In a 73-year-old man with intermittent right-hand numbness and tingling for about one month without weakness, what diagnostic tests should be ordered?

Diagnostic Workup for Unilateral Hand Numbness and Tingling in a 73-Year-Old Man

Begin with nerve conduction studies and electromyography as the first-line diagnostic test to differentiate between cervical radiculopathy, peripheral nerve entrapment (carpal tunnel or ulnar neuropathy), and polyneuropathy. 1

Initial Clinical Assessment

Before ordering tests, perform a focused neurological examination to guide your diagnostic approach:

• Test for loss of protective sensation using a 10-g monofilament, which is the most useful screening test for peripheral neuropathy 2
• Assess tendon reflexes, as reduced reflexes are highly specific (81-99%) for radiculopathy 3
• Perform somatosensory testing (pinprick, temperature, vibration with 128-Hz tuning fork), though sensitivity is limited (25-52%) 3
• Examine for motor weakness, as progressive weakness is a red flag requiring urgent imaging 1

Primary Diagnostic Testing

Electrodiagnostic Studies (First-Line)

Nerve conduction studies with electromyography should be performed first because they can:

• Differentiate C7 cervical radiculopathy from ulnar neuropathy at the elbow 1
• Identify brachial plexopathy as a distinct entity 1
• Detect polyneuropathy when the clinical picture is unclear 1
• Provide objective evidence of nerve dysfunction with high specificity (98-99%) when all components are considered 3

Laboratory Testing

Order the following blood tests to exclude metabolic and systemic causes:

• Thyroid-stimulating hormone (TSH) to exclude thyroid dysfunction, a common and treatable cause of neurological symptoms in elderly patients 4
• Complete metabolic panel including electrolytes, renal function, liver function, calcium, and glucose to screen for metabolic disturbances 4
• Vitamin B12 level to identify deficiency that may contribute to neurological symptoms 4
• Hemoglobin A1c for diabetes screening, given the patient's age and association with neuropathy 4
• Complete blood count (CBC) to assess for systemic conditions 4

Do not routinely order Lyme serology unless there is relevant exposure history or other neurological signs 4, and ESR/CRP only if giant cell arteritis or inflammatory conditions are suspected 4.

Advanced Imaging (Conditional)

When to Order MRI

Proceed to cervical spine MRI only if:

• Electrodiagnostic studies suggest radiculopathy 1
• Symptoms persist despite normal electrodiagnostic results 1
• Red flags are present: progressive motor weakness, constitutional symptoms (fever, weight loss), or history of malignancy 1

Specialized Imaging Considerations

If brachial plexopathy is suspected (based on electrodiagnostic findings showing multi-nerve-territory involvement or scapular pain):

• Order dedicated MRI of the brachial plexus using orthogonal oblique planes with T1, T2, fat-saturated T2, and fat-saturated T1 post-contrast sequences 1
• Standard cervical spine MRI may miss brachial plexus pathology 1

If symptoms involve the C8-T1 distribution (medial hand/small finger):

• Consider neurogenic thoracic outlet syndrome 1
• MRI of the chest (without contrast) can assess costoclavicular and interscalene spaces 1

Common Pitfalls to Avoid

• Do not skip electrodiagnostic testing and proceed directly to MRI, as this may lead to unnecessary imaging and missed peripheral nerve pathology 1
• Do not rely solely on somatosensory testing, as it has poor sensitivity (25-52%) for detecting radiculopathy 3
• Do not assume a single nerve distribution without electrodiagnostic confirmation, as 40% of patients with upper extremity neurological disturbance have involvement of multiple segments 5
• Do not overlook metabolic causes, particularly thyroid dysfunction and vitamin B12 deficiency, which are treatable causes of neuropathy in elderly patients 4

Clinical Reasoning Algorithm

1. Perform focused neurological examination → Document specific deficits
2. Order electrodiagnostic studies → Localize lesion (root, plexus, or peripheral nerve)
3. Order laboratory panel → Exclude metabolic/systemic causes
4. If radiculopathy confirmed or red flags present → Order cervical spine MRI
5. If plexopathy suspected → Order dedicated brachial plexus MRI
6. If all tests normal and symptoms persist → Consider small fiber neuropathy with skin biopsy 2