# Clinical Cases: Nephrolithiasis

## Case 1: Calcium Oxalate Stone with Acute Renal Colic

### Patient Presentation
**Demographics:** 38-year-old male

**Chief Complaint:** Sudden onset severe left flank pain for 6 hours

**History of Present Illness:**
The patient developed sudden severe left flank pain that woke him from sleep. The pain is colicky, radiating to the left groin and testicle. He has been nauseated with one episode of vomiting. He noticed pink-tinged urine. He has never had a kidney stone before but his father had multiple stones.

**Social History:**
- Low fluid intake (mainly coffee and soda)
- High protein diet
- No regular exercise (sedentary job)

**Physical Examination:**
- Blood pressure: 148/92 mmHg
- Heart rate: 98 bpm
- General: Writhing in pain, unable to find comfortable position
- Abdomen: Soft, mild left CVA tenderness
- GU: Normal external genitalia, mild left testicular tenderness (referred)

### Workup and Results

**Laboratory Studies:**
- Creatinine: 1.0 mg/dL
- BUN: 14 mg/dL
- Calcium: 9.6 mg/dL
- Uric acid: 7.2 mg/dL
- Urinalysis: 2+ blood, pH 6.0, no WBC, no bacteria

**CT Abdomen/Pelvis (Non-contrast):**
- 6 mm stone in left distal ureter at ureterovesical junction
- Mild left hydronephrosis
- No other stones
- Hounsfield units: 1,200 (consistent with calcium stone)

### Clinical Image

![Ureteral Stone CT](case_01_image.jpg)

*Non-contrast CT demonstrating a 6 mm calculus at the left ureterovesical junction (arrow) with associated proximal hydroureter and mild hydronephrosis.*

### Diagnosis
**Acute Renal Colic due to Calcium Oxalate Nephrolithiasis**

Supporting features:
- Classic colicky flank pain radiating to groin
- Hematuria
- High-density stone on CT (calcium)
- No infection

### Discussion
This case illustrates typical calcium stone presentation:

- **Most Common Stone Type**: The lecture notes that calcium oxalate stones account for 70-80% of all kidney stones, making this the classic presentation.

- **Renal Colic Characteristics**: The lecture describes colicky pain that radiates from flank to groin as the stone moves distally. Pain at the ureterovesical junction often radiates to the testicle/labia due to shared innervation.

- **CT is Gold Standard**: Non-contrast CT is the gold standard imaging modality with sensitivity >95%. Hounsfield units help determine stone composition - calcium stones typically >400 HU.

- **Stone Size and Passage**: The lecture states that stones <5 mm have >90% spontaneous passage rate, while 5-10 mm stones have ~50% passage rate. This 6 mm stone has reasonable chance of passage with conservative management.

### Treatment Plan
1. **Pain Control:**
   - NSAIDs first-line (ketorolac, ibuprofen)
   - Opioids for refractory pain
   - IV fluids for hydration

2. **Medical Expulsive Therapy:**
   - Tamsulosin 0.4 mg daily (alpha-blocker relaxes ureteral smooth muscle)
   - Expected passage within 4-6 weeks

3. **Follow-up:**
   - Strain urine to capture stone for analysis
   - Repeat imaging in 2-4 weeks if no passage
   - Urology referral if stone not passed by 4-6 weeks

4. **24-hour Urine Metabolic Evaluation:**
   - Perform 6-8 weeks after stone passage
   - Assess for hypercalciuria, hyperoxaluria, hypocitraturia

### Teaching Points
1. Non-contrast CT is the gold standard for kidney stone diagnosis
2. Stones <5 mm have >90% spontaneous passage rate
3. NSAIDs are first-line analgesia for renal colic
4. Alpha-blockers (tamsulosin) facilitate stone passage
5. Stone analysis guides prevention strategies

---

## Case 2: Uric Acid Nephrolithiasis

### Patient Presentation
**Demographics:** 54-year-old male

**Chief Complaint:** Recurrent kidney stones

**History of Present Illness:**
The patient has had 4 kidney stones in the past 3 years. His stones have been described as "hard to see on X-ray" and are usually treated conservatively. He has metabolic syndrome with obesity, type 2 diabetes, and hypertension. He reports low urine output and dark urine.

**Past Medical History:**
- Type 2 diabetes mellitus (HbA1c 8.2%)
- Obesity (BMI 34)
- Hypertension
- Gout (1 episode)

**Physical Examination:**
- Blood pressure: 142/88 mmHg
- BMI: 34
- General: Obese male
- Abdomen: Soft, non-tender

### Workup and Results

**Laboratory Studies:**
- Creatinine: 1.2 mg/dL
- Uric acid: 8.8 mg/dL (elevated)
- Fasting glucose: 156 mg/dL

**Urinalysis:**
- pH: 5.0 (acidic)
- Specific gravity: 1.028 (concentrated)

**24-hour Urine:**
- Volume: 1.2 L (low)
- pH: 5.2 (consistently acidic)
- Uric acid: 950 mg/day (elevated)
- Citrate: 220 mg/day (low)

**CT Scan:**
- 8 mm left renal pelvis stone
- Hounsfield units: 280 (radiolucent - uric acid)

### Clinical Image

![Uric Acid Stone](case_01_image.jpg)

*CT scan showing a uric acid stone in the renal pelvis. Uric acid stones are radiolucent on plain X-ray but visible on CT with lower Hounsfield units (typically <500 HU) compared to calcium stones.*

### Diagnosis
**Recurrent Uric Acid Nephrolithiasis with Metabolic Syndrome**

Key features:
- Radiolucent stones on plain X-ray (low HU on CT)
- Persistently acidic urine (pH <5.5)
- Metabolic syndrome with insulin resistance
- Hyperuricosuria

### Discussion
This case demonstrates uric acid stone pathophysiology:

- **Primary Risk Factor**: The lecture emphasizes that acidic urine (pH <5.5) is the primary risk factor for uric acid stone formation, even more important than hyperuricemia. Uric acid has a pKa of 5.5, meaning it is protonated and insoluble below this pH.

- **Metabolic Syndrome Connection**: The lecture describes how metabolic syndrome and insulin resistance impair renal ammoniagenesis, resulting in persistently acidic urine. This patient exemplifies this association.

- **Radiolucent Stones**: Uric acid stones are radiolucent on plain X-ray but visible on CT with lower Hounsfield units (<500 HU) compared to calcium stones.

- **Medical Dissolution**: Unlike calcium stones, uric acid stones can be dissolved by urinary alkalinization to pH 6.0-6.5.

### Treatment Plan
1. **Urinary Alkalinization (Primary Therapy):**
   - Potassium citrate 20 mEq three times daily
   - Target urine pH 6.0-6.5
   - Monitor pH with pH paper

2. **Increased Fluid Intake:**
   - Goal urine output >2.5 L/day
   - Low-sugar fluids preferred

3. **Dietary Modifications:**
   - Reduce animal protein intake (purine load)
   - Reduce fructose intake

4. **Consider Allopurinol:**
   - If hyperuricosuria persists despite alkalinization
   - Also addresses gout history

5. **Metabolic Syndrome Management:**
   - Weight loss
   - Glycemic control

### Teaching Points
1. Acidic urine (pH <5.5) is the primary risk factor for uric acid stones
2. Uric acid stones are radiolucent on X-ray but visible on CT
3. Metabolic syndrome impairs ammoniagenesis causing persistent low urine pH
4. Uric acid stones can be dissolved with urinary alkalinization (pH 6.0-6.5)
5. Target urine output >2.5 L/day for all stone formers

---

## Case 3: Struvite Staghorn Calculus

### Patient Presentation
**Demographics:** 62-year-old female with paraplegia

**Chief Complaint:** Recurrent urinary tract infections and malodorous urine

**History of Present Illness:**
The patient has T12 paraplegia from a motor vehicle accident 15 years ago and requires intermittent catheterization. She has had multiple UTIs over the years treated with antibiotics. She now presents with persistent foul-smelling urine, low-grade fevers, and flank discomfort despite recent antibiotic course.

**Past Medical History:**
- T12 paraplegia (wheelchair-bound)
- Neurogenic bladder requiring intermittent catheterization
- Recurrent UTIs (>5 per year)
- No prior kidney stones

**Physical Examination:**
- Blood pressure: 118/74 mmHg
- Temperature: 38.2C
- General: Wheelchair-bound, mild distress
- Abdomen: Right CVA tenderness
- GU: Clean intermittent catheterization site

### Workup and Results

**Laboratory Studies:**
- Creatinine: 1.4 mg/dL
- WBC: 14,200/mcL
- Urinalysis: Alkaline pH (8.0), numerous WBC, bacteria, ammonia odor
- Urine culture: Proteus mirabilis >100,000 CFU/mL

**CT Abdomen:**
- Large staghorn calculus filling right renal pelvis and extending into calyces
- Right kidney enlarged with cortical thinning

### Clinical Image

![Staghorn Calculus](case_01_image.jpg)

*CT scan demonstrating a staghorn calculus (struvite stone) filling the renal pelvis and branching into the calyces, resembling the antlers of a stag. These stones form in the setting of urease-producing bacterial infections.*

### Diagnosis
**Infected Struvite Staghorn Calculus with Proteus UTI**

Features:
- Staghorn morphology on CT
- Alkaline urine (pH 8.0)
- Urease-producing organism (Proteus mirabilis)
- Risk factors: neurogenic bladder, recurrent UTIs

### Discussion
This case illustrates struvite stone formation:

- **Urease Requirement**: The lecture states that struvite stones form exclusively in the presence of urease-producing bacteria. Urease hydrolyzes urea to ammonia, alkalinizing the urine and promoting struvite (magnesium ammonium phosphate) crystallization.

- **Common Urease Producers**: The lecture notes that Proteus species are the most common cause, followed by Klebsiella, Pseudomonas, and some Staphylococcus species. Notably, E. coli does NOT produce urease.

- **Staghorn Morphology**: Struvite stones grow rapidly in infected urine and fill the renal collecting system, creating the characteristic "staghorn" appearance.

- **Complete Removal Required**: The lecture emphasizes that complete surgical stone removal is essential - antibiotics alone will not cure the infection while stone material remains as a nidus.

### Treatment Plan
1. **Antibiotics:**
   - Culture-directed therapy
   - Initial broad-spectrum coverage, then narrow based on sensitivities

2. **Surgical Removal (Essential):**
   - Percutaneous nephrolithotomy (PCNL)
   - Complete stone removal required
   - May require multiple procedures

3. **Post-operative Care:**
   - Prolonged antibiotic course (4-6 weeks)
   - Repeat cultures to confirm sterilization

4. **Prevention:**
   - Optimize bladder management
   - Consider acetohydroxamic acid (urease inhibitor) if recurrent
   - Low threshold for UTI treatment

### Teaching Points
1. Struvite stones form only with urease-producing bacteria (Proteus, Klebsiella, Pseudomonas)
2. E. coli does NOT produce urease and does not cause struvite stones
3. Complete surgical removal is essential - antibiotics alone are insufficient
4. Staghorn calculi require PCNL for definitive management
5. Risk factors include neurogenic bladder, indwelling catheters, recurrent UTIs

---

## Image Reference

For visual reference of nephrolithiasis concepts, see:
- Radiopaedia: [Kidney stone disease](https://radiopaedia.org/articles/kidney-stone-disease) - Overview and imaging
- Wikimedia Commons: [Kidney stones](https://commons.wikimedia.org/wiki/Category:Kidney_stones) - Stone types
- Radiopaedia: [Staghorn calculus](https://radiopaedia.org/articles/staghorn-calculus) - CT findings

---

## Learning Points

1. **CT is Gold Standard**: Non-contrast CT >95% sensitive; Hounsfield units help determine composition

2. **Stone Passage Rates**: <5 mm = >90%; 5-10 mm = ~50%; >10 mm usually requires intervention

3. **Uric Acid Stone Key**: Acidic urine (pH <5.5) is primary risk factor; can dissolve with alkalinization

4. **Struvite = Infection Stones**: Require urease-producing bacteria; complete removal essential

5. **Prevention for All**: Fluid intake >2.5 L urine output daily; stone analysis guides specific interventions