We are reporting the first documented case of intravascular large B-cell lymphoma (IVLBCL) manifesting in the endomysial and perimysial capillaries with its associated diagnostic dilemma. Our patient presented with progressive paraplegia. Initial laboratories were remarkable for hyponatremia, hypochloremia, lactic acidosis, elevated C-reactive protein, and lactate dehydrogenase. The bone marrow biopsy was unrevealing. However, a subsequent muscle biopsy confirmed the diagnosis of IVLBCL. As hyponatremia, endocrinopathies, connective tissue disease, rheumatological disorders, and occult cancer could all present similarly, our patient is a unique diagnostic dilemma. Randomized skin biopsy remains the best way to diagnose this disease, and rituximab-based chemotherapy with high-dose intrathecal methotrexate has proven to be a safe and effective regimen. With this initial evidence of IVLBCL involving the endomysial and perimysial capillary, we believe that muscle biopsy could be of value in diagnosing IVLBCL patients with neuromuscular symptoms.