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The precise neurological evaluation of patients with a depressed level of consciousness may present a challenge, even for experienced neurologists. Meningeal signs, particularly Kernig's sign and neck stiffness, are helpful in suggesting the diagnosis of meningeal irritation in intracranial infections, oedema or haemorrhage and belong to the limited number of physical signs examined in patients with coma or altered mental status. As long ago as 1907, the German–Russian physician Vladimir Kernig noticed an attenuation of his “Kernig's leg sign” on the paretic side in patients with meningeal irritation and concomitant hemiparesis.1 The American neurologist Thorner described in 1948 a modification of various meningeal signs on the paretic side.2 According to Thorner, Kernig's sign as well as the rarer Brudziński's sign can be both symmetric and asymmetric. In the case of asymmetric meningeal signs, hemiparesis on the side of less pronounced meningeal signs should be assumed. On the contrary, meningeal signs should always be symmetric in meningitis and subarachnoid haemorrhage without parenchymal involvement and paresis.2 Thorner pointed to an attenuation of meningeal signs on the paretic side as a very quick and easy method of diagnosing unilateral motor deficits.3 Diminution of Kernig's sign on the paretic side was explained by Thorner through disturbed transmission of a reflexive response to crural flexor muscles via the affected pyramidal tract.2
Both Kernig's hint in his historical publication and Thorner's subsequent study remained unknown and nowadays seem to be completely forgotten.
The aim of this study was to evaluate the diagnostic usefulness of an asymmetric Kernig's sign as an indicator of the presence of a hemiparesis in the clinical practice of critical care neurology.
We examined 51 consecutive patients with a positive Kernig's sign and depressed level of consciousness: cerebral infarction n=1; tumour n=1; meningoencephalitis n=5; cerebral haemorrhage n=14; and meningitis n=30. A CT or MRI scan was performed in all patients. Kernig's sign was examined bilaterally as follows: the hip and knee were flexed to a right angle and then an attempt was made to passively extend the knee. Kernig's sign was assessed as positive if complete knee extension was not possible because of tonic tension of the crural flexor muscles. A quantitative analysis of the so‐called “Kernig's angle” (the angle between the upper and lower leg measured with a protractor) was performed in each patient. We considered Kernig's sign as positive when the “Kernig's angle” was <180°.
Asymmetry of Kernig's sign was found in all patients (n=21) with meningeal irritation, who were found to have a concomitant hemiparesis or unilateral pyramidal signs, such as increased deep tendon reflexes, Babinski's sign, etc, and had corresponding cerebral lesions on CT/MRI (table 11).). There were eight women and 13 men, aged 20–90 years. The angle of Kernig's sign was in direct proportion to the degree of paresis: the more pronounced paresis, the larger Kernig's angle (ie, the less pronounced Kernig's sign). In eight patients with hemiplegia, Kernig's sign was completely absent on the plegic side. Kernig's sign was symmetric in all patients (n=30) with meningeal irritation without hemiparesis.
Kernig's sign is the most common and, apart from nuchal rigidity, the only quantifiable sign of meningeal irritation.3 Kernig's sign is sometimes interpreted as positive when the knee cannot be extended beyond 135°.4 We considered Kernig's sign as positive in accordance with the opinion of its inventor (ie, if ”Kernig's angle” was <180°).1 It is known that Kernig himself let patients sit upright in order to elicit the sign later named after him and interpreted the test as positive if this resulted in immediate insuperable knee flexion.1 Nevertheless, Kernig's original method was not used in this study, but the passive knee extension after initial hip and knee flexion to a right angle was carried out. This technique allows a more precise testing of Kernig's sign and is appropriated worldwide.4,5
The present study confirms the results of Thorner's forgotten paper from 1948.2 In addition to Thorner, who only noted attenuation of Kernig's sign by concomitant hemiparesis without performing any quantification, the quantitative evaluation of Kernig's sign was carried out in the present study. This revealed that the “Kernig's angle” was in direct proportion to the degree of paresis: the more pronounced the paresis, the larger Kernig's angle (ie, the less pronounced Kernig's sign). Moreover, the present study showed that a quantitative analysis of Kernig's sign may be quite a differentiated clinical test, which allows more detailed evaluation of motor deficits than the Glasgow Coma Scale or the FOUR score. For instance, in patient Nos 1, 11 and 14, who had unilateral pyramidal signs without clear evidence of paresis, Kernig's sign was slightly less prominent on the affected side than on the non‐affected side (135° vs 120°, 130° vs 120°, and 110° vs 100°, respectively) (table 11).). In patient Nos 3–6 with hemiplegia, Kernig's sign was diagnosed exclusively on the non‐paretic side, suggesting that a strictly unilateral Kernig's sign should point to a hemiplegia or a leg plegia. In patient Nos 2 (Medical Research Council (MRC) score 3) and 8 (MRC score 2) with pronounced paresis, Kernig's sign was only minimally positive on the paretic side showing an angle of 160° and 170°, respectively, which, according to Kernig, corresponded to a weak degree of contracture (>150°).1 We found no correlation between the degree of Kernig's sign and the level of consciousness, whereas patients with deep areflexic coma were not included in our study because of absent meningeal signs.
Although the clinical relevance of an asymmetric Kernig's sign is limited to patients with coma or altered mental status, in intracranial haemorrhage, meningoencephalitide, etc, its diagnostic value should not be underestimated. An asymmetric Kernig's sign is certainly of purely phenomenological interest in completely conscious patients with meningeal irritation and paresis because hemiparesis in these patients can be better scored on a motor scale such as the MRC score. However, unilateral attenuation of Kernig's sign can be applied in everyday clinical practice of critical care neurology as a reliable indicator of hemiparesis.
Competing interests: None.