What is the diagnosis and next steps for a 49-year-old female patient with sudden sharp lower back pain, primarily affecting both flanks but more severe on the left side, with significant limitation of range of motion, past medical history of hyperlipidemia managed with Rosuvastatin (rosuvastatin) and hyperthyroidism managed with Methimazole (methimazole), and worsening of pain with positional changes?

Diagnosis: Acute Mechanical Low Back Pain with Possible Vertebral Compression Fracture

Given this patient's sudden onset bilateral flank pain with severe range of motion limitation and midline tenderness, the primary concern is vertebral compression fracture, especially considering her age (49) and the acute presentation—plain radiography of the thoracolumbar spine should be obtained immediately as the first diagnostic step. 1, 2

Critical Red Flags Assessment

Immediately evaluate for the following emergent conditions:

• Cauda equina syndrome: Check for urinary retention (90% sensitivity), fecal incontinence, saddle anesthesia, and motor deficits at multiple levels 3, 1, 2

  • The patient's negative straight leg raise and absence of neurologic deficits make this less likely, but any new urinary symptoms require immediate MRI and neurosurgical consultation 3, 1

• Vertebral compression fracture: The bilateral flank pain with severe ROM limitation and pain on all movements strongly suggests this diagnosis 1, 2

  • Midline tenderness has a positive likelihood ratio of 14.7 for fracture in at-risk patients 2
  • Risk factors include age >50 years (approaching this threshold), history of osteoporosis, and steroid use 3, 1

• Spinal infection: Assess for fever, recent infection, or IV drug use 3, 1

  • No fever mentioned, but this should be explicitly checked

• Malignancy: History of cancer, unexplained weight loss, age >50 years, and failure to improve after 1 month are concerning 3, 1

Immediate Diagnostic Approach

Order plain radiography of the thoracolumbar spine now because:

• Clear acute onset with bilateral flank pain and severe ROM limitation warrants imaging despite being within 2 days of symptom onset 1, 2
• This differs from typical nonspecific low back pain where imaging can be deferred 4-6 weeks 3, 1
• Plain films are the appropriate initial study to evaluate for vertebral compression fracture 2, 4

If plain radiographs are negative but clinical suspicion remains high:

• Obtain MRI within 2-3 days, as initial negative radiographs do not rule out occult fractures 2
• MRI is superior to CT for visualizing soft tissue, vertebral marrow, and spinal canal without radiation 1, 5

Consider renal imaging only if:

• Severe flank pain persists or hematuria is present, then obtain CT abdomen/pelvis to evaluate kidneys 2
• However, musculoskeletal causes are far more likely given the bilateral nature and movement-related pain 2

Initial Management (While Awaiting Imaging)

Pharmacologic treatment:

• Start NSAIDs as first-line medication (ibuprofen 400-600mg TID or naproxen 500mg BID) 1, 2, 5
  • NSAIDs provide superior pain relief compared to acetaminophen for acute traumatic back pain with moderate-quality evidence 1, 2
  • Screen for cardiovascular and gastrointestinal risk factors before prescribing 5
  • Monitor for GI and renal toxicity 1
• Avoid opioids initially, as NSAIDs are equally effective with fewer adverse effects 1, 2
• Do not use systemic corticosteroids, as they have no benefit over placebo for low back pain 3, 1

Non-pharmacologic treatment:

• Modified activity, not bed rest 1, 2
  • Advise staying active within pain limits, as bed rest leads to deconditioning 1, 2
  • Avoid activities that worsen pain 1
• Apply superficial heat using heating pads for symptomatic relief 1

Consider skeletal muscle relaxants for short-term use if muscle spasm is prominent, though evidence is moderate 3, 5

Follow-Up Plan

If imaging reveals vertebral compression fracture:

• Refer to orthopedic spine surgery for evaluation 2
• Initiate osteoporosis workup (DEXA scan, vitamin D, calcium levels) 2
• Consider vertebroplasty or kyphoplasty consultation if pain is severe and refractory 2

If imaging is negative:

• Reevaluate within 48-72 hours if symptoms are not improving 2
• If pain persists or worsens over 2-3 days despite negative initial imaging, obtain MRI to evaluate for occult fracture 2
• If symptoms persist beyond 4-6 weeks without improvement, consider MRI if not already performed 1, 5

Immediate return precautions:

• New or worsening neurologic symptoms (motor weakness, sensory changes, bowel/bladder dysfunction) 1, 2
• Development of fever or constitutional symptoms 1
• Progressive pain despite appropriate analgesia 2

Common Pitfalls to Avoid

• Do not defer imaging in this case despite the short symptom duration—the acute onset, bilateral flank pain, and severe ROM limitation warrant immediate plain radiography 1, 2
• Do not prescribe prolonged bed rest, as it worsens outcomes 1, 2
• Do not start with opioids when NSAIDs are equally effective and safer 1, 2
• Do not miss cauda equina syndrome—specifically ask about urinary retention, which has 90% sensitivity 3, 1
• Do not assume normal initial radiographs rule out fracture—MRI may be needed if clinical suspicion remains high 2

Medication Considerations

Regarding her current medications:

• Rosuvastatin for hyperlipidemia is not associated with increased fracture risk and can be continued 6, 7
• Methimazole for hyperthyroidism should be continued, though hyperthyroidism itself can contribute to bone loss—ensure thyroid function is well-controlled 3