Discussion
Methadone, a long-acting synthetic opioid agonist, is widely used in the management of opioid dependence and chronic pain (3). While methadone has proven to be an effective treatment option, it is associated with a range of adverse effects, particularly in individuals who are opioid-naive or have a low tolerance to opioids (5). Methadone toxicity can manifest as respiratory depression, cardiac arrhythmias, and, in rare cases, neurological complications such as strabismus (4). The case presented here highlights a rare instance of methadone-induced strabismus and loss of consciousness in a first-time user. The patient, a 21-year-old female with no prior history of opioid use, consumed 5 methadone pills and subsequently developed altered mental status and respiratory depression. Upon regaining consciousness following naloxone administration, the patient reported diplopia and was found to have a significant right exotropia, consistent with lateral strabismus. The exact mechanism underlying methadone-induced strabismus remains unclear, but it is thought to involve the drug’s effects on the central nervous system and the oculomotor nerve (9). Methadone, like other opioids, binds to and activates mu-opioid receptors in the brain, leading to a range of pharmacological effects, including analgesia, sedation, and respiratory depression (11, 12). In the case of strabismus, it is hypothesized that methadone may exert a direct effect on the oculomotor nerve or its nuclei, resulting in a disruption of the normal balance of extraocular muscle tone and alignment (7, 13).
The development of strabismus in the context of methadone toxicity warrants a thorough neurological evaluation to rule out any underlying intracranial pathology or neurotoxicity (10). In the present case, a non-contrast CT scan of the brain was performed, which did not reveal any significant abnormalities. However, it is important to note that the absence of radiographic findings does not preclude the presence of methadone-induced neurotoxicity, as subtle changes may not be detectable on imaging (10, 14).
The management of methadone-induced strabismus primarily involves the treatment of the underlying opioid toxicity. Naloxone, an opioid receptor antagonist, is the mainstay of treatment for methadone overdose (6). In this case, the patient’s altered mental status and respiratory depression were successfully reversed with the administration of naloxone. Supportive care, including intravenous fluid resuscitation and close monitoring, was also provided to ensure the patient’s stability and prevent further complications (4).
The patient’s strabismus was managed conservatively with observation and serial ophthalmological examinations. Over the course of her hospital stay, the right exotropia gradually improved, with a residual deviation of 10 prism diopters at the time of discharge. This spontaneous improvement suggests that the strabismus was likely a transient manifestation of methadone toxicity, rather than a permanent neurological sequela (7).
The present case underscores the importance of recognizing the potential neurological and ocular complications associated with methadone use, particularly in opioid-naive individuals (10) (15). Healthcare providers should be aware of the uncommon manifestations of opioid toxicity, such as strabismus, and promptly initiate appropriate management to prevent long-term morbidity and mortality (4). A comprehensive neurological and ophthalmological evaluation is essential in patients presenting with methadone-induced strabismus to rule out any underlying intracranial pathology and provide targeted treatment (7, 10).
Furthermore, this case highlights the need for increased public awareness regarding the risks associated with recreational methadone use, especially among opioid-naive individuals (3). Education on the potential dangers of methadone, including the risk of overdose and neurological complications, may help to prevent similar cases in the future (10, 15).