Classifies the severity of strokes in the field.
Stroke is a leading cause of death and disability worldwide, necessitating rapid and accurate assessment to ensure timely intervention. The Los Angeles Motor Scale (LAMS) is a prehospital stroke severity assessment tool designed to facilitate the early identification and evaluation of stroke patients, particularly those with large vessel occlusion (LVO).
What is the Los Angeles Motor Scale (LAMS)?
The Los Angeles Motor Scale (LAMS) is a brief, three-item stroke severity assessment tool derived from the Los Angeles Prehospital Stroke Screen (LAPSS). It evaluates three key motor functions: facial droop, arm drift, and grip strength. Each item is scored on a scale of 0 to 2, resulting in a total score ranging from 0 to 5. A higher score indicates greater stroke severity and an increased likelihood of large vessel occlusion (LVO), a condition that requires urgent endovascular intervention.
The simplicity and efficiency of LAMS make it an ideal tool for use in prehospital settings, particularly by emergency medical services (EMS) personnel. Its design allows for rapid assessment, aiding in the decision-making process for patient transport to the appropriate facility, such as a Comprehensive Stroke Center (CSC) capable of performing endovascular procedures.
Structure of the LAMS
The LAMS evaluates three motor functions, each scored as follows:
- Facial Droop:
- Absent: 0 points
- Present: 1 point
- Arm Drift:
- Absent: 0 points
- Drifts down: 1 point
- Falls rapidly: 2 points
- Grip Strength:
- Normal: 0 points
- Weak grip: 1 point
- No grip: 2 points
The total score is calculated by summing the points from these three categories. A score of 4 or higher significantly increases the likelihood of LVO, with studies showing a seven-fold increase in risk.
Clinical Applications of LAMS in Stroke
1. Prehospital Stroke Assessment
The primary application of LAMS lies in the prehospital setting, where it is used by EMS personnel to assess stroke severity and predict the presence of LVO. Since LVO strokes are associated with higher morbidity and mortality, early identification is critical for determining the most appropriate transport destination. Patients with high LAMS scores (≥4) are often routed directly to CSCs, which are equipped to perform advanced interventions such as mechanical thrombectomy.
2. Predicting Functional Outcomes
LAMS has been shown to correlate well with long-term functional outcomes. Studies have demonstrated that higher LAMS scores at the time of assessment are associated with poorer outcomes, as measured by the modified Rankin Scale (mRS) at three months. For example, patients with a LAMS score of 4 or higher are more likely to have persistent large vessel occlusions and worse functional outcomes compared to those with lower scores.
3. Integration with Other Stroke Scales
LAMS complements other stroke scales, such as the National Institutes of Health Stroke Scale (NIHSS) and the LAPSS. While the NIHSS is considered the gold standard for comprehensive stroke assessment, it is time-consuming and impractical for prehospital use. LAMS, on the other hand, is faster and easier to administer, making it a valuable tool for initial stroke severity assessment. Studies have shown that LAMS correlates well with NIHSS scores, with a correlation coefficient of 0.75.
Advantages of LAMS
1. Simplicity and Speed
LAMS is a straightforward tool that can be administered quickly, often within a few minutes. This is particularly important in the prehospital setting, where time is of the essence in stroke management. Every 30-minute delay in treatment is associated with a 10% decrease in the likelihood of a good outcome.
2. High Sensitivity and Specificity
LAMS has demonstrated high sensitivity (81%) and specificity (89%) for identifying large vessel occlusions, making it a reliable tool for prehospital stroke assessment. Its overall accuracy is comparable to that of the NIHSS, with a c-statistic of 0.854.
3. Facilitates Appropriate Transport Decisions
By identifying patients with severe strokes or LVOs, LAMS helps EMS personnel make informed decisions about transport destinations. This ensures that patients receive the appropriate level of care without unnecessary delays, potentially improving outcomes.
Limitations of LAMS
1. Limited Scope
While LAMS is effective for assessing motor deficits, it does not evaluate other stroke symptoms, such as speech impairment or sensory deficits. This limits its ability to provide a comprehensive assessment of stroke severity.
2. Reduced Predictive Accuracy in Certain Settings
The predictive accuracy of LAMS is slightly lower when calculated in the prehospital setting compared to early post-arrival assessments. For example, the adjusted c-statistic for prehospital LAMS is 0.76, compared to 0.85 for early post-arrival LAMS.
3. Not a Substitute for Comprehensive Neurological Exams
LAMS is not intended to replace comprehensive neurological examinations or other diagnostic tools. It is a screening tool designed for rapid assessment and triage, and its findings must be confirmed through more detailed evaluations.
Comparative Performance of LAMS
Several studies have compared the performance of LAMS with other stroke scales, including the NIHSS and the Rapid Arterial oCclusion Evaluation (RACE) scale. Key findings include:
- Correlation with NIHSS: LAMS scores correlate strongly with NIHSS scores, indicating that it provides a reliable measure of stroke severity. A study found that LAMS had a c-statistic of 0.854 for identifying LVOs, compared to 0.933 for the NIHSS.
- Efficiency: LAMS is faster and easier to administer than the NIHSS, making it more suitable for prehospital use. It is also briefer than other LVO identification tools, such as the RACE scale, which evaluates five items.
- Outcome Prediction: LAMS predicts three-month functional outcomes with accuracy comparable to that of the NIHSS and the shortened NIHSS (sNIHSS). For example, the c-statistic for predicting three-month outcomes on the modified Rankin Scale was 0.75 for LAMS, 0.74 for NIHSS, and 0.69 for sNIHSS.
Conclusion
The Los Angeles Motor Scale (LAMS) is a valuable tool in the assessment and management of stroke, particularly in prehospital settings. Its simplicity, speed, and high predictive accuracy make it an essential instrument for EMS personnel, enabling them to identify severe strokes and large vessel occlusions quickly. By facilitating timely transport to appropriate facilities, LAMS plays a critical role in improving outcomes for stroke patients.
While LAMS has certain limitations, such as its narrow focus on motor deficits, its advantages far outweigh these drawbacks. When used in conjunction with other diagnostic tools and clinical judgment, LAMS can significantly enhance the efficiency and effectiveness of stroke care.
