Differential Diagnosis for Acute Back Pain with Acute Foot Drop
Single Most Likely Diagnosis
- Lumbar Disc Herniation (L4-L5 or L5-S1): This is the most common cause of acute foot drop due to compression of the nerve roots, particularly L5, which controls the muscles responsible for foot dorsiflexion. The absence of incontinence or saddle anesthesia suggests a more localized nerve root compression rather than a central spinal cord or cauda equina lesion.
Other Likely Diagnoses
- Lumbar Spinal Stenosis: This condition can cause nerve root compression leading to foot drop, especially if there is a superimposed disc herniation or if the stenosis is severe enough to compromise the nerve roots.
- Trauma: Acute trauma to the spine can result in fractures or ligamentous injuries that compress or damage the nerve roots, leading to foot drop.
- Spinal Epidural Hematoma: Although less common, a hematoma in the spinal epidural space can compress the spinal cord or nerve roots, causing acute neurological deficits like foot drop.
Do Not Miss Diagnoses
- Cauda Equina Syndrome: Although the absence of incontinence or saddle anesthesia makes this less likely, any delay in diagnosis can lead to permanent neurological damage. It's crucial to maintain a high index of suspicion, especially if there are any "red flag" symptoms such as severe pain, progressive neurological deficits, or if the patient's condition worsens.
- Spinal Infection (Abscess or Osteomyelitis): Infections of the spine can cause rapid neurological deterioration due to compression of the spinal cord or nerve roots. Early diagnosis and treatment are critical to prevent long-term damage.
- Spinal Tumor: Both primary and metastatic tumors can compress the spinal cord or nerve roots, leading to acute neurological symptoms. The presence of systemic symptoms such as weight loss or a history of cancer would increase the suspicion for this diagnosis.
Rare Diagnoses
- Diabetic Amyotrophy: A condition associated with diabetes that can cause asymmetric muscle weakness, including foot drop, due to nerve root damage.
- Vasculitis (e.g., Giant Cell Arteritis): Inflammation of the blood vessels can lead to ischemia of the nerve roots, resulting in acute neurological deficits.
- Neurosyphilis: A rare cause of neurological symptoms, including foot drop, due to tertiary syphilis infection affecting the spinal cord or nerve roots.