Could electric shock-like sensations in the upper and lower extremities be an adverse effect of mir

Fråga: Could electric shock-like sensations in the upper and lower extremities be an adverse effect of mirtazapine and venlafaxine treatment? The question pertains to a 25-year-old woman who is being treated with venlafaxine slow release 225 mg/d and mirtazapine 30 mg/day because of depression with suicidal ideation. She is also medicating with oxazepam and zolpidem. Doses are described as moderate and not increasing. After several months of treatment, and two months after the latest dose escalation, the patient started complaining of intermittent electric shock-like sensations in her upper or lower extremities, especially during physical exercise. The symptoms can arise in either extremity, and are without any obvious neuroanatomical correlative. There are no concomitant neurological symptoms, and physical examination is unremarkable. Compliance with therapy is unknown.

Sammanfattning: The specific symtomatology of the patient seems not to be previously associated with the relevant medications in the published literature. However, paresthesias in general could be a side effect of venlafaxine or mirtazapine. The possibility of intermittent withdrawal syndrome should be investigated.

Svar: Paresthesias as a general category is described as a common side effect of both mirtazapine and venlafaxine (1,2). No specific association of electric shock-like sensations, such as those described by the patient, to these medications could be found in the literature. However, the syndrome is described as a relatively uncommon symptom of selective serotonin reuptake inhibitor (SSRI) withdrawal (3,4) Since venlafaxine has an effect on serotonin reuptake, one could speculate whether fluctuating diurnal concentrations or intermittent non-compliance could cause withdrawal symptoms. Incorrect handling or breaking of depot capsules could be one mechanism underlying increased diurnal variations in concentration.

The pathophysiology of electric shock-like sensations is unknown. A syndrome of suchlike pain is the Lhermitte sign (shocklike paresthesia spreading down the trunk and lower extremities on neck flexion) which occurs in various myelopathies of the cervical spinal cord. Shock-like sensations in the extremities have been described with various neuropathies, and could be caused by increased mechanosensitivity in the afferent nervous system (5).

It is recommended that this case be reported to the Swedish register of adverse drug effects. Furthermore, serum concentration determinations of mirtazapine and venlafaxine would be helpful in further assessing the cause of the symptomatology of the patient.