**Question:** A 22-year-old man presents to the clinic complaining of low back pain and stiffness. The discomfort started several months ago as a mild dull ache in his back. The pain is more intense now, and it involves his back and hips. The symptoms seem worse at night and prevent him from sleeping. On physical examination, there is paravertebral muscle tenderness and limited flexion of the lumbar spine. Chest expansion as measured with a tape measure at the nipple line is also reduced. Figure below shows an x-ray of the lumbar spine. Which of the following is the most likely diagnosis?

A. Spinal stenosis
B. Muscle strain
C. Lumbar spondylolisthesis
D. Osteoporosis

**Answer:**

A. Spinal stenosis

**Core Concept:**

Spinal stenosis is a condition characterized by narrowing of the spinal canal, which can compress the spinal cord or nerve roots. This can lead to low back pain, radiating pain, and neurological deficits. In this case, the patient presents with low back pain, stiffness, and limited lumbar spine flexion.

**Why the Correct Answer is Right:**

The correct answer is spinal stenosis (option A) because:

1. The patient's symptoms started gradually and worsened over time, typically seen in degenerative conditions.
2. The radiating pain and neurological deficits are consistent with spinal cord or nerve root compression.
3. The reduced chest expansion (pleural space) indicates respiratory compromise, which is a potential complication of spinal stenosis.
4. The lumbar spine flexion limitation suggests spinal cord compression.

**Why Other Options Are Incorrect:**

Option B (muscle strain) is incorrect because:

1. The patient's symptoms are not acute and have developed over several months, not days.
2. Muscle strains usually present with acute onset and improve with rest and analgesics.

Option C (lumbar spondylolisthesis) is incorrect because:

1. Lumbar spondylolisthesis is an acquired condition typically caused by trauma or degenerative changes in the spine, which is not consistent with this patient's gradually worsening symptoms.
2. The patient's respiratory compromise and lumbar spine flexion limitation are not typical features of spondylolisthesis.

Option D (osteoporosis) is incorrect because:

1. Osteoporosis is an age-related condition affecting older individuals, not typically seen in a 22-year-old patient.
2. Osteoporosis is characterized by bone fragility and increased fracture risk, not spinal cord or nerve root compression.

**Clinical Pearls:**

1. Spinal stenosis can affect younger individuals due to congenital or developmental factors.
2. Spinal stenosis can present with respiratory compromise, as seen in this case.
3. The reduction in chest expansion and lumbar spine flexion limitation are clinical signs of spinal cord compression.