Prognostication in cervical spondylotic myelopathy: Proposal for a new simple practical scoring system.

CONTEXT: The ability to preoperatively predict the outcome in cervical spondylotic myelopathy (CSM) helps in planning management and counseling the patient and family. AIMS: A simple prognostic scale, namely, the Madras Institute of Neurology Prognostic Scale (MINPS) for CSM has been proposed. SETTINGS AND
DESIGN: Six well-known prognostic factors, namely, age, duration of symptoms, neurological disability (Nurick's grade), number of levels of compression, effective canal diameter, and intrinsic cord changes, have been taken into account. Each factor has been divided into three subgroups and allotted a score. The total score in this scale ranges from a maximum of 18 to a minimum of 6.
MATERIALS AND METHODS: This scale has been evaluated in a group of 85 patients operated for CSM. STATISTICAL ANALYSIS USED: The usefulness of MINPS was statistically assessed using ANOVA test.
RESULTS: It has been found that majority of patients with a score of 14 or more improved; those with a score of 9 or less deteriorated; those with a score between 10 and 13 remained static.
CONCLUSIONS: The MINPS for CSM is a very practical scale which can be applied easily with the available clinical and radiological data, with good accuracy of outcome prediction. This is the first scale of its kind.

Introduction

Cervical spondylosis is a common problem affecting the elderly population. It occurs in about 90% of men above 50 years and women above 60 years.[1] Myelopathy is a serious sequelae of spondylosis, occurring in about 5-10% of these patients.[2] Majority require surgical management.

The outcome following surgery is variable.[34567] The ability to predict the outcome preoperatively will help the surgeon to identify patients with good outcome and also to plan proper rehabilitation for poor outcome groups. It also helps in counseling the patient and his family and to prepare them better for postoperative rehabilitation. The prognostic factors for cervical spondylotic myelopathy (CSM) have been extensively evaluated.[89101112131415] At present, a few scoring systems are available only for assessing the functional grade of patients with CSM.[161718] But there is no comprehensive scoring system available to predict the prognosis. Hence, a new prognostic scale, the Madras Institute of Neurology Prognostic scale (MINPS) for CSM, has been proposed.

Materials and Methods

The Madras Institute of Neurology Prognostic Scale for cervical spondylotic myelopathy

This comprises six well-known prognostic factors, namely, age, duration of symptoms, neurological disability (Nurick's grade), effective canal diameter, number of levels of compression, and intrinsic cord changes as seen in T2-weighted magnetic resonance imaging (MRI). Each factor is further divided into three subgroups and each of these is given a score 1-3 depending on the expected outcome. The factor with the best prognosis is given 3 points, and the factor with the worst prognosis is given 1 point. The maximum total score of the scale is 18, while the minimum total score is 6. The details of the scale are given in Table 1.

Table 1

The MINPS for CSM

Evaluation of the Madras Institute of Neurology Prognostic Scale

The MINPS for CSM was applied on a group of patients to evaluate the scale. This was a retrospective study on 85 patients operated for CSM. The clinical and radiological findings were documented, and the required data were collected. The age of the patient, duration of symptoms, and functional grade according to Nurick's grade were recorded. The number of levels of compression, the effective canal diameter, and intrinsic cord changes in the T2-weighted image, were noted in the MRI scan of the cervical spine. The effective canal diameter was measured as the distance between the prominence of the posterior osteophyte to the nearest point on the spinolaminar line at the level of maximum compression. The intrinsic cord changes were recorded according to the classification of Chen et al.[8] They were divided into, either normal, type I changes or type II changes. The total score on the MINPS was calculated. The patients were followed-up postoperatively, and the outcome was noted according to the Nurick's grade. The outcome was recorded as improvement, static, or deterioration, depending on the comparative pre and postoperative Nurick's grade. The usefulness of MINPS was statistically assessed using ANOVA test, 17.5 version. The significance level was set at P < 0.05.

Results

The total number of patients in this study were 85. The period of follow-up ranged from 2 months to 2 years. The details of the MINPS and outcome in these patients are given in Table 2.

Table 2

The distribution of patients according to the MINPS and the outcome

The effect of individual factors on the outcome was also analyzed. The details of the distribution of individual factors and outcome are given in Table 3.

Table 3

The distribution of patients according to each factor in the scale and the outcome category

It was found that 81% of the patients with MINPS score of 14 or more had an improved outcome; 80% of the patients with MINPS score of 9 or less deteriorated; 59% of the patients with MINPS score between 10 and 13 were neurologically static.

Discussion

Outcome of surgery in CSM is variable. A number of prognostic factors in CSM has been studied and evaluated. Patient's age, duration of symptoms, preoperative neurological status, radiological findings including number of levels of compression, effective canal diameter, and intrinsic signal changes in the cord, have been found to be the most important of them.[89101112131415]

Age

Cervical spondylotic myelopathy is a disease of middle-aged and elderly. Age has been found to be an important prognostic factor in determining the outcome after surgery in CSM.[111519] Naderi et al. in a study of 27 patients with CSM found better neurological improvement in patients younger than 60 years.[19] Ahn et al. in their prospective study also found better outcome in patients less than 40 years of age.[15] In the MINPS, the age factor has been divided into three subgroups, namely, below 40 years, 40-60 years, and above 60 years. In the present study, 83% of patients under the age of 40 years showed improvement, whereas 96% of patients above the age of 60 either remained static or worsened.

Duration of symptoms

Long standing compression results in irreversible changes within the spinal cord. Hence, patients presenting with shorter duration of symptoms do better. This has been corroborated by various studies.[142021] Patients with duration of symptoms less than 1-year have been shown to have a better outcome than those with longer duration of symptoms. Hence, in the MINPS, the duration of symptoms factor has been divided into three subgroups, namely less than 1-year, 1-2 years and more than 2 years. In the present study, 75% of patients presenting with symptoms less than 1-year duration showed good improvement after surgery, whereas 78% of patients having duration of symptoms more than 2 years worsened or remained static.

Preoperative neurological status

Preoperative neurological status plays a very important role in determining the outcome after surgery. This has been corroborated by various studies. Holly et al. have shown that patients with lower Nurick's grade had a better outcome.[10] In MINPS, the pre-operative neurological status has been divided into three subgroups based on Nurick's grade, namely, 0-2, 3, 4-5. In the present study, 56% of patients with preoperative Nurick's grade 1 and 2 showed improvement; whereas, 92% of patients with grade 4 and 5 either remained static or worsened.

Effective canal diameter

Effective cervical canal diameter has been found to be a very important factor determining the outcome after surgery in CSM.[112223] The normal midsagittal diameter in the cervical spine C3 to C7 is 17-18 mm. Canal diameter < 10 mm is considered significant and is associated with varying neurological deficits. The effective canal diameter is measured from the prominence of the posterior osteophyte to the nearest point in the spino-laminar line. Ahn et al., White and Panjabi, Fager, and Fergusson noted that effective canal diameter is one of the important prognostic factors, and better prognosis is seen when the effective canal diameter is above 11 mm.[15232425] In the MINPS, the effective canal diameter factor is subdivided into three subgroups, namely, more than 11 mm, 9-11 mm and less than 9 mm. In the present study, 90% of patients with effective canal diameter more than 11 mm showed improvement; whereas 94% of patients with effective canal diameter 9 mm or less either worsened or remained static.

Number of levels of compression

CSM is commonly due to compression opposite C5-6 and C6-7 discs. This is due to accelerated osteophyte formation at the level of maximum movement during neck flexion and extension. The progress of the disease is, usually, contiguous and may be rostral or caudal. Fujiwara, Ahn have found that patients with one or two levels of cord compression had a better outcome than those with three or more levels of compression.[915] In MINPS, the factor of a number of levels of compression has been subdivided into 3 groups namely, single level, 2 levels and 3 or more levels. In the present study, 80% of patients with a single level of compression improved, whereas 93% with 3 or more levels of compression worsened or remained static.

Intrinsic cord changes

Intrinsic signal changes seen in T2-weighted MRI, reflects the pathological changes in the cord due to compression. Chen et al. studied MRI findings in 64 patients with CSM and classified intramedullary hyperintense signal changes in T2-weighted images into: Type I, where the hyperintense signal had a faint, fuzzy border and Type II, where the hyperintense signal had sharp well-defined border.[8] The Type I signal changes were indicative of edema and ischemia which are reversible, and Type II signal changes were indicative of myelomalacia which is irreversible. In the MINPS, the factor intramedullary signal changes has been subdivided into three groups, namely, no changes, Type I changes and Type II changes. In the present study, 60% of patients with no intramedullary signal change improved, whereas 92% with Type II signal change worsened or remained static.

All these prognostic factors have been extensively studied and found to be important in determining the outcome after surgery in CSM. But there is no comprehensive prognostic scale till today, which can objectively predict the outcome in advance. The MINPS has been devised to enable the physician to know the possible outcome after surgery and plan further rehabilitation. The MINPS is very simple, can be routinely applied with the minimum available clinical and radiological information and is readily reproducible. The MINPS has been found to correlate well with outcome: A score of 14 and above, 10-13 and 9 and less, are indicative of improvement, static outcome and deterioration, respectively. MINPS is likely to find wide acceptance and form part of the physician's armamentarium. We also plan to evaluate MINPS on a larger population, in multiple centers and also plan to undertake a prospective study to further validate this scale.