Chapter 7-1: Approach to the Patient with Low Back Pain - Case 1

CHIEF COMPLAINT

CONSTRUCTING A DIFFERENTIAL DIAGNOSIS

Most low back pain is caused by conditions that are troublesome but not progressive or life-threatening. The primary task when evaluating patients with low back pain is to identify those who have a serious cause of back pain that requires specific, and sometimes rapid, diagnosis and treatment. In practice, this means distinguishing serious back pain (pain due to a systemic or visceral disease or pain with significant neurologic symptoms or signs) from nonspecific back pain related to the musculoskeletal structures of the back, called mechanical back pain. The framework for the differential diagnosis reflects this task.

1. Back pain due to disorders of the musculoskeletal structures

   1. Nonspecific (mechanical) back pain: no definite relationship between anatomic abnormalities seen on imaging and symptoms

   2. Specific musculoskeletal back pain: clear relationship between anatomic abnormalities and symptoms

      1. Lumbar radiculopathy due to herniated disk, osteophyte, facet hypertrophy, or neuroforaminal narrowing

      2. Spinal stenosis

      3. Cauda equina syndrome

2. Back pain due to systemic disease affecting the spine

   1. Serious and emergent (requires specific and often rapid treatment)

      1. Neoplasia

         1. Plasma cell myeloma (formerly multiple myeloma), metastatic carcinoma, lymphoma, leukemia

         2. Spinal cord tumors, primary vertebral tumors

      2. Infection

         1. Osteomyelitis

         2. Septic diskitis

         3. Paraspinal abscess

         4. Epidural abscess

   2. Serious but nonemergent (requires specific treatment but not urgently)

      1. Osteoporotic compression fracture

      2. Inflammatory arthritis

         1. Axial spondyloarthritis

            1. With sacroiliitis on x-ray

            2. Without sacroiliitis on x-ray (with sacroiliitis on MRI or HLA-B27 positive plus clinical criteria)

         2. Peripheral spondyloarthritis

            1. With psoriasis

            2. With inflammatory bowel disease

            3. With preceding infection

            4. Without associated condition

3. Back pain due to visceral disease (serious, requires specific and rapid diagnosis and treatment)

   1. Retroperitoneal

      1. Aortic aneurysm

      2. Retroperitoneal adenopathy or mass

   2. Pelvic

      1. Prostatitis

      2. Endometriosis

      3. Pelvic inflammatory disease

   3. Renal

      1. Nephrolithiasis

      2. Pyelonephritis

      3. Perinephric abscess

   4. Gastrointestinal (GI)

      1. Pancreatitis

      2. Cholecystitis

      3. Penetrating ulcer

Figure 7-1 reorganizes the differential diagnosis using pivotal points and outlines the diagnostic approach to low back pain. In every patient with back pain, it is essential to systematically ask about and look for the clinical clues and pivotal points associated with serious causes of back pain (Table 7-1). In patients with positive findings, the initial patient-specific differential becomes limited to serious systemic causes of back pain or specific musculoskeletal back pain. Likelihood ratios (LRs) for these findings, when available, will be discussed later in the chapter. It is also essential to understand the clinical neuroanatomy of the lower extremity to properly examine patients with low back pain (Figures 7-2 and 7-3).