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).