Numbness, Tingling, and Altered Sensation

Introduction

Altered sensation is a common presenting complaint in Canadian primary care and emergency settings. For MCCQE1 preparation, it is crucial to differentiate between central and peripheral causes, recognize neurological emergencies, and apply a cost-effective, evidence-based diagnostic approach aligned with Choosing Wisely Canada.

The spectrum of symptoms includes:

Paresthesia: Spontaneous, abnormal sensations (e.g., “pins and needles”).
Dysesthesia: Unpleasant or painful abnormal sensations.
Anesthesia: Complete loss of sensation.
Hypoesthesia: Diminished sensation.

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Canadian Epidemiology Note: Canada has one of the highest rates of Multiple Sclerosis (MS) in the world. Any young patient presenting with transient or progressive sensory deficits (especially lasting >24 hours) should trigger a high index of suspicion for MS in the MCCQE1 context.

Clinical Approach to Altered Sensation

A systematic approach is required to localize the lesion (Neuroanatomy is key for the MCCQE1).

Step 1: Characterize the Symptoms

Determine the nature of the sensation. Is it positive (tingling, burning) or negative (numbness, loss of feeling)?

Positive phenomena generally suggest nerve irritability / hyperexcitability.
Negative phenomena suggest conduction block or axonal loss.

Step 2: Define the Distribution

The pattern of sensory loss is the most powerful localizing tool.

Hemisensory loss: Contralateral brain lesion (Thalamus/Cortex).
Sensory level: Spinal cord lesion (check dermatomes).
Dermatomal: Nerve root (Radiculopathy).
Stocking-glove: Length-dependent polyneuropathy (Diabetes, Alcohol).
Mononeuropathy: Specific nerve distribution (e.g., Median nerve in Carpal Tunnel).

Step 3: Assess Associated Symptoms

Motor weakness: Suggests involvement of motor fibers (root, plexus, nerve) or central motor pathways.
Pain: Is it radicular (shooting) or local?
Autonomic symptoms: Orthostasis, urinary retention (suggests small fiber or cord involvement).
Constitutional symptoms: Weight loss, night sweats (malignancy, vasculitis).

Step 4: Review Past Medical History & Medications

Diabetes: Most common cause of peripheral neuropathy in Canada.
Alcohol use: Thiamine deficiency.
Medications: Chemotherapy (Taxanes, Platinum drugs), Metronidazole, Isoniazid.
Diet: B12 deficiency (Vegans, Pernicious Anemia).

Physical Examination

For the MCCQE1, focus on distinguishing the sensory modality involved, as this separates the dorsal column from the spinothalamic tract.

Sensory Modalities

Tract	Modality	Testing Method	Clinical Significance
Dorsal Column	Vibration, Proprioception, Fine Touch	128 Hz tuning fork, Joint position sense	Deficits cause sensory ataxia, Romberg sign positive. Common in B12 deficiency, Tabes Dorsalis.
Spinothalamic	Pain, Temperature, Crude Touch	Pinprick (safety pin), Cold sensation	Deficits cause loss of protective sensation. Common in Syringomyelia, Brown-Séquard.

Red Flags: “The Do Not Miss” List

🚩 Red Flags Requiring Urgent Imaging/Referral

Cauda Equina Syndrome: Saddle anesthesia, bowel/bladder dysfunction, bilateral sciatica.
Spinal Cord Compression: Sensory level, hyperreflexia below lesion, Babinski sign.
Acute Stroke: Sudden onset hemisensory loss (call stroke code).
Guillain-Barré Syndrome: Ascending paresthesias followed by weakness and areflexia.

Differential Diagnosis

The differential diagnosis is best organized anatomically.

Central Nervous System

1. Brain (Cortex/Thalamus)

Stroke/TIA: Acute onset, contralateral deficits.
Tumor: Progressive, headache, morning nausea.
Multiple Sclerosis: Plaques in sensory tracts.

2. Brainstem

Wallenberg Syndrome (Lateral Medullary): Ipsilateral facial numbness + Contralateral body numbness (crossed signs).

3. Spinal Cord

Transverse Myelitis: Bilateral sensory level.
Brown-Séquard: Ipsilateral vibration/proprioception loss + Contralateral pain/temp loss.
Syringomyelia: “Cape-like” distribution of pain/temp loss (central cord).
Subacute Combined Degeneration: B12 deficiency (Dorsal columns + Corticospinal tracts).

Common Abbreviations


CTS  : Carpal Tunnel Syndrome
DSPN : Distal Symmetric Polyneuropathy
EMG  : Electromyography
NCS  : Nerve Conduction Studies
MS   : Multiple Sclerosis
TIA  : Transient Ischemic Attack
MRI  : Magnetic Resonance Imaging

Investigations

For MCCQE1, select investigations based on the pre-test probability. Avoid “shotgun” testing.

Laboratory Workup

Standard: CBC, electrolytes, creatinine, HbA1c (Diabetes), fasting glucose.
Nutritional: Vitamin B12 (plus Methylmalonic acid if borderline).
Other: TSH, SPEP (if suspicion of paraproteinemia), ANA/ENA (if vasculitis suspected).

Electrophysiology

Nerve Conduction Studies (NCS) / EMG: The gold standard to differentiate:
- Axonal vs. Demyelinating.
- Radiculopathy vs. Plexopathy vs. Neuropathy.

Imaging

MRI Spine: Indicated for suspected radiculopathy (if conservative management fails or red flags present), myelopathy, or cauda equina.
MRI Brain: Indicated for suspected MS, stroke, or tumor.

Canadian Guidelines & Management

1. Choosing Wisely Canada

Lower Back Pain: Do not order imaging for lower back pain within the first 6 weeks unless red flags are present. Most radiculopathies resolve spontaneously.
Carpal Tunnel: Do not order EMG/NCS for typical Carpal Tunnel Syndrome unless diagnosis is unclear or surgery is being considered.

2. Diabetes Canada Guidelines (Neuropathy)

Screening: All individuals with Type 2 Diabetes should be screened for distal symmetric polyneuropathy at diagnosis and annually thereafter using the 10g Semmes-Weinstein monofilament.
Management:
- Glycemic control (prevents progression).
- Foot care education (prevents ulcers).
- Pharmacotherapy for pain.

3. Pharmacotherapy for Neuropathic Pain

Canadian guidelines recommend a stepwise approach.

First Line

Gabapentinoids (Gabapentin, Pregabalin)

TCA (Amitriptyline, Nortriptyline)

SNRI (Duloxetine, Venlafaxine)

Second Line

Tramadol

Topical agents (Lidocaine, Capsaicin)

Third Line

Opioids (Use with caution)

Cannabinoids (Emerging evidence)

Key Points to Remember for MCCQE1

B12 Deficiency: Can cause irreversible neurological damage before anemia appears. Always check B12 in patients with proprioceptive loss or dementia.
Cauda Equina: This is a surgical emergency. MRI is the investigation of choice.
Meralgia Paresthetica: Compression of the lateral femoral cutaneous nerve (tight belts, obesity, pregnancy). Purely sensory (anterolateral thigh).
Double Crush Syndrome: A proximal nerve compression (neck) makes the distal nerve more susceptible to compression (wrist).
Canadian Context: Be aware of wait times. Triaging patients for MRI based on urgency (e.g., progressive motor deficit vs. stable sensory loss) is a tested concept.

Sample Question

Clinical Scenario

A 62-year-old male presents to his family physician complaining of burning pain and numbness in both feet, which has been gradually worsening over the past year. He describes the sensation as “walking on cotton wool.” He has a history of hypertension and obesity. He denies back pain, bowel or bladder incontinence, or upper extremity symptoms. Physical examination reveals decreased sensation to pinprick and vibration in a stocking distribution up to the mid-calves bilaterally. Ankle reflexes are absent bilaterally.

Which one of the following is the most appropriate initial diagnostic investigation?

Options

A. MRI of the lumbar spine
B. Nerve conduction studies (NCS)
C. Fasting blood glucose and Hemoglobin A1c
D. Serum Vitamin B12 levels
E. Doppler ultrasound of the lower extremities

Click to reveal answer and explanation

Explanation

The correct answer is:

C. Fasting blood glucose and Hemoglobin A1c

Detailed Explanation: The clinical presentation is classic for Distal Symmetric Polyneuropathy (DSPN), often described as a “stocking-glove” distribution. The most common cause of this in the Canadian population is Diabetes Mellitus.

Option C: This patient has risk factors (obesity, hypertension, age) and symptoms highly suggestive of diabetic neuropathy. Screening for diabetes is the most high-yield initial step to identify the underlying etiology.
Option A: MRI Lumbar spine is indicated for radiculopathy (dermatomal pattern) or spinal stenosis (neurogenic claudication). This patient’s symptoms are length-dependent and bilateral, not dermatomal.
Option B: NCS confirms the diagnosis and type of neuropathy but does not identify the cause. It is usually reserved for atypical cases or when the diagnosis is unclear after initial metabolic workup.
Option D: Vitamin B12 deficiency is a differential, but diabetes is statistically much more common. B12 levels would be part of the workup if glucose testing is normal or if there are specific risk factors (metformin use, veganism, gastric surgery).
Option E: Doppler is used for peripheral arterial disease (PAD). While PAD causes claudication and pain, the “cotton wool” sensation and loss of vibration/reflexes are neurological, not vascular signs.

CanMEDS Role: Medical Expert (Prioritizing investigations based on epidemiology and clinical presentation).

References

Diabetes Canada Clinical Practice Guidelines Expert Committee. (2018). Neuropathy. Canadian Journal of Diabetes.
Choosing Wisely Canada. (2023). Family Medicine: Imaging for Low Back Pain.
Kasper, D. L., et al. (2022). Harrison’s Principles of Internal Medicine, 21st Edition. McGraw Hill.
Medical Council of Canada. (2023). MCCQE Part I Objectives: Numbness, tingling, altered sensation.
Public Health Agency of Canada. (2020). Mapping Connections: An understanding of neurological conditions in Canada.