Loin pain commonly originates from the kidney. Renal calculi are common and cause severe pain. However other sources of pain need to be considered.

Stones in the upper urinary tract can cause renal colic (said to be the most excruciating pain that a patient will experience).

Epidemiology

This will depend on the particular cause of the loin pain. Epidemiological factors worth bearing in mind are:

• The lifetime incidence of renal stones is about 12% for men and 4% for women with a peak age of 35 to 45.
  These rates are doubled with a positive family history.
• First presentation of renal stones in the elderly or children is uncommon (but should be considered).
• Renal stones are more prevalent in men than women and there is racial variation.¹
• Pyelonephritis and urinary infections are more common in women.
• Abdominal aortic aneurysms are common in elderly patients with risk factors.
• Back pain is very common in all age groups.

Assessment

History

• When did the pain start?
• Was the onset sudden or gradual?
• Is it continuous or intermittent?
• Describe the nature of the pain(for example stabbing, burning, gripping). Note the body language and use of hands.
• Is there nausea or vomiting?
• Are there aggravating or relieving factors? What is the effect of movement and deep inspiration?
• Is there any radiation of the pain?
• Are there any urinary symptoms? Does the urine look normal? (men notice their urine much more than women)
• Is there a history of pyrexia or even rigors?
• Has the patient had similar pain before?
• Always take a past medical, medication and brief family history.
• Ask about risk factors for those causes in the differential diagnosis (see below) where appropriate.

Examination

This may be adapted according to the history but should give particular consideration to:

• General appearance and observations:
  • Assess pyrexia, dyspnoea, shock.
  • Does the patient lie still (acute abdomen) or writhe around (colic)?
  • Note temperature, assess the pulse (rate and quality etc.) and BP.
• Respiratory system examination (see Respiratory System - History and Examination).
• Abdominal examination.
• Back examination.

Differential diagnosis

History and examination should have narrowed the differential diagnosis considerably.

Renal causes

• Renal colic:
  • Pain is sudden in onset, very severe and the patient often writhing around.
  • Pain may radiate to the groin and anteriorly.
  • Often there is tenderness over the renal angle.
  • Renal colic is rather more constant and persistent than biliary colic.
  • There is gross or microscopic haematuria in 85% (in the other 15%, absence of gross or microscopic haematuria does not exclude renal colic.)
  • A stone that is moving may be more painful than one that is static. Renal colic, or ureteric colic is described much more fully in its own article.
• Pyelonephritis:
  • The patient with pyelonephritis is ill, often with a very high temperature and even rigors.
  • There may be symptoms of urinary tract infection and often there is vomiting.
  • Pain is a dull ache.
  • Expect leukocytosis and pyuria. The presence of pyuria, fever, leukocytosis, or bacteriuria suggests the possibility of a urinary infection and the potential for an infected obstructed renal unit or pyonephrosis. Such a condition is potentially life threatening and should be treated as a surgical emergency.
• Blood clots can cause sudden ureteric obstruction and colic:
  • Causes include renal biopsy, or medical problems such as bleeding disorders, tumours of the kidney or renal pelvis, haemophilia, sickle cell disease, or glomerulonephritis.
  • An uncommon cause is the idiopathic loin pain haematuria syndrome² in which there is loin pain, haematuria of varying degree and no apparent cause.
• Papillary necrosis:
  • Acute obstruction of the ureter from the sloughed papilla occurs in papillary necrosis.
  • Women are affected more often than men.
  • Causes include analgesic abuse, cirrhosis, recurrent pyelonephritis, urinary tract obstruction, tuberculosis, sickle cell disease, renal transplant rejection, and diabetes.
• Kidney tumours:
  • The pain is gradual in onset and there may be painless haematuria and possibly a mass.
  • The commonest forms are clear cell carcinoma in adults and Wilm's tumour in children.
• PUJ (pelvi-ureteric junction) obstruction:
  • It usually follows drinking large amounts of fluid as the diuresis causes distension of the renal pelvis and colic.
• Renal infarction:
  • This is frequently misdiagnosed³ initially as acute renal colic, pyelonephritis, or acute abdomen.
  • Acute renal infarction affects both kidneys and both sexes equally.
  • The average age of affected patients is about 65.
  • Risk factors include age and risks for thromboembolism such as atrial fibrillation.
  • There is unilateral flank pain and haematuria.
  • Other common symptoms include fever, nausea, and vomiting. LDH and WBC are usually elevated.
  • Diagnosis is usually made by CT scan.
  • Treatment is with intravenous heparin and/or intra-arterial thrombolysis.

Other local causes

• Dissecting abdominal aortic aneurysms causes loin pain similar to renal colic in about 10% of cases.⁴ The aneurysm can be adjacent to the ureter and cause haematuria from irritation or trauma. Consider when an older patient presents with apparent renal colic for the first time.
• Consider the differential diagnosis of left upper quadrant pain or right upper quadrant pain.
• Herpes zoster causes a burning pain in a band corresponding to a dermatome. The pain may precede the rash. When the rash appears diagnosis is easy. The skin is tender.
• Muscular pain produces an aching discomfort that is exacerbated by lifting and bending. The affected area is likely to be tender. There may be a history of injury. Examination of the back should show the cause.
• Injury to the lower thoracic or upper lumbar nerve roots will cause radiculitis. Injury to the 10th, 11th, or 12th ribs has the distribution of renal colic but is usually sharp or stabbing. The pain is often acute and can radiate anteriorly and inferiorly, just like renal colic. Movement exacerbates the pain.
• Fracture of a transverse process in the thoracic or lumbar vertebrae can also produce this pain. Most patients are female. Radiculitis is a common cause of flank pain⁵ that is not of renal origin and should be suspected in patients with normal findings on urinalysis and normal findings on imaging studies of the urinary system. Fractured ribs may be produced by coughing.
• Retroperitoneal fibrosis produces pain that is dull and insidious in onset but becomes progressively more severe. There is fibrous overgrowth of the retroperitoneal organs from the midline. When it involves the ureters it causes hydronephrosis and even renal failure. It is usually idiopathic but it has been associated with the use of methysergide for migraine and some malignancies. Males are affected twice as often as females and patients are usually aged 40 to 60 years. Pain is usually located first in the lower flank and abdominal regions. Testicular and periumbilical pain develops later.

Pulmonary causes

A sharp stabbing pain can originate from the lung or pleura. The pain is typically pleuritic. Possible causes include:

• Tuberculosis
• Pneumonia
• Pulmonary embolism

Less common causes

• Crohn's disease
• Diverticulitis
• Appendicitis
• Myocardial infarction
• Renal vein thrombosis
• Glomerulonephritis
• Berger's disease
• Acute nephritis
• Polycystic kidney disease
• Cholecystitis
• Adrenal tumours (and haemorrhage)
• Colon cancer
• Splenic infarction

Investigations

• Urine examination:
  • Microscopy may show haematuria with stones, pyuria with infection and casts in disease of the kidneys. Gross or microscopic haematuria is present in about 85% of renal colic, so 15% will have neither microscopic nor macroscopic haematuria.
  • If urine pH <6.0 suspect a uric acid stone. If pH >8.0 infection with a urea-splitting organism such as Proteus spp., Pseudomonas spp. or Klebsiella spp is likely.
  • Urinary crystals of calcium oxalate, uric acid, or cystine may sometimes be found on urinalysis.
  • Mild leukocytosis often occurs in renal colic but WBC>15,000/ cu mm suggests infection, even if afebrile.
• Imaging:
  • KUB x-ray (kidneys, ureters, bladder) may show abnormal shadows of the renal tract. 70% of renal stones are radio-opaque. Phleboliths can be mistaken for stones.
  • Ultrasound is quick and easy and does not require radiation or contrast media. It shows stones if they are more than 0.5cm is diameter. It will indicate any hydronephrosis and the size and shape of the kidneys.
  • Helical CT can be very useful.⁶ Ureteric stones can be difficult to demonstrate by U/S and helical CT is the investigation of choice.⁷
  • IVP gives a clear outline of the entire urinary system and demonstrates even mild hydronephrosis.
    It can also show non-opaque stones as filling defects. Intravenous contrast material may provoke an allergic response or renal failure, and the need for multiple delayed films can take hours.
  • Retrograde pyelogram accurately shows the anatomy of the ureter and renal pelvis, as well as making a definitive diagnosis of any ureteric calculus. Any stone, even if radiolucent, becomes clearly visible, as well as any kinks in the ureter, strictures, or tortuosities that may be missed on other studies. Retrograde pyelograms can be safely performed in patients allergic to intravenous contrast media and in patients with renal failure because the contrast medium never enters the bloodstream.

Management

This depends upon the working diagnosis.

Oral fluids should be encouraged to facilitate the passage of stones and to reduce any risk of permanent damage to renal function. Many stones in the renal tract will pass spontaneously but large ones may require removal. Of ureteral stones, 95% of those 2 to 4 mm in diameter pass spontaneously but passage may take as long as 40 days. Intervention may be required in 50% of ureteral calculi greater than 5 mm. those larger than 7mm are unlikely to pass spontaneously. The degree of pain, and patient gender and age had no bearing on the time taken to pass a stone.⁸ Open surgery to remove stones is becoming less common as other techniques are employed.⁹

Obstruction with infection is often treated initially by percutaneous nephrostomy.