What is the diagnosis and treatment for an adult patient with memory loss, tingling in both lower legs, back, and arms, potentially with a history of neurological or chronic conditions?

Diagnostic and Management Approach for Memory Loss with Widespread Paresthesias

This presentation requires urgent evaluation for vitamin B12 deficiency, which classically causes both cognitive impairment and peripheral neuropathy affecting multiple limbs, and should be assessed immediately alongside formal cognitive testing and comprehensive metabolic workup to exclude reversible causes before attributing symptoms to primary dementia.

Immediate Diagnostic Priorities

Laboratory Evaluation for Reversible Causes

• Obtain vitamin B12 level, homocysteine, complete blood count, comprehensive metabolic panel, thyroid function (TSH), erythrocyte sedimentation rate, and C-reactive protein 1
• Vitamin B12 deficiency is a critical reversible cause that presents with both memory impairment and peripheral neuropathy (tingling in extremities), making it the most likely unifying diagnosis for this symptom constellation 1
• Evaluate for diabetes, as it represents both a vascular risk factor for cognitive decline and a common cause of peripheral neuropathy 2, 1

Formal Cognitive Assessment

• Conduct validated neuropsychological testing using Montreal Cognitive Assessment (MoCA), which is more sensitive than MMSE for detecting mild cognitive impairment 2, 1
• Assess episodic memory specifically, as this is the most characteristic domain for patients who later progress to Alzheimer's disease 1
• Evaluate other cognitive domains including executive functions, speech, spatial skills, and attention to determine the pattern of impairment 1

Functional Status Evaluation

• Determine degree of functional impairment using validated scales such as Functional Activities Questionnaire (FAQ) 1
• The distinction between mild cognitive impairment (MCI) and dementia hinges on whether basic activities of daily living (ADL) are preserved—MCI patients have mild disturbances in complex tasks (instrumental ADL) but preserved basic ADL 2, 1

Neurological Workup for Paresthesias

Vascular Risk Assessment

• Evaluate history of stroke or transient ischemic attack, hypertension, hyperlipidemia, and diabetes, as these are risk factors for both vascular cognitive impairment and peripheral neuropathy 1, 3
• Multiple vascular risk factors dramatically increase stroke risk and can cause both cognitive decline and neurological symptoms 3

Exclude Other Neurological Causes

• Assess for recent head trauma, which can cause both cognitive impairment and neurological symptoms 1, 4
• Evaluate for untreated sleep apnea, which is associated with cognitive disorders 2, 1
• Review all medications, particularly anticholinergic and sedative agents, which can cause cognitive impairment and neurological side effects 3, 5

Neuroimaging

• Perform brain MRI (or CT if MRI contraindicated) to exclude vascular lesions, tumors, hydrocephalus, hemorrhages, and structural abnormalities 1, 6
• MRI may reveal medial temporal lobe atrophy (marker of Alzheimer's disease) or vascular lesions contributing to cognitive decline 1
• Look for symmetric bilateral abnormalities that might suggest inflammatory or metabolic processes 6

Critical Diagnostic Pitfalls

Mixed Presentations Requiring Careful Assessment

• First major psychiatric episodes at advanced age, including new depression or anxiety, warrant comprehensive cognitive assessment as they may signal underlying dementia 2, 7
• Depression-related cognitive symptoms may resolve with treatment and should be screened using validated tools 3
• Mixed dementia (vascular plus Alzheimer's) is extremely common in elderly patients and can present with both cognitive and neurological symptoms 3

Medication-Induced Symptoms

• Pregabalin and similar medications commonly cause dizziness, somnolence, ataxia, peripheral edema, thinking abnormal (difficulty with concentration/attention), amnesia, confusion, and tremor 5
• If patient is on gabapentinoids or other CNS-active medications, consider these as contributing to both cognitive and sensory symptoms 5

Longitudinal Monitoring

• Conduct serial cognitive assessments using the same instrument at intervals of at least 6 months to reduce practice effect and document progressive decline 1
• Objective evidence of progressive cognitive decline over time is essential for establishing diagnostic accuracy 1

Management Based on Etiology

If Vitamin B12 Deficiency Confirmed

• Initiate B12 replacement immediately, as this is a reversible cause of both cognitive impairment and peripheral neuropathy 1

If Vascular Risk Factors Present

• Monitor and aggressively manage vascular risk factors (hypertension, diabetes, hyperlipidemia), as they impact dementia progression 1, 3
• Consider memantine for vascular cognitive impairment in individual patients 1
• Intensive statin therapy and antiplatelet therapy for secondary stroke prevention if TIA/stroke history present 3

If Mild Cognitive Impairment Diagnosed

• Ensure assessment of caregiver needs in education, support, and respite services 1
• Consider referral to specialists (neurologist, geriatrician, neuropsychologist) for atypical presentations, rapid progression (as in this case with 3-month onset), or complex symptoms 1, 6

If Alzheimer's Disease Confirmed

• Cholinesterase inhibitors (donepezil) for mild to moderate dementia to improve cognitive function and activities of daily living 3
• Memantine for moderate to severe dementia to improve daily functioning and cognitive performance 3