Diagnostic Considerations
Meningeal carcinomatosis, also known as leptomeningeal disease, may cause subacute motor or sensory deficits to be present with low back or leg pain. In addition, patients with meningeal carcinomatosis often also have mental status changes, headaches, cranial nerve palsies, and/or nuchal rigidity. In cancer patients with thrombocytopenia, retroperitoneal bleeding can cause plexopathy, with a rapid onset of pain and neurologic signs that usually are developed fully in 24 hours. Other associated findings include flank, thigh, or low back ecchymoses. Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), which is felt to be immune mediated, can cause severe, symmetrical, peripheral neurologic deficits. Nerve root thickening may be noted in the lumbosacral plexus, a finding that may be associated with moderate gadolinium enhancement. [15, 16]
Causes of lumbosacral plexopathy not related to cancer include aortic aneurysms, diabetes mellitus (DM), obstetric procedures, trauma, and intragluteal injections. [17, 18] With aortic aneurysms, acute pain commonly is seen, and the resultant weakness typically worsens over 1-2 weeks and then stabilizes. A pulsatile rectal or abdominal mass also can be seen in many patients. Acute thigh pain with acute or insidious onset of weakness can result from diabetic amyotrophy and can be difficult to differentiate from the aortic aneurysms. Weakness with diabetic amyotrophy usually is noted proximally, with relative sparing of distal lower extremity muscles.
Differential Diagnoses
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Diabetic Lumbosacral Plexopathy
