Sensory Exam by Nerve

Description

• A sensory exam by nerve should include the median, ulnar and radial nerves. The median nerve innervates the volar aspect of the thumb, index, middle, and radial half of the ring finger.  The median nerve also innervates the dorsum of the thumb, index, long, and radial half of the ring finger in the area between DIP joint and at the dorsal base of the fingernail.  The radial nerve innervates the dorsal aspects of the thumb, index, long, and radial half of the ring finger proximal to the thumb IP joint and finger DIP joints. The ulnar nerve innervates the small finger and the ulnar half of the ring finger volarly and the area at the dorsal base of the fingernails distal to DIP joints.¹
• Some of the most common nerve problems involve entrapment of the median (eg, carpal tunnel syndrome), ulnar (eg, cubital tunnel syndrome), radial nerves (radial tunnel syndrome) and nerve lacerations. If a nerve is compressed simultaneously at two different points e.g. neck and carpal tunnel,  or damaged by a peripheral neuropathy like diabetes, then it is called “a double crush” or Double Crush Syndrome.

Pathophysiology

• Compression neuropathy develops when compressive pressures surpass those usually tolerated by any particular nerve.²Compression neuropathies commonly cause decreased sensation and paresthesias in the distribution of the compressed nerve.
• Neuropathy can arise from a variety of sources, including carpal tunnel syndrome, cervical radiculopathy, cervical myelopathy, cubital tunnel syndrome, posterior interosseous nerve (PIN) syndrome.
• Sensory damage can also occur secondary to generalized neuropathies such as diabetes , hypothyroidism, heavy metal poisoning etc.³
• Nerve lacerations cause complete motor and sensory loss in the distribution of the cut nerve.

Instructions

1. Conduct a detailed patient history, including duration of symptoms, aggravating activities and past trauma
2. Evaluate the patient’s upper extremity for abnormal sensation (feeling) and/or dysesthesias
3. Check for numbness or decreased sensation in the affected areas and compare to unaffected areas.

Variations

• If cervical radiculopathy is suspected, also examine the patient’s neck and the affected shoulder.⁴

Related Signs and Tests

• Tinel sign
• Phalen’s sign
• Spurling test (for cervical radiculopathy)

• A positive (abnormal) result occurs when the patient experiences numbness or decreased sensation.

• A negative (normal) result occurs when the patient does not experience numbness or decreased sensation and has intact sensation.

• The most important sensory areas to test are the median nerve sensation, ulnar nerve sensation and to a lesser extent radial nerve sensation.
• When testing radial nerve function, the examiner should rely more on motor testing than sensory testing.
• Remember the most common monoradiculopathies involve C7 nerve root (long finger sensation), followed by C6 (thumb & index finger sensation).
• If PIN syndrome is suspected, lipomas should be considered, because they are the most commonly reported tumor to cause PIN syndrome.⁵
• Sensory deficiencies in compression neuropathies are usually partial not complete sensory loss.
• Complete nerve lacerations cause complete sensory and motor loss in the distribution of the cut nerve. In carpal tunnel syndrome the long finger typically demonstrates partial sensory loss as an early finding. 
• It is often important to simultaneously test a defintiely normal area of sensation like the opposite hand, forearm or even the face so that the patient can properly identify and distinguish the diffeence between normal sensation and mild to mederately decreased sensation (felling) in the area with questionable sensory nerve function.

1. Rayan G, Akelman E. The Hand: Anatomy, Examination and Diagnosis. Philadelphia: Lippincott Williams & Wilkins, 2011
2. Culp R, Jacoby S. Musculoskeletal Examination of the Elbow, Wrist and Hand: Making the Complex Simple. New Jersey: SLACK Incorporated, 2012
3. Doyle JR. Hand and Wrist. Philadelphia: Lippincott Williams & Wilkins, 2006.
4. Micev AJ, Ivy AD, Aggarwal SK, et al. Cervical Radiculopathy and Myelopathy: Presentations in the Hand. J Hand Surg Am2013;38(12):2478-81. PMID: 24054072
5. Dang A, Rodner C. Unusual Compression Neuropathies of the Forearm, Part I: Radial Nerve.  J Hand Surg Am 2009;34(10):1906-14. PMID: 19969199