A Case Report of Systemic Intoxication Following Onabotulinum Toxin A Injections Into the Salivary Glands in a Patient With Spinal Muscular Atrophy Type 1.

[BACKGROUND] Sialorrhea in spinal muscular atrophy (SMA) is caused by bulbar weakness, which is aggravated by low oromotor tone rather than saliva overproduction. Botulinum toxin (BTX) reduces sialorrhea by preventing acetylcholine release from the presynaptic secretory parasympathetic nerve terminals. An important adverse effect of BTX, as highlighted in its black box warning, is a systemic spread of BTX leading to botulismlike symptoms including dysphagia, muscle weakness, and death. These symptoms may be more pronounced in peripheral motor neuropathic disorder population such as SMA, whose neuromuscular junction (NMJ) is already dysfunctional.

[METHODS] We report a case of a 17-month-old boy with SMA type 1 following BTX injection for the treatment of sialorrhea.

[RESULTS] The boy developed severe generalized hypotonia, profound dysphagia, decreased airway clearance, and speech difficulty following BTX injection. Full gastric feeding was required. Pyridostigmine was started but with minimal effect. The patient experienced prolonged deleterious side effects of BTX, lasting upward of a year with very slow recovery of limb strengths and oromotor tone.

[CONCLUSIONS] NMJ dysfunction has been well described in SMA. BTX may exacerbate fragile NMJ function by inhibiting acetylcholine release at the presynaptic vesicles. As such, systematic intoxication of BTX can have far-reaching consequences in this population. A strong precaution and cautious weighing of efficacy and risk must be performed before utilizing BTX in the SMA population.