Differential Diagnosis for a 49-year-old Female with Urinary Frequency and Low Back Pain

Single Most Likely Diagnosis

• Musculoskeletal Low Back Pain: Given the patient's report of pain in the lower lumbar paraspinal musculature and the absence of signs of infection or CVA tenderness, musculoskeletal low back pain is the most likely diagnosis. This condition is common and can cause both low back pain and referred pain that might be interpreted as urinary frequency due to the proximity of the lumbar spine to the urinary system.

Other Likely Diagnoses

• Kidney Stones: Although the urinalysis does not indicate an infection, kidney stones could still be present and cause both low back pain (often radiating to the groin) and urinary frequency. The absence of infection does not rule out kidney stones.
• Overactive Bladder: This condition could explain the urinary frequency. While it might not directly cause low back pain, the two conditions could coexist, or the patient might be experiencing referred pain.
• Degenerative Disc Disease or Lumbar Spondylosis: These conditions can cause low back pain and, if severe, might lead to neurological symptoms. However, they are less likely to cause urinary frequency directly unless there is significant nerve root compression affecting the nerves that control bladder function.

Do Not Miss Diagnoses

• Spinal Epidural Abscess: Although less likely and not directly suggested by the current findings, a spinal epidural abscess is a serious condition that requires prompt diagnosis and treatment. It can present with back pain and, in rare cases, might cause urinary retention or frequency if it compresses the spinal cord.
• Cauda Equina Syndrome: This is a medical emergency that can present with low back pain, urinary retention or incontinence, and other neurological symptoms. Early diagnosis is crucial to prevent long-term damage.
• Ovarian Cancer: While rare, ovarian cancer can present with non-specific symptoms including low back pain and urinary frequency. It's essential to consider this in the differential, especially in post-menopausal women or those with risk factors.

Rare Diagnoses

• Tabes Dorsalis: A late manifestation of syphilis that can cause lightning pains, ataxia, and urinary incontinence. It's rare and usually associated with other neurological symptoms.
• Sacroiliitis: Inflammation of the sacroiliac joints, which can cause low back pain. It might be associated with urinary frequency if the inflammation affects nearby structures or if the patient has a related condition like Reiter's syndrome.

Given the patient's presentation, pending CBC and CMP results will help rule out systemic infections or metabolic disorders. Additional diagnostic studies to consider include:

• Imaging of the lumbar spine (e.g., MRI) to evaluate for musculoskeletal causes of back pain, degenerative changes, or more serious conditions like spinal epidural abscess or cauda equina syndrome.
• Renal ultrasound to check for kidney stones or other renal abnormalities.
• Urodynamic studies if overactive bladder is suspected and other treatments have failed.
• Further neurological examination and potentially an MRI of the spine if there's suspicion of a neurological cause for the symptoms.