Kernig's sign: Excerpt from Signs & Symptoms

Kernig's sign: Excerpt from Signs & Symptoms: A 2-in-1 Reference for Nurses

A reliable early indicator and tool used to diagnose meningeal irritation, Kernig’s sign elicits resistance and hamstring muscle pain when the examiner attempts to extend the knee while the hip and knee are both flexed 90 degrees. However, when the patient’s thigh isn’t flexed on the abdomen, he’s usually able to completely extend his leg. (See Eliciting Kernig’s sign.) This sign is usually elicited in meningitis or subarachnoid hemorrhage. With these potentially life-threatening disorders, hamstring muscle resistance results from stretching the blood- or exudate-irritated meninges surrounding spinal nerve roots.
Kernig’s sign can also indicate a herniated disk or spinal tumor. With these disorders, sciatic pain results from disk or tumor pressure on spinal nerve roots.

History

If you elicit a positive Kernig’s sign and suspect life-threatening meningitis or subarachnoid hemorrhage, immediately prepare for emergency intervention. (See When Kernig’s sign signals CNS crisis, page 392.)
If you don’t suspect meningeal irritation, ask the patient if he feels back pain that radiates down one or both legs. Does he also feel leg numbness, tingling, or weakness? Ask about other signs and symptoms, and find out if he has a history of cancer or back injury.

Physical assessment

Perform a physical examination, concentrating on motor and sensory function. Assessing motor function includes inspecting the muscles and testing muscle tone and strength. Cerebellar testing is also done because the cerebellum plays a role in smooth muscle movements such as tics, tremors, or fasciculations. Sensory system evaluation involves checking the patient’s sensitivity to pain, light touch, vibration, position, and discrimination.

Medical causes

Lumbosacral herniated disk

A positive Kernig’s sign may be elicited in patients with a herniated disk, but the cardinal and earliest feature is sciatic pain on the affected side or on both sides. Associated findings include postural deformity (lumbar lordosis or scoliosis), paresthesia, hypoactive deep tendon reflexes in the involved leg, and dorsiflexor muscle weakness.

Meningitis

A positive Kernig’s sign usually occurs early with meningitis, along with fever and, possibly, chills. Other signs and symptoms of meningeal irritation include nuchal rigidity, hyperreflexia, Brudzinski’s sign, and opisthotonos. As intracranial pressure (ICP) increases, headache and vomiting may occur. In severe meningitis, the patient may experience stupor, coma, and seizures. Cranial nerve involvement may produce ocular palsies, facial weakness, deafness, and photophobia. An erythematous maculopapular rash may occur in viral meningitis; a purpuric rash may be seen in those with meningococcal meningitis.

Spinal cord tumor

Kernig’s sign can be elicited occasionally, but the earliest symptom of a spinal cord tumor is typically pain felt locally or along the spinal nerve, commonly in the leg. Associated findings include weakness or paralysis distal to the tumor, paresthesia, urine retention, urinary or fecal incontinence, and sexual dysfunction.

Subarachnoid hemorrhage

Kernig’s sign and Brudzinski’s sign can both be elicited within minutes after the initial bleed. The patient experiences a sudden onset of severe headache that begins in a localized area and then spreads, pupillary inequality, nuchal rigidity, and decreased level of consciousness. Photophobia, fever, nausea and vomiting, dizziness, and seizures are possible. Focal signs include hemiparesis or hemiplegia, aphasia, and sensory or visual disturbances. Increasing ICP may produce bradycardia, increased blood pressure, respiratory pattern change, and rapid progression to coma.

Special considerations

Prepare the patient for diagnostic tests, such as a computed tomography scan, magnetic resonance imaging, spinal X-ray, myelography, and lumbar puncture. Closely monitor his vital signs, ICP, and cardiopulmonary and neurologic status. Ensure bed rest, quiet, and minimal stress.
If the patient has a subarachnoid hemorrhage, darken the room and elevate the head of the bed at least 30 degrees to reduce ICP. If he has a herniated disk or spinal tumor, he may require pelvic traction.

Pediatric pointers

Kernig’s sign is considered ominous in children because of their greater potential for rapid deterioration.

Patient counseling

Teach the patient how to recognize signs and symptoms of meningitis as well as measures to prevent this infection. If the patient has a herniated disk, tell him to avoid activities such as lifting, sleeping prone, climbing stairs, and riding in a car. Show the patient how to apply a back brace or cervical collar, as needed, then have him give a return demonstration.