Clinical Diagnosis Printable Version of this Page
Clinical Presentation
Physical Examination Signs Helpful in the Diagnosis of Infant Botulism


Because infants are unable to describe their symptoms, the onset of infant botulism can only be detected by careful observation. Usually the first indication of illness is constipation (defined as decreased frequency in defecation), although this sign is frequently overlooked by parents and physicians. Generally, parents first notice that the baby feeds poorly. The breast-feeding mother may notice breast engorgement because the baby’s suck is weak. The infant has become lethargic and listless. Respiratory effort may become shallow and rapid, and the cry is feeble. Drooling may become more noticeable, which is sometimes attributed to teething rather than to dysphagia.


Clinical Presentation

A "catastrophic" presentation of infant botulism with a paucity of the usual clinical signs has also been recognized. See Nevas et al., Journal of Clinical Microbiology, 2005; Mitchell W, Tseng-Ong L, Pediatrics 2005; 116;436-438; and Hurst and Marsh, The Journal of Pediatrics, 122(6):909-911, 1993.

Because botulinum toxin binds at the neuromuscular junction, the toxin produces a flaccid motor paralysis that invariably begins in the bulbar musculature. Somatic musculature is affected next, and patients with rapidly evolving illness may have generalized weakness, hypotonia and respiratory difficulty when first seen.

On initial presentation, the typical patient has some or all of the following findings: ptosis (which may not be evident until the infant’s head is held erect), weak cry, diminished suck and gag, drooling and/or pooling of saliva, dilated and/or sluggishly reactive pupils, disconjugate gaze, blunted facial expression, poor head control, decreased anal sphincter tone, hypotonia and generalized weakness. Deep tendon reflexes may be either normal or decreased. Sensation remains intact, but this may be difficult to demonstrate because of the motor paralysis.

In mild cases or in the early stages of illness, the physical signs of infant botulism may be subtle and easily overlooked. Cranial nerve palsies and the fatigability of muscular function must be elicited by careful examination. Table 1 below describes physical examination techniques which have proved helpful in evaluating these infants.


Test 1. Take the patient to dark room. Shine a bright light into the eye; note quickness of pupillary constriction. Remove the light when constriction is maximal; let the pupil dilate. Then immediately repeat, continuing for 2–3 minutes. Findings: The initially brisk pupillary constriction may become sluggish and unable to constrict maximally. Also, constrictor muscle fatigability may yield a "pseudo" gibbus.

Test 2. Shine a bright light onto fovea, keeping it there for 1–3 minutes even if the infant tries to deviate her/his eyes. Findings: Latent ophthalmoplegia may be elicited, and/or purposeful efforts to avoid the light may diminish, because fatigability with repetitive muscle activity is the clinical hallmark of botulism. Also observe for initial squirming of the extremities that may diminish because of fatigability.

Test 3. Place a clean fifth finger in the infant’s mouth, taking care not to obstruct the airway. Note the strength and duration of the reflex sucking. Findings: The suck is weak and poorly sustained. The gag reflex strength also may be quickly checked (if the infant has not been fed recently).

Establishing the clinical diagnosis is imperative for the timely recognition of infant botulism and treatment with BabyBIG®. However, clinical diagnosis does not obviate the need for prompt collection and submission of a fecal or enema specimen to the appropriate diagnostic laboratory (state lab or CDC depending on your location).

Source: Arnon SS. Infant botulism. pp. 1758-1766 in Feigin RD, Cherry JD, Demmler GJ, Kaplan SL, eds. Textbook of Pediatric Infectious Diseases, Fifth Edition. WB Saunders, Philadelphia, 2004.

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