Could This Patient Have Multiple Sclerosis?
Tingling in both lower legs and feet after discontinuing psychotropic medications 3 months ago is unlikely to be MS and should first prompt evaluation for medication-related peripheral neuropathy, particularly given the recent use of divalproex and amphetamines, which can cause peripheral nerve symptoms.
Primary Differential Diagnosis: Medication-Induced Neuropathy
The clinical presentation strongly suggests a peripheral neuropathy rather than MS:
- Bilateral lower extremity tingling in a symmetric distribution is characteristic of peripheral neuropathy, not the typical asymmetric, multifocal CNS lesions seen in MS 1
- Divalproex (valproate) and amphetamines are both associated with peripheral neuropathy and neurological symptoms 2
- The 3-month timeline after medication discontinuation is consistent with medication-induced neuropathy, which can persist or emerge after drug cessation 3
Why MS Is Less Likely
MS diagnosis requires demonstrating inflammatory-demyelinating injury within the CNS that is disseminated in both time and space 1. Key features that argue against MS in this case:
- Isolated sensory symptoms in a symmetric, distal, bilateral pattern (stocking distribution) is typical of peripheral neuropathy, not MS 3, 1
- MS typically presents with discrete episodes of numbness, tingling, weakness, vision loss, gait impairment, incoordination, imbalance, or bladder dysfunction that are asymmetric and involve different CNS locations 1
- No mention of other CNS symptoms such as optic neuritis, brainstem symptoms, bladder dysfunction, or motor weakness that would suggest multifocal CNS involvement 1
Clinical Evaluation Approach
Perform a thorough neurologic examination focusing on:
- Sensory testing in a stocking-glove distribution pattern 3
- Deep tendon reflexes (typically reduced or absent in peripheral neuropathy, preserved or hyperactive in MS) 1
- Motor strength testing (primarily sensory in peripheral neuropathy; MS can have motor involvement) 3
- Gait assessment and coordination testing 1
Consider laboratory evaluation if peripheral neuropathy is suspected:
- Serum B12, folate, thyroid function, glucose/HbA1c 3
- Electrolyte panel 3
- EMG/nerve conduction studies can confirm peripheral neuropathy but are not routinely necessary if clinical diagnosis is clear 3
When to Consider MS Workup
Only pursue MS evaluation if the patient develops:
- Additional CNS symptoms involving different anatomic locations (optic neuritis, brainstem symptoms, bladder dysfunction) 1
- Asymmetric neurological deficits 1
- Episodes separated in time with intervening stability or partial recovery 1
- Upper motor neuron signs (hyperreflexia, spasticity, Babinski sign) 1
If MS remains a consideration, obtain brain and spinal cord MRI looking for periventricular and subcortical white matter lesions, oval-shaped lesions (Dawson's fingers), and gadolinium-enhancing lesions indicating active inflammation 1, 4
Critical Red Flags
Watch for rapid progression of symptoms, development of bulbar dysfunction, or muscle atrophy, which could indicate more serious neurodegenerative conditions and warrant urgent neurological consultation 4
Avoid premature MS diagnosis based solely on isolated sensory symptoms without objective MRI evidence of CNS demyelination and dissemination in time and space 1