2025 – PAGE 382 – NEPHROLOGY

(DOUBLE TAKE) POSTSTREPTOCOCCAL GLOMERULONEPHRITIS (PSGN, AKA POST INFECTIOUS GLOMERULONEPHRITIS)

Poststreptococcal glomerulonephritis (PSGN, AKA post infectious glomerulonephritis) is a Group A Streptococcus (GAS) syndrome. Look for HEMATURIA + PROTEINURIA ± swelling ± HTN. There may be a history of a skin infection one month before, or a throat infection 1–2 weeks earlier. Labs will show a low C3 and NORMAL C4 ± renal impairment. Biopsy will show LUMPY BUMPY IgG deposits (biopsy is not required to make the diagnosis). Treat with IVF and a loop diuretic if there’s HTN. This generally has a GOOD prognosis, but you may consider steroids or cyclophosphamide for cases that are not improving. C3 should be followed until it’s back up to normal.

PEARL: Antibiotics given for a Group A Strep infection can prevent rheumatic fever, but they CANNOT prevent PSGN. Also, PSGN can occur from pharyngitis OR skin infections, but rheumatic fever only occurs after PHARYNGITIS.

PEARL: If the C3 level does not come back up to normal after 6 weeks, consider a different diagnosis, such as membranoproliferative glomerulonephritis (low C3 and normal C4) or lupus nephritis (+ANA, low C3 and C4). If the renal impairment is severe, obtain a biopsy to look for rapidly progressive glomerulonephritis (RPGN).

(DOUBLE TAKE) HEMOLYTIC UREMIC SYNDROME (HUS) AND THROMBOTIC THROMBOCYTOPENIC PURPURA (TTP)

Hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are two distinct disorders, but they are very similar disorders that can suddenly cause small thrombi throughout the body.

• Hemolytic Uremic Syndrome(HUS): There are 3 types of HUS that affect children. Shiga toxin-producing Escherichia coli (STEC) accounts for > 90% of cases and is the most commonly tested form of HUS. The STEC results in abdominal pain, vomiting and bloody diarrhea. Other forms of HUS include Pneumococcal-associated HUS in young children with pneumonia, and lastly complement-mediated HUS due to mutations in genes for complement proteins. These two are not likely to be tested. HUS symptoms may include fever, hemolytic anemia, thrombocytopenia, renal failure, and neurologic changes. Thrombi within the kidneys often cause renal dysfunction, so look for uremia, hematuria, oliguria, or an elevated creatinine. Thrombi in the skin may result in purpura or ecchymoses. Altered mentation, seizures, coma and hypertension may also occur. Hemolysis is caused by verotoxin and is Coombs negative. The complement levels are normal in STEC HUS. The bug may have been contracted from bad meat or milk ingestion.
• Thrombotic Thrombocytopenic Purpura (TTP): TTP may be associated with certain medications, pregnancy, or certain infections. In its most common form, antibodies develop which destroy the ADAMTS13 enzyme responsible for cleaving von Willebrand factor. An excess of VWF leads to an excess of clotting. A similar symptom profile to that of HUS may be present, including fever, hemolytic anemia, thrombocytopenia, renal failure, and neurologic changes. ADAMTS13 testing will show decreased activity.

PEARL: Although thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are often indistinguishable, some key differences may help. As the name suggests, hemolytic uremic syndrome is more likely to include renal failure. The classic triad of HUS includes Hemolytic anemia with schistocytes, Acute renal failure and Thrombocytopenia, so these findings will definitely be presented for any HUS case on the boards, but other findings of fever and neurologic changes may not. For TTP patients, thrombi are more likely to form in the brain (rather than the kidneys), so the neurologic symptoms are often much more severe in TTP patients (seizures, stroke, etc.) than HUS patients. TTP is also a disorder that tends to affect teens, whereas HUS tends to affect children under the age of five.

MNEMONIC: Thrombotic Thrombocytopenic Purpura (TTP) and Hemolytic Uremic Syndrome (HUS) can be recalled by using the mnemonic FAT RN. Fever, Anemia, Thrombocytopenia, Renal Failure, and Neurologic Symptoms.

MNEMONIC: The mnemonic which encompasses the classic triad for HUS is simply HAT (Hemolytic anemia, Acute renal failure, and Thrombocytopenia).

MNEMONIC: TTP occurs in adolescents and more commonly results in severe neurological symptoms than those of HUS. TTP = Teen = Top of head.