How to Thoroughly Assess Altered Sensation: A Detailed Guide for Medical Students and Doctors

Altered sensation, or sensory disturbance, is a common clinical presentation that can arise from a wide range of conditions. It may manifest as numbness, tingling, burning, or a loss of sensation, and can affect any part of the body. For medical students and healthcare professionals, accurately assessing altered sensation is crucial for diagnosis and management. This comprehensive guide will delve into the essential aspects of assessing altered sensation, including the clinical approach, differential diagnosis, and key considerations for patient care.

Understanding Sensation and Its Pathways

Before assessing altered sensation, it's vital to understand the basics of the sensory pathways. The somatosensory system is responsible for transmitting sensory information from the body to the brain. It includes:

1. Peripheral Nerves: These nerves transmit sensory signals from the skin, muscles, and joints to the spinal cord.
2. Spinal Cord: The sensory signals travel up the spinal cord to the brainstem.
3. Brainstem and Thalamus: Sensory information is relayed through the brainstem and thalamus before reaching the cerebral cortex.
4. Cerebral Cortex: The primary sensory cortex in the brain interprets these signals, allowing us to perceive sensations such as touch, temperature, and pain.

Understanding these pathways helps in pinpointing the location of a lesion or dysfunction that could be causing altered sensation.

Clinical Approach to Assessing Altered Sensation

1. Patient History

The first step in assessing altered sensation is obtaining a detailed patient history. Important aspects to explore include:

• Onset and Duration: When did the symptoms start? Are they acute or chronic? Is the sensation constant or intermittent?
• Character of Sensation: Is the sensation described as numbness, tingling, burning, or something else?
• Location: Which part of the body is affected? Is it unilateral or bilateral? Does it follow a dermatome or nerve distribution?
• Aggravating and Relieving Factors: Are there any activities or positions that worsen or alleviate the symptoms?
• Associated Symptoms: Is there weakness, muscle atrophy, pain, or autonomic dysfunction?
• Medical History: Past medical conditions, such as diabetes, multiple sclerosis, or previous trauma, can provide crucial clues.
• Medications and Toxins: Some medications and toxins can cause neuropathy, leading to altered sensation.

2. Physical Examination

A thorough physical examination should follow the history taking. Key components include:

• Inspection: Look for any signs of muscle wasting, skin changes, or deformities.
• Palpation: Check for tenderness or abnormal masses.
• Sensation Testing: This is the cornerstone of assessing altered sensation. Use different stimuli to test various sensory modalities:
  • Light Touch: Use a cotton swab or your fingertip to gently touch the skin.
  • Pinprick: A pin or sharp object can be used to test pain sensation.
  • Temperature: Use cold and warm objects to assess the ability to differentiate temperatures.
  • Vibration: A tuning fork applied to bony prominences can test vibration sense.
  • Proprioception: Assess the patient’s ability to detect joint position changes, particularly in the fingers and toes.
• Reflex Testing: Reflexes can provide additional information about nerve function. Check deep tendon reflexes, such as the patellar and Achilles reflexes.
• Motor Function: Assess muscle strength, tone, and coordination, as motor deficits can accompany sensory disturbances.

3. Neurological Examination

A focused neurological examination is essential to further assess the extent and distribution of sensory deficits. Important aspects include:

• Dermatomal Distribution: Map the areas of altered sensation to specific dermatomes to help localize the lesion.
• Peripheral Nerve Distribution: Determine if the altered sensation follows the pattern of a specific peripheral nerve.
• Cranial Nerve Examination: In cases where cranial nerve involvement is suspected, such as in trigeminal neuralgia, a thorough examination of the cranial nerves is warranted.

Differential Diagnosis of Altered Sensation

1. Peripheral Neuropathies

Peripheral neuropathies are a common cause of altered sensation and can result from various conditions:

• Diabetic Neuropathy: Often presents as a "glove-and-stocking" distribution of numbness and tingling in the hands and feet.
• Alcoholic Neuropathy: Chronic alcohol use can lead to peripheral nerve damage, resulting in similar symptoms.
• Guillain-Barré Syndrome: An acute autoimmune condition causing ascending paralysis and sensory disturbances.
• Carpal Tunnel Syndrome: Compression of the median nerve in the wrist leads to altered sensation in the thumb, index, and middle fingers.

2. Central Nervous System Disorders

Altered sensation can also result from lesions in the central nervous system:

• Multiple Sclerosis: Demyelinating plaques in the CNS can cause sensory disturbances, often with a patchy distribution.
• Stroke: Depending on the area of the brain affected, a stroke can lead to sensory deficits on one side of the body.
• Spinal Cord Lesions: Trauma, tumors, or infections affecting the spinal cord can result in sensory changes below the level of the lesion.

3. Systemic Conditions

Several systemic conditions can lead to altered sensation:

• Vitamin B12 Deficiency: Causes subacute combined degeneration of the spinal cord, leading to sensory and motor deficits.
• Hypothyroidism: Can cause a peripheral neuropathy that results in numbness and tingling.
• Amyloidosis: The deposition of amyloid proteins can lead to nerve damage and sensory disturbances.

4. Toxins and Medications

Certain toxins and medications are known to cause sensory neuropathies:

• Chemotherapy Agents: Drugs like cisplatin and vincristine can lead to peripheral neuropathy.
• Heavy Metals: Exposure to lead, arsenic, or mercury can result in sensory disturbances.
• Antiretroviral Drugs: Some medications used to treat HIV can cause peripheral neuropathy.

Investigations for Altered Sensation

Once a clinical assessment suggests a particular diagnosis, appropriate investigations can help confirm it:

1. Blood Tests

• Complete Blood Count (CBC): To rule out anemia or infection.
• Blood Glucose Levels: To check for diabetes.
• Vitamin B12 and Folate Levels: To assess for nutritional deficiencies.
• Thyroid Function Tests: To evaluate for hypothyroidism.
• Electrolytes: To detect any imbalances that could affect nerve function.

2. Neuroimaging

• MRI of the Brain and Spinal Cord: Can detect lesions such as tumors, multiple sclerosis plaques, or spinal cord compression.
• CT Scan: Useful for detecting strokes or other brain lesions.

3. Nerve Conduction Studies (NCS) and Electromyography (EMG)

• NCS: Measures the speed and strength of signals traveling through the nerves, helping diagnose peripheral neuropathies.
• EMG: Evaluates the electrical activity of muscles, useful for diagnosing conditions affecting the motor neurons.

4. Lumbar Puncture

• Cerebrospinal Fluid (CSF) Analysis: Can help diagnose conditions like multiple sclerosis, infections, or Guillain-Barré syndrome.

Management of Altered Sensation

The management of altered sensation depends on the underlying cause:

1. Pharmacological Treatment

• Pain Management: Neuropathic pain can be treated with medications such as gabapentin, pregabalin, or tricyclic antidepressants.
• Addressing the Underlying Condition: Treating the root cause, such as controlling blood sugar in diabetic neuropathy or supplementing vitamin B12 in deficiency states, is crucial.

2. Physical Therapy

Physical therapy can help improve mobility and function in patients with sensory deficits. Techniques include:

• Strengthening Exercises: To improve muscle function and prevent atrophy.
• Balance Training: To reduce the risk of falls in patients with proprioceptive deficits.
• Sensory Re-education: Helps patients adapt to changes in sensation.

3. Surgical Intervention

In some cases, surgery may be required, such as decompression surgery for carpal tunnel syndrome or spinal surgery for cord compression.

Prognosis and Follow-Up

The prognosis for patients with altered sensation varies widely depending on the cause. Conditions like diabetic neuropathy may require long-term management, while others, like Guillain-Barré syndrome, can improve significantly with treatment. Regular follow-up is essential to monitor progression, adjust treatment plans, and manage any complications.