Loin Pain

Loin pain refers to pain located in the flank region between the ribs and iliac crest, usually arising from the kidneys, ureters, or musculoskeletal system. It is a common presenting symptom in primary care and emergency medicine, requiring careful history, examination, and investigations to distinguish benign from life-threatening causes.

📖 Introduction & Pathophysiology

• The loin overlies the kidneys and retroperitoneal structures, making it a common site of pain in urinary tract disease.
• Pain arises from capsular stretch (renal inflammation, tumour, obstruction), smooth muscle spasm (ureteric colic), or irritation of parietal peritoneum/muscles.
• Referred pain: renal/ureteric pain often radiates to the groin, suprapubic area, or genitalia.
• Musculoskeletal and spinal causes must always be considered.

⚠️ Causes of Loin Pain

🩺 Clinical Assessment

• History: Onset, nature (colicky vs constant), radiation (loin → groin in renal colic), systemic symptoms (fever, weight loss, rigors).
• Red flags: Fever + rigors (urosepsis), haematuria, anuria, pulsatile abdominal mass (AAA), severe uncontrolled pain.
• Examination: Palpate for tenderness, masses, pulsatility. Check for costovertebral angle tenderness (pyelonephritis). Abdominal exam for peritonism or organomegaly.

🔎 Investigations

• Urinalysis: Haematuria, pyuria, nitrites.
• Blood tests: FBC, U&E, CRP, cultures, coagulation if intervention likely.
• Imaging: – CT KUB (non-contrast): Gold standard for renal colic. – Ultrasound: First-line in pregnancy, children, or if radiation contraindicated. Detects hydronephrosis, large stones, renal masses. – CT/MRI angiography: If vascular cause suspected.
• Special tests: Urine culture (infection), pregnancy test (ectopic pregnancy in women of childbearing age).

💊 Management

• Initial: Analgesia (NSAIDs first-line, opioids if severe), IV fluids, antiemetics. Catheterisation if obstructed and unable to pass urine.
• Renal colic: NSAIDs, tamsulosin (medical expulsive therapy for distal stones), urology referral if obstruction + infection, solitary kidney, or AKI.
• Pyelonephritis: IV antibiotics, fluids, admit if systemic symptoms.
• AAA: Emergency surgical referral if ruptured/symptomatic.
• Musculoskeletal: Simple analgesia, physiotherapy, reassurance.
• Gynaecological: Gynae referral for ectopic pregnancy, torsion, large ovarian cysts.

⚠️ Complications

• Urosepsis and septic shock.
• AKI from obstruction.
• Rupture of AAA → massive haemorrhage, death.
• Chronic kidney damage from recurrent stones or infections.

📚 Key Teaching Pearls

• Loin pain + haematuria = renal colic until proven otherwise.
• Loin pain + fever = pyelonephritis until proven otherwise.
• Always examine the abdomen for a pulsatile mass → exclude AAA.
• Consider gynaecological and musculoskeletal causes to avoid unnecessary urological interventions.

Cases - Loin Pain

• Case 1 (Renal colic – ureteric stone): 💎 A 42-year-old man presents with sudden, severe, colicky left loin-to-groin pain, associated with haematuria and nausea. He is restless and unable to find a comfortable position. CT KUB shows a 5 mm left mid-ureteric stone. Management: IV fluids, analgesia (diclofenac), tamsulosin for medical expulsive therapy. Outcome: Stone passes spontaneously within 2 weeks. Follow-up ultrasound confirms resolution.
• Case 2 (Pyelonephritis): 🔥 A 29-year-old woman presents with fever, rigors, right loin pain, and dysuria. Exam: right costo-vertebral angle tenderness. Urine dipstick: nitrites + leucocytes. Bloods: CRP 220, WCC 17. Management: IV fluids, IV cefuroxime, and analgesia. Blood and urine cultures sent. Outcome: Symptoms improve within 48 hours. Completed 10-day antibiotic course. Ultrasound excludes obstruction.
• Case 3 (AAA rupture presenting with loin pain): 🚨 A 70-year-old man with hypertension and smoking history presents with sudden severe left loin and back pain, hypotension (BP 80/40), and a pulsatile abdominal mass. Management: Emergency transfer to theatre. Resuscitated with permissive hypotension (maintaining SBP ~90), IV access, urgent vascular surgery. Open repair performed. Outcome: Survived surgery, transferred to ICU. Discharged home after 12 days with vascular follow-up.

🧑‍⚕️ Teaching Commentary

Loin pain is a red-flag symptom 🚩 that can range from benign to life-threatening. • Renal colic = colicky, radiating pain, haematuria, restlessness. • Pyelonephritis = constant pain + fever, systemic upset, CVA tenderness. • AAA rupture = severe pain with shock, pulsatile mass, immediate surgical emergency. 🔑 Always assess haemodynamic stability first, take a focused history (urinary, vascular, systemic), and use imaging (CT KUB, USS, CT angio) as appropriate.