Acute Flank Pain — Full Text

The โ€œflanksโ€ are those soft areas on our sides between the lower ribs & the top of the pelvic bone (tender meat for cannibals).  Pain that’s just in the flanks suggests kidney disease; our job is to separate out Kidney Infection from a Kidney Stone, even though most cases of flank pain wind up being simple Muscle Strains; there are also a few rare conditions.

Causes of Acute Flank Pain

xxxxxxxxxxxxCommon  
โ€ข Kidney Infection
โ€ข Kidney Stone
โ€ข Muscle Strain  
xxxxxxxxxxLess Common  
โ€ข Kidney Infarction
โ€ข Herpes Zoster (Shingles)
โ€ข Aortic Aneurysm (ruptured)

The symptoms of both acute Kidney Stone AND Kidney Infection (Pyelonephritis, or “Pyelo” for short) include broad ranges.  The patient with Infection may look weak, sweating, feverish, nauseated, and wincing as they clutch their side.  But a fair number may hardly seem sick, & others can feel anything in between.  The classic Kidney Stone patient paces restlessly, but most don’t.

When symptoms arenโ€™t classic for one or the other, we distinguish them in other ways:

  • Kidney Stone pain usually begins abruptly (when stone gets stuck), Infection more gradually.
  • Fever points to Infection, unless symptoms have continued long enough for a stone to become infected.
  • Wave-like episodes of pain, lasting around 20 minutes, that keep coming back, point to a Stone.
  • We also think Stone for pain that shoots down to groin or genitals.
  • Infection almost always causes flank or back tenderness (to pushing on it, or tapping); Stones are non-tender to touch, palpation, or tapping.
  • Past episodes of similar symptoms that get better on their own & recurred suggest Kidney Stones.
  • Both Infection and Stone may cause nausea or vomiting.

So we obtain a Urinalysis, looking more for negatives than positives.

  • Absence of “Leukocyte Esterase” on the rapid dipstick (or of White Blood Cells under the microscope) rules out Infection.
  • Absence of blood speaks against Stones (but not completely).
  • Presence of either could be either, or neither.
  • A  high pH (>7.0) suggests infection with the bacteria Klebsiella or Proteus, the latter of which can cause enormous permanent Stones.

Kidney Infarctions (when loss of blood supply kills some tissue) are rare.  We suspect them in patients at risk for throwing clots, such as those with Atrial Fibrillation or artificial heart valves.  Infarction can happen after trauma, and among people whose blood clots too easily (due to some uncommon diseases).  If such a patient has blood in the urine, or an unusually high blood pressure, we send them to an ER where they look for a high LDH (blood test) along with normal non-contrast CT scan (which would show no Stone).

There’s also the elusive Ruptured Aortic Aneurysm, often fatal; patients may complain of Flank Pain.  Weโ€™ll discuss this under Generalized Abdominal Pain.

Muscle Strain —ย  This winds up being our usual diagnosis, since the majority of patients with flank pain have normal Urinalyses.ย  We diagnose a strain if we can bring out the patient’s pain by palpating muscle, or by a specific movement of the torso, such as lateral bending or rotation.ย  Sometimes we test this against resistance, like pushing back when the patient tries a certain movement, & finding the pain is suddenly worse.ย  If we hear they’d been engaged in a new activity the day or two before, like sweeping leaves or tree climbing, we’re completely convinced.

Herpes Zoster (Shingles)  — This is the recurrence of Varicella virus; initial Varicella is called โ€œchickenpoxโ€.  Chickenpox lasts a week & goes away, but latent virus remains hidden in a nerve, and often reactivates many years later.  When it reactivates, it causes pain along the nerve pathway, & clusters of blisters which merge into crusts.

Zoster can occur on either side of the abdomen (upper, lower, or flan area).  Diagnosis may be tricky at first, if not impossible, since pain may precede skin lesions by 1-2 days.  Search the skin for even the tiniest splotches of redness or blisters, anywhere from spine to breast bone.  Donโ€™t freak out about the name; Zoster is just in the same family as the STD Herpes simplex (thereโ€™s no STD of the belly). If we diagnose Zoster for sure in a patient younger than 50, we suggest an HIV test.  Itโ€™ll probably be negative, but almost everyone with HIV gets Zoster at some point, due to even very subtle immune deficiency.  Not that you canโ€™t get HIV over 50, but age by itself is enough to cause Zoster reactivation.  When it comes to Zoster, 50 is โ€œelderlyโ€ (thatโ€™s when I began to get AARP mailings.  Hemlock & Neptune Societies too!!!).

See Acute Flank Pain for the clinicianโ€™s condensed thought-process when face-to-face with a patient.

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