What is the diagnosis and treatment plan for a 59-year-old female presenting with lower abdominal pain, normal Computed Tomography (CT) scan of the abdomen and pelvis, and pending urinalysis and urine culture results, with consideration of Chronic Pelvic Pain Syndrome (CPPS) and potential treatment with muscle relaxants?

Differential Diagnosis for Lower Abdominal Pain in a 59-Year-Old Female

Single Most Likely Diagnosis

• Chronic Pelvic Pain Syndrome: This diagnosis is considered the most likely due to the normal CT scan and the discussion of all possible causes, including chronic pelvic syndrome. The patient's symptoms and the comprehensive approach to ruling out other causes point towards a chronic condition that may involve musculoskeletal, neurological, or psychological components.

Other Likely Diagnoses

• Urinary Tract Infection (UTI): Although urinalysis and urine culture were mentioned, the results are pending. A UTI could cause lower abdominal pain and would be a common and likely diagnosis if the cultures come back positive.
• Musculoskeletal Pain: Given the discussion about muscle relaxants, musculoskeletal pain is a plausible cause. This could be due to various factors, including strain or overuse of abdominal or pelvic muscles.
• Gastrointestinal Issues: Conditions like irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), or other gastrointestinal disorders could cause lower abdominal pain and might not be immediately apparent on a CT scan.

Do Not Miss Diagnoses

• Ovarian Cancer: Although less likely, ovarian cancer is a critical diagnosis not to miss, especially in postmenopausal women. It can present with non-specific symptoms, including abdominal pain.
• Diverticulitis: This condition involves inflammation of the diverticula in the digestive tract and can cause severe abdominal pain. It's essential to consider, especially if the CT scan was not definitive.
• Ectopic Pregnancy: Although less common in a 59-year-old, it's not impossible, especially if the patient is still menstruating. An ectopic pregnancy is a medical emergency.

Rare Diagnoses

• Endometriosis: While more common in younger women, endometriosis can occur at any age and might cause chronic pelvic pain.
• Interstitial Cystitis: A condition causing bladder pressure, bladder pain, and sometimes pelvic pain, which could be considered if other diagnoses are ruled out.
• Adhesions or Scar Tissue: From previous surgeries or infections, adhesions could cause bowel obstruction or chronic pain, although this might be less likely without a history of surgery or infection.