How do you diagnose Polycystic Kidney Disease (PKD) in an elderly patient with numerous bilateral renal cysts, largest measuring 5.6 cm in the right kidney and 10.3 cm in the left kidney?

Diagnosing ADPKD in an Elderly Patient with Numerous Bilateral Renal Cysts

In an elderly patient with numerous bilateral renal cysts (largest 5.6 cm right, 10.3 cm left), the diagnosis of ADPKD can be established clinically using imaging criteria: for patients ≥60 years with positive family history, ≥4 cysts in each kidney confirms the diagnosis, while in those with unknown family history, >10 total cysts on MRI confirms ADPKD. 1

Diagnostic Algorithm

Step 1: Obtain Detailed Family History

• Perform a comprehensive three-generation family history specifically focusing on kidney disease, kidney failure, dialysis, transplantation, and known ADPKD in relatives 2
• Note that up to 50% of ADPKD cases may represent de novo mutations, so negative family history does not exclude the diagnosis 2
• If family history is positive, the diagnostic threshold is lower (≥4 cysts per kidney at age ≥60 years) 1

Step 2: Apply Age-Based Imaging Criteria

• For patients ≥60 years with positive family history: The presence of ≥4 cysts in each kidney on ultrasound confirms ADPKD 1
• For patients with unknown or negative family history: Kidney MRI should be performed, where >10 total cysts confirms the diagnosis 1
• Your patient's numerous bilateral cysts with large dominant cysts (5.6 cm and 10.3 cm) clearly exceeds these thresholds and strongly supports ADPKD 1

Step 3: Assess for Typical vs Atypical Presentation

• Typical ADPKD (Class 1): Bilateral and diffuse distribution with mild, moderate, or severe replacement of kidney tissue by cysts, where all cysts contribute similarly to total kidney volume 3
• Atypical ADPKD (Class 2): Includes lopsided presentation where ≤5 cysts account for ≥50% of total kidney volume 3
• Your patient's large dominant cysts (10.3 cm left, 5.6 cm right) may suggest a lopsided or atypical presentation, though the presence of "numerous" cysts suggests typical diffuse involvement 3

Step 4: Evaluate for Extrarenal Manifestations

• Screen for polycystic liver disease, which is present in >80% of ADPKD patients by age 30 years and increases with age 1
• Liver cysts are more common and severe in women 1
• Consider screening for intracranial aneurysms if indicated by family history or symptoms 3

Step 5: Consider Genetic Testing in Select Scenarios

• Genetic testing is particularly helpful when there are few kidney cysts, discordant imaging and kidney function, or negative family history 1
• In your elderly patient with numerous bilateral cysts, genetic testing is not required for diagnosis but may provide prognostic information 1
• PKD2 mutations result in milder disease with kidney failure typically in the 70s, making this genotype particularly relevant for elderly presentations 1
• If genetic testing is performed and identifies a pathogenic variant, use nomenclature such as ADPKD-PKD1 or ADPKD-PKD2 3

Differential Diagnosis Considerations

Rule Out Simple Cysts

• Simple renal cysts are extremely common in elderly patients (nearly one-third of patients ≥50 years) 4
• However, simple cysts are typically few in number, whereas your patient has "numerous" bilateral cysts 5
• The presence of very large cysts (10.3 cm) and numerous bilateral distribution strongly favors ADPKD over simple cysts 1, 5

Rule Out Acquired Cystic Disease (ACD)

• ACD occurs in patients with advanced chronic kidney disease or on dialysis 3
• Assess current kidney function (serum creatinine, eGFR) to determine if cysts could be acquired rather than genetic 3
• If kidney function is preserved despite large cyst burden, this favors ADPKD over ACD 3

Rule Out Isolated Polycystic Liver Disease (ADPLD)

• ADPLD (linked to PRKCSH, SEC63, GANAB genes) presents with no or few kidney cysts 3, 1
• Your patient's numerous bilateral renal cysts excludes isolated ADPLD 1

Rule Out Other Genetic Cystic Diseases

• Tuberous sclerosis complex, von Hippel-Lindau syndrome, and autosomal recessive PKD have distinct clinical features and typically present earlier in life 3, 5
• The bilateral diffuse cystic pattern in an elderly patient without other syndromic features strongly favors ADPKD 3

Prognostic Assessment

Mayo Imaging Classification

• For typical ADPKD (Class 1), calculate height-adjusted total kidney volume (htTKV) to classify disease severity into classes 1A through 1E 3
• Higher Mayo classes predict faster progression to kidney failure 3
• This classification has prognostic value only for typical ADPKD, not atypical presentations 3

Gene-Specific Prognosis

• PKD1 truncating variants: CKD stage 3 around age 40, kidney failure in 50s 3
• PKD2 variants: CKD stage 3 around age 55, kidney failure in 70s—more relevant for elderly presentations 3, 1
• Minor genes (IFT140, GANAB, DNAJB11): Generally milder phenotypes with kidney function often preserved into old age 3

Common Pitfalls to Avoid

• Do not dismiss the diagnosis based on lack of family history alone, as de novo mutations account for up to 50% of cases 2
• Do not require genetic testing for diagnosis when imaging criteria are clearly met 1
• Do not confuse simple age-related cysts with ADPKD—the key is the number and bilateral distribution of cysts 1, 5
• Do not overlook screening for liver cysts and other extrarenal manifestations, which are present in the majority of ADPKD patients 1