Sensory Abnormalities

Department of the Navy
Bureau of Medicine and Surgery

Sensory abnormalities are extremely common, but they are often difficult to quantify and document due to their inherent subjective nature. Knowledge of the anatomy of the sensory half of the nervous system can help define the abnormalities and localize them. Our focus will be on differentiating emergencies from more routine problems by defining the process and sorting central versus peripheral, and above versus below the foramen magnum. We will discuss patterns of somatic sensory changes, and leave the special senses and radicular patterns of sensory loss to other chapters.

When gathering the history, elicit the exact nature of the abnormality by defining its characteristics, location, and time course. Frequently, motor weakness is translated into numbness and vice versa. Pain and paresthesias (tingling, prickling, limb falling asleep) along the course of a nerve are generally helpful in localizing the lesion to a peripheral nerve (from the nerve root outward). Central lesions can cause pain, but these tend to develop over weeks to months.

Sensory testing should include the following modalities

Primary Sensory

• Light touch - Use tissue, cotton ball, or finger

• Spinothalamic Tracts.

• Pinprick - Sharp non-cutting point.

• Temperature - Cold reflex hammer; warm water in a test tube.

Dorsal columns

• Joint position - Move the digit only 5-10 degrees.

• Vibration - 128 Hz tuning fork.

Secondary Sensory

• 2-point discrimination < 6 mm in fingertips.

• Graphesthesia - Write numbers on the palm.

• Stereognosis - Name coins.

• Double - Touch face and opposite hand to elicit extinction.

• Simultaneous.

• Stimulation.

Define the margins of the abnormal area by starting in the center and working towards the normal areas. Some helpful landmarks are included in this table:

The interpretation of the exam should generalize the findings in the following terms:

• hypesthesia (decreased sensation) versus anesthesia (absent sensation)

• above versus below the neck

• below a certain level

• proximal versus distal

• symmetric versus unilateral

• dermatomal, multiple dermatomal (either contiguous or not)

• root versus peripheral nerve

Pain and sensory loss in a single dermatome indicates peripheral injury (trauma, disc, overuse, and compression). Dissociated sensory loss (e.g., pain and temperature without vibration and position sense loss) indicates a central cord lesion such as syringomyelia or other intrinsic cord lesion. Pain and temperature loss on one side and vibration and position loss on the other suggests a Brown-Sequard syndrome of half the cord. Associated deficits in motor, cerebellar, bowel and bladder control, and reflex systems contribute to localization, and raise the urgency of the problem.

Syndromes correlated with sensory abnormalities

Certain syndromes commonly present with sensory abnormalities. Most of these are peripheral nerve injuries occurring at particularly vulnerable points along the course of the nerve.

In Bell's palsy, only the VIIth cranial nerve is affected but patients often complain about altered sensation in the same area. Marked trigeminal sensory loss and seventh nerve weakness should be investigated further as a cranial polyneuropathy.

Treatment options are limited to very selected cases. Emphasis should be placed on finding central lesions or well-delineated peripheral lesions. Bell's palsy generally resolves in several weeks in 90 percent of patients. Carpal-tunnel syndrome and other compressive neuropathies can be treated with a wrist extension splints and avoidance of repetitive motions. Surgery is usually reserved for associated weakness or other neurological signs.

1. Bowsher, David. Neurological Handbook for the Emergencies in Medical Practice: A Non-Specialist. London: Croom Helm, 1988.

2. Caplan, Louis R, and Kelly, John J. Consultation in Neurology. Toronto: B. C. Decker, Inc, 1988.

3. Demyer, William. Technique of the Neurological Examination. New York: McGraw-Hill Book Co., 1980.

4. Omer, George E. Physical Diagnosis of Peripheral Nerve Injuries, Ortho Clin North Am (Vol. 12., No. 2, April 1981).

Reviewed by CAPT J. F. Morales, MC, USN, Neurology Specialty Leader, Neurology Department, National Naval Medical Center, Bethesda, MD (1999).