What could cause intermittent pain on the left side of the abdomen?

Intermittent left-sided abdominal pain can arise from a wide range of causes, spanning gastrointestinal, genitourinary, musculoskeletal, and gynecologic systems. The specific location—left upper quadrant (LUQ) versus left lower quadrant (LLQ)—and associated symptoms are critical for narrowing the differential diagnosis.

In the left upper quadrant, common etiologies include gastric or duodenal ulcers (especially if pain is burning, related to meals, or accompanied by nausea or hematemesis), splenic disorders (e.g., splenomegaly or infarction—often presenting with sharp, localized pain that may radiate to the left shoulder), and referred pain from cardiac conditions such as angina or myocardial infarction (particularly in atypical presentations where pain manifests in the LUQ rather than the classic substernal region). Pancreatic inflammation—though typically midline or right-sided—can occasionally cause left-sided radiation, especially in cases of tail-of-pancreas involvement.

In the left lower quadrant, diverticulitis is among the most frequent diagnoses in adults over 50, characterized by crampy or constant pain, often with fever, leukocytosis, and changes in bowel habits. Other possibilities include colonic neoplasms, infectious colitis (e.g., *Campylobacter* or *Shigella*), irritable bowel syndrome (IBS), or constipation-related distension. In women of childbearing age, gynecologic causes must be considered—including ovarian cysts (especially if ruptured or torsed), endometriosis, or ectopic pregnancy (a life-threatening emergency requiring immediate evaluation if there’s any possibility of pregnancy).

Less common but important considerations include left-sided kidney stones or pyelonephritis (often with flank tenderness, dysuria, or urinary urgency), abdominal wall strain or hernia (pain exacerbated by movement or palpation), and, rarely, aortic pathology such as an expanding abdominal aortic aneurysm—though this more commonly presents with midline or back pain, it may manifest atypically.

Red-flag symptoms warranting urgent medical evaluation include: fever >38.5°C, persistent vomiting, inability to pass stool or flatus, rectal bleeding, syncope or lightheadedness, signs of peritoneal irritation (e.g., rebound tenderness, guarding), or pain that is severe, sudden-onset, or progressively worsening. A thorough history—including onset, duration, character, aggravating/alleviating factors, and associated symptoms—as well as physical examination and targeted investigations (e.g., CBC, CRP, urinalysis, abdominal ultrasound, or CT imaging) are essential for accurate diagnosis and timely management.