The sign of Kernig is a symptom that occurs in patients suffering from meningitis or subarachnoid hemorrhage. In these cases, the patient cannot extend the knees by having his thigh flexed at the hip, at a 90º angle.
This sign is named after the Russian neurologist Vladimir Mikhailovich Kernig (1840-1917), who documented this sign after observing it in several patients with meningitis. His research was published between 1882 and 1884.
Kernig's sign occurs because during meningitis, the meninges, which are the membranes that cover the central nervous system, surround the brain and spinal cord, become inflamed. This causes stiffness of the neck and neck muscles. Other symptoms related to the disease are photophobia and severe headache.
The ability to recognize the Kernig sign, together with other clinical signs representative of meningitis, achieving a quick and efficient evaluation by knowing the patient's history, is very useful to guide towards an adequate investigation and a specific treatment.
Clinical examination of Kernig's sign
To check for the presence of Kernig's sign, patients should be in the supine position. In this position, the person can easily extend the leg.
In the case of sitting, or with the knees pressed to the chest, the extension of the knee only reaches 135 degrees and if it continues to press, it is very painful for the patient.
In addition to this discomfort, when trying to extend the leg the patient also feels pain in the lower back.
Causes
Inflammation of the meninges causes an irritating spasm in the hamstring muscles that extend the hip and bend the knee. The hamstring muscles are found attached to the pelvis and the tibia, playing a primary role in thigh extension and leg flexion.
The first hypotheses considered that the muscular hypertonia of the inner limbs of the body, together with the physiological predominance of the extensor muscles of the neck and back, over the flexor muscles of the lower limbs, were the explanation for the Kernig sign.
Later, it was discovered that the Kernig sign is a protective reaction to prevent pain or spasm of the hamstring muscles, which is induced by stretching of the inflamed and hypersensitive nerve roots.
This is why Kernig's sign asymmetries are also observed in patients. Irritation of the meninges also causes symptoms of hemiparesis, that is, weakness on one side of the body.
This is usually a very common secondary complication in cases of spinal cord injury or inflammation - such as meningitis.
Usefulness in clinical practice
According to the original article by the Polish pediatrician Josef Brudzinski (1874-1917) - who also described 4 maneuvers for the clinical diagnosis of meningitis- “Uber die kontralateralen Reflexe an den unteren Extremitatenbei Kindern”, “A New Sign in the Lower Extremities in Meningitis of Children ”; Kernig's sign was found in approximately 57% of meningitis cases.
Kernig's sign, along with Brudzinski's signs, is based on inflammation of the meninges and inflammation of the nerve roots. Therefore, greater inflammation increases the presence of these clinical signs, as occurs in the case of bacterial meningitis.
Another study carried out in 1991 by researchers Uchihara and Tsukagoshi, demonstrated a 9% susceptibility to Kernig's sign and 100% specificity in the diagnosis of inflammation of the meninges.
These signs, however, are more frequent in children and patients with moderate to severe inflammation, without showing greater severity of the disease.
In addition to this, Kernig's sign may be absent in infants or very elderly patients, as well as immunosuppressed or comatose patients. This should lead to the consideration of other methods of diagnosing meningitis in these types of people, since the fact that it is not present is not a cause to rule out meningitis.
However, due to its specificity, the Kernig sign, together with the Brudzinski sign, is often used in clinical practice and medical diagnosis as pathognomonic signs of meningitis.
Meningitis
Symptoms of meningitis.
Meningitis is a life-threatening disease if prompt and proper treatment is not obtained. Meningitis can be bacterial or viral.
Bacterial meningitis are more acute and can be fatal within hours. Viral meningitis in general are milder symptoms, caused mostly by enteroviruses or herpes viruses.
Being a serious disease, an early and accurate diagnosis is essential. This is why the Kernig sign, together with the Brudzinski sign, are important, since they allow to quickly and accurately detect the situation of a patient with meningitis.
Meningitis has been documented since ancient times. At the beginning of the 15th century BC Hippocrates taught that "If during an episode of fever, the axis of the neck suddenly twists and swallowing is difficult without a tumor, it is a fatal sign."
Meningitis as such was specifically described by the British physician Thomas Willis (1621-1675) and by the Italian anatomist and pathologist Battista Morgagini (1682-1771). The first documented epidemic of bacterial meningitis in the American continent was in 1806, where autopsies revealed the presence of pus between the brain membranes of the dura mater and pia mater, which validates the diagnosis.
This is the importance of the discovery of clear and specific signology of meningitis like Kenrig's. The Russian doctor first described the sign in 1882, at the Saint Petersburgh Mediznische Wochenschrift, where when examining seated patients, he discovered that he was not able to extend his knees without causing them pain.
To this day, even with all the technological advances, the medical community has not discovered other tests that replace these physical signs of meningitis.
A positive result of these signs is an indication to start antibiotic therapy, which increases the chances of a successful recovery from this disease that allows a return to a normal life.
Dr. Kernig's contribution will always be remembered as of utmost importance in the treatment of a disease with a high mortality rate such as meningitis.
References
- Kernig's sign of meningitis. Medical Encyclopedia. Medline Plus. Recovered from medlineplus.gov
- Mosby's Medical Dictionary. 9th edition. 2009. Elsevier.
- Collins Dictionary of Medicine. Robert M Youngson. 2004-2005.
- Appraisal of Kernig's and Brudzinski's sign in meningitis. Manmohan Mehndiratta, Rajeev Nayak, Hitesh Garg, Munish Kumar, and Sanjay Pandey. Annals of Indian Academy of Neurology. Oct-Dec 2012. Recovered from ncbi.nlm.nih.gov.
- Uchihara T, Tsukagoshi H. Jolt Accentuation of headache: the most sensitive sign of CSF pleocytosis. Headache. 1991. PubMed.
- Meningeal Signs: Kernig's Sign and Brudzinski's Sign, Series Editors and Contributing Authors: Asif Saberi MD and Saeed A. Syed MD, MRCP. Recovered from medical-dictionary.turner-white.com.