Gastroesophageal Reflux Disease (GERD): The patient's symptoms of left upper abdominal pain radiating downwards, sharp shooting pain, nausea, and loose stools could be indicative of GERD, especially given the absence of fever, constipation, and blood in stool. The intermittent nature of the symptoms also aligns with GERD.

Irritable Bowel Syndrome (IBS): The combination of abdominal pain, loose stools, and nausea without blood or fever could suggest IBS, particularly if the patient experiences relief after bowel movements or if the symptoms are related to food intake.
Gastritis: Inflammation of the stomach lining could cause the described symptoms, including pain, nausea, and changes in bowel habits. The absence of fever does not rule out gastritis, as it can be caused by non-infectious factors.
Functional Dyspepsia: This condition involves recurring signs and symptoms of indigestion that have no obvious cause. Symptoms can include pain or discomfort in the upper abdomen, early satiety, and nausea, which align with the patient's presentation.

Pancreatitis: Although less likely given the absence of fever and severe pain, pancreatitis can present with abdominal pain radiating to the back and nausea. It's crucial to consider this diagnosis due to its potential severity and the need for prompt intervention.
Peptic Ulcer Disease: While the patient denies constipation and there's no blood in the stool, a peptic ulcer could still cause the described symptoms. The presence of a peptic ulcer is a significant concern due to the risk of perforation or bleeding.
Diverticulitis: Although typically presenting with left lower quadrant pain, diverticulitis can occasionally cause upper abdominal pain if the diverticula are located in the sigmoid colon near the splenic flexure. The absence of fever and blood in the stool does not entirely rule out this diagnosis.

Splenic Infarction or Rupture: These conditions could cause left upper quadrant pain but are less likely without a history of trauma or underlying conditions that predispose to splenic issues.
Gastric Cancer: Although rare in a 35-year-old male, gastric cancer can cause a variety of gastrointestinal symptoms, including pain, nausea, and changes in bowel habits. The absence of weight loss, anemia, or other systemic symptoms makes this less likely but not impossible.

Subjective: The patient is a 35-year-old male presenting with left upper abdominal pain that radiates downwards, described as sharp and shooting, accompanied by nausea and loose stools. Symptoms are intermittent, and the patient denies constipation, fever, and blood in the stool.
Objective: Physical examination and initial laboratory tests (e.g., complete blood count, electrolytes, liver function tests) are within normal limits.
Assessment: Based on the differential diagnosis, the most likely cause is GERD, with other considerations including IBS, gastritis, and functional dyspepsia. It's essential to rule out pancreatitis, peptic ulcer disease, and diverticulitis due to their potential severity.
Plan:
1. Initial Management: Start the patient on a proton pump inhibitor (PPI) for suspected GERD and recommend lifestyle modifications (e.g., dietary changes, weight loss if applicable, avoidance of late-night eating).
2. Diagnostic Tests: Order an upper endoscopy to evaluate for gastritis, peptic ulcers, or other mucosal abnormalities. Consider abdominal imaging (ultrasound or CT scan) if symptoms persist or worsen to rule out pancreatitis, diverticulitis, or other structural issues.
3. Follow-Up: Schedule a follow-up appointment in 2-4 weeks to reassess symptoms and adjust the treatment plan as necessary. If symptoms worsen or the patient experiences severe pain, vomiting, or signs of bleeding, they should seek immediate medical attention.