Positive Findings (Patient Has This)
| Symptoms | Increased Disease Probability (Positive Likelihood Ratio) |
|---|---|
| No pain when seated | |
| Burning sensation around the buttocks, Intermittent priapism associated with walking, or both | |
| Urinary disturbance | |
| Improvement when bending forward | |
| Bilateral buttock or leg | |
| Neurogenic claudication | |
| Numbness of perineal region | |
| Improve when seated | |
| Exacerbation when standing up | |
| Bilateral plantar numbness | |
| Treatment for symptoms needs to be repeated every year | |
| Orthopedic disease | |
| Pain below buttocks | 1.4× (1.0-1.8) |
| Exacerbated while standing up | 1.2× (1.1-1.3) |
| Wake up to urinate at night | 1.2× (1.1-1.3) |
| Thigh | 1.1× (1.0-1.2) |
| Gluteal | 0.88× (0.79-0.98) |
| Signs on Physical Exam | Increased Disease Probability (Positive Likelihood Ratio) |
|---|---|
| Wide-based gait | |
| Abnormal Romberg test result | |
| Vibration deficit | |
| Pinprick deficit | |
| Age >65 (vs ≤65) | |
| Weakness | |
| Absent Achilles reflex | 2.1 (1.0-4.4) |
| No pain with flexion | 1.4 (1.0-2.0) |
| Symptoms worsened with bending forward | 0.48 (0.34-0.66) |
Negative Findings (Patient Doesn't Have This)
| Symptoms | Decreased Disease Probability (Negative Likelihood Ratio) |
|---|---|
| Neurogenic claudication | |
| Pain below buttocks | |
| Thigh | |
| Exacerbated while standing up | |
| Exacerbation when standing up | |
| Wake up to urinate at night | |
| Improvement when bending forward | 0.52× (0.46-0.60) |
| Bilateral buttock or leg | 0.54× (0.43-0.68) |
| No pain when seated | 0.57× (0.43-0.76) |
| Improve when seated | 0.58× (0.41-0.81) |
| Treatment for symptoms needs to be repeated every year | 0.75× (0.65-0.86) |
| Bilateral plantar numbness | 0.84× (0.76-0.92) |
| Urinary disturbance | 0.88× (0.83-0.93) |
| Orthopedic disease | 0.90× (0.83-0.98) |
| Burning sensation around the buttocks, Intermittent priapism associated with walking, or both | 0.95× (0.92-0.98) |
| Numbness of perineal region | 0.97× (0.94-1.0) |
| Gluteal | 3.3× (1.2-8.8) |
| Signs on Physical Exam | Decreased Disease Probability (Negative Likelihood Ratio) |
|---|---|
| Pain below buttocks | |
| Age >65 (vs ≤65) | |
| Thigh | |
| Exacerbated while standing up | |
| Exacerbation when standing up | |
| No pain with flexion | |
| Wake up to urinate at night | |
| Improvement when bending forward | 0.52 (0.46-0.60) |
| Bilateral buttock or leg | 0.54 (0.43-0.68) |
| Vibration deficit | 0.57 (0.40-0.82) |
| No pain when seated | 0.57 (0.43-0.76) |
| Improve when seated | 0.58 (0.41-0.81) |
| Wide-based gait | 0.60 (0.46-0.78) |
| Pinprick deficit | 0.66 (0.48-0.91) |
| Abnormal Romberg test result | 0.67 (0.51-0.87) |
| Weakness | 0.69 (0.49-0.96) |
| Absent Achilles reflex | 0.69 (0.49-0.96) |
| Treatment for symptoms needs to be repeated every year | 0.75 (0.65-0.86) |
| Bilateral plantar numbness | 0.84 (0.76-0.92) |
| Urinary disturbance | 0.88 (0.83-0.93) |
| Orthopedic disease | 0.90 (0.83-0.98) |
| Burning sensation around the buttocks, Intermittent priapism associated with walking, or both | 0.95 (0.92-0.98) |
| Numbness of perineal region | 0.97 (0.94-1.0) |
| Symptoms induced by having patients bend forward | 1.3 (1.2-1.5) |
| Gluteal | 3.3 (1.2-8.8) |
Narrative
Caveats
- A characteristic clinical presentation, including neurogenic claudication, radicular pain, or both; and
- Radiographic or anatomic LSS
Published/Updated
What are Likelihood Ratios?
LR, pretest probability and posttest (or posterior) probability are daunting terms that describe simple concepts that we all intuitively understand.
Let's start with pretest probability: that's just a fancy term for my initial impression, before we perform whatever test it is that we're going to use.
For example, a patient with prior stents comes in sweating and clutching his chest in agony, I have a pretty high suspicion that he's having an MI – let's say, 60%. That is my pretest probability.
He immediately gets an ECG (known here as the "test") showing an obvious STEMI.
Now, I know there are some STEMI mimics, so I'm not quite 100%, but based on my experience I'm 99.5% sure that he's having an MI right now. This is my posttest probability - the new impression I have that the patient has the disease after we did our test.
And likelihood ration? That's just the name for the statistical tool that converted the pretest probability to the posttest probability - it's just a mathematical description of the strength of that test.
Using an online calculator, that means the LR+ that got me from 60% to 99.5% is 145, which is about as high an LR you can get (and the actual LR for an emergency physician who thinks an ECG shows an obvious STEMI).
(Thank you to Seth Trueger, MD for this explanation!)