Diplopia as the primary presentation of foodborne botulism.

Foodborne botulism is a serious condition caused by Clostridium botulinum neurotoxin. Clinically, botulism presents as bilateral cranial nerve neuropathy and descending paralysis. We report a unique presentation of botulism to remind clinicians of this potentially fatal condition. In this observational case report initial evaluation showed only esodeviation. This progressed to unilateral cranial nerve six (CN VI) paresis along with systemic signs. Clinical diagnosis was made based on in-depth history and concurrent symptoms in three other patients. Foodborne botulism presenting as diplopia and unilateral motility deficits is rare and can represent a diagnostic and therapeutic challenge to the ophthalmologist.

Introduction

Foodborne botulism is caused by ingestion of preformed botulinum neurotoxins (BoNTs) elaborated by the organism Clostridium botulinum.[1] BoNTs are the most potent toxin known and are an important disease causing and potential bioterrorism agent.[1]

Botulism presents as bilateral cranial nerve neuropathy[2] progressing to descending symmetric flaccid paralysis that can result in ventilatory dysfunction.[3] Urgent recognition is essential as untreated botulism has a mortality of 40–50%.[4] Clinical diagnosis can be difficult as differential diagnosis is extensive. Treatment involves supportive care and early intravenous administration of antitoxin.[5]

We herein present a case of foodborne botulism initially presenting as diplopia.

Case Report

A 37-year-old Iranian man presented to the ophthalmology department with complaint of binocular horizontal diplopia worse in right gaze for 1 day. He noted accompanying nausea without vomiting. Medical history was not significant. The patient was afebrile, vital signs were stable, and a general physical examination including neurologic exam was normal. On ophthalmologic examination, pupils were equal round and reactive to light and accommodation, ptosis was absent, best-corrected visual acuity was 20/20 OU at distance and J1 on a the Jaeger card indicating preserved near visual acuity. Ocular pressures were 15 OU by applanation. Dilated fundus exam with indirect ophthalmoscopy revealed a healthy optic nerve and fundus OU. Esodeviation of 10–15 prism diopters was measured in distance fixation, worse in right gaze. Brain computed tomography (CT) scan and magnetic resonance imaging (MRI) showed no acute intracranial abnormalities. Outpatient follow-up was advised.

The patient returned to the ophthalmology clinic 3 days later with persistent diplopia and nausea. Visual acuity, ocular pressures, and dilated fundus exam were within normal limits OU. A Hess chart test showed significant restriction of the right eye in lateral gaze [Figure 1]. Right lateral rectus paresis was diagnosed on the basis of this finding. Two days later, symptoms progressed to slurred speech, dysphagia, dyspnea, headache, vertigo, and the patient was admitted to the intensive care unit. Pupils were dilated and minimally reactive. Ocular motility exam showed worsening esodeviation in right gaze and total right lateral rectus paralysis with preserved forced duction. Neurologic exam showed normal deep tendon reflexes and absent localizing deficits, tetany, or fasciculations.

Figure 1

Hess chart. The constricted right eye field demonstrates lateral rectus underaction. There is contralateral medial rectus overaction. Very mild left lateral rectus underaction and contralateral overaction is present. The central point is shifted in both eyes indicating diplopia in primary gaze

The basic metabolic panel was within normal limits and complete blood count revealed white blood cell count 5×103/L, within the normal range. Spinal fluid assay showed normal opening pressure, glucose level, and absent erythrocytes, leukocytes, and bacteria. Repeat brain MRI and CT showed no acute intracranial processes. Edrophonium (Tensilon) challenge was unremarkable. Urine drug screen was negative.

Respiratory paralysis progressed and the patient was intubated, sedated, and mechanically ventilated. He was maintained in the intensive care unit and stabilized over the next few days. In the interim, three other patients were admitted with high clinical suspicion for botulism. On further questioning, the patient reported he was employed as manager of a restaurant where the three other patients had dined. He had also dined at his restaurant prior to symptom onset. All had eaten canned fish.

The diagnosis of botulism was supported by electromyography (EMG) with repetitive muscle stimulation at 20–50 Hz, which showed augmentation of potentials. Botulinum antitoxin was administered and symptoms improved overnight. The patient was discharged after 10 days and follow-up visits for 3 months showed resolution of diplopia and other neurologic signs.

Discussion

Botulism is rare but potentially serious. C. Botulinum causes disease in three ways: food borne botulism, infantile botulism, and wound botulism.[6] In the United States, 112 cases of botulism were reported in 2010. 8% of these were foodborne. BoNT is produced in an anaerobic environment most often described with home canned foods.[1] BoNT is highly potent and exhibits action at the presynaptic membrane of the neuromuscular junction by preventing release of acetylcholine, thus inhibiting neuromuscular conduction.[2] This most often presents as acute bilateral cranial nerve neuropathy causing dry mouth, dysphagia, slurred speech, ptosis, and ophthalmoplegia progressing to descending symmetric paralysis. Patients are afebrile and conscious, although they may be lethargic secondary to neuropathy.[2] Death occurs from paralysis of the respiratory muscles.[3]

Ocular symptoms are rarely the initial sign in isolation of other symptoms. In a recent report, 56% of patients with botulism displayed systemic signs prior to ocular and in 33% of patients ocular and systemic symptoms were concurrent. Only 2 of 18 (11%) showed ocular signs initially.[7] Of ocular findings, blurred vision is the most common (89–100%) followed by ptosis (80%).[37] Observed extraocular muscle dysfunction is rare and when described is bilateral.[3] Our patient presented with diplopia and was found to have esodeviation at distance fixation worse in right gaze progressing to an ipsilateral right lateral rectus paresis.

The diagnosis of botulism remains clinical. Diagnosis can be confirmed by identification of toxin through enzyme linked immunosorbent assays, electrochemiluminescent tests, and mouse inoculation trials.[6] These studies are limited by variation in toxin levels and timeliness of specimen collection.[1] Clinical diagnosis can be challenging as manifestations of botulism are similar to Guillain–Barre, myasthenia gravis, tick paralysis, diphtheria, poliomyelitis, Lambert Eaton syndrome, or medication and drug toxicities. Diagnosis can be aided by exclusionary studies such as edrophonium (Tensilon) challenge, serum toxicology screens, lumbar puncture with ancillary studies, and brain imaging (CT/MRI). EMG can also aid diagnosis.[3] Our patient's clinical picture suggested botulism. This diagnosis is supported by rapid repetitive EMG (20–50 Hz) with augmentation of action potentials characteristic to pathology affecting the presynaptic membrane.

Treatment consists of supportive measures and ventilatory support. Trivalent (types A, B, and E) equine-derived antitoxin remains the standard medical therapy and functions to eliminate the free toxin subtypes most often implicated in human disease before they bind the presynaptic membrane.[8] Optimal benefit is attained from timely clinical diagnosis of botulism and administration of agent.[9] Our patient displayed improvement of clinical symptoms following administration of antitoxin further supporting diagnosis of botulism.

We have reported an unusual presentation of botulism. Ocular findings are rarely the initial sign; when present are most often ptosis or blurred vision and are usually symmetric. Fortunately, this patient received supportive care and the diagnosis of botulism was made in time to administer trivalent antitoxin. The BoNT is potent and represents a serious disease causing and potential bioterrorism agent. It is important for the ophthalmologist to keep botulism on the differential diagnosis for new-onset diplopia, ptosis, or oculomotor dysfunction.