral vestibular systems are affected (rather than true vertigo, which generally occurs when 1 side is affected). A positive head thrust test (ie, inability to maintain visual fixation during forced, rapid head movement). This test evaluates the vestibuloocular reflex, which is affected by peripheral but not central vestibulopathies, as seen in this patient. Management of patients with aminoglycoside toxicity requires immediate discontinuation of the medication to prevent further damage. (Choice A) In contrast to this patient, those with benign paroxysmal positional vertigo (BPPV) have brief (<1 minute), episodic vertigo stimulated by specific head movements (eg, rolling over in bed, looking up). In addition, BPPV is not associated with hearing loss and is confirmed with the Dix-Hallpike maneuver (vertigo and nystagmus on quickly lying back into a supine position with the head rotated 45 degrees) rather than the head thrust test. Dix-Hallpike maneuver (Choices B and F) This patient has risk factors for cerebellar stroke and vertebrobasilar insufficiency, which can cause gait imbalance. However, these cause central vertigo and therefore would have a preserved head thrust and no hearing loss. (Choice C) Poorly controlled diabetes can cause autonomic dysfunction (eg, gait imbalance, "dizziness" while standing) due to postural hypotension. However, it does not cause a positive head thrust test, oscillopsia, or hearing loss, making this diagnosis unlikely. (Choice E) Ménière disease is an inner ear disorder characterized by increased endolymph volume and/or pressure (endolymphatic hydrops). It presents with discrete episodes of spinning vertigo (vs constant sensation in this patient) accompanied by hearing loss (which can be progressive) as well as tinnitus or aural fullness (not seen in this patient). In addition, the timeline of symptoms shortly after aminoglycoside therapy makes drug toxicity much more likely. Educational objective: Aminoglycosides can be ototoxic to both the cochlea (resulting in sensorineural hearing loss) and the vestibular system (resulting in imbalance). References: Clinical diagnosis of bilateral vestibular loss: three simple bedside tests. (http://www.ncbi.nlm.nih.gov/pubmed/23277792) Horizontal head impulse test detects gentamicin vestibulotoxicity. (http://www.ncbi.nlm.nih.gov/pubmed/19380701) Hearing loss in patients with vestibulotoxic reactions to gentamicin therapy. (http://www.ncbi.nlm.nih.gov/pubmed/16549744)

A 60-Year-Old Man Comes to the Office for Evaluation of Gait