# Cryoglobulinemic Glomerulonephritis

## Overview & Classification

Cryoglobulinemia consists of circulating immune complexes that precipitate at temperatures \<37°C, causing systemic vasculitis.

| Type | % | Composition | Association | Renal Involvement |
|----|----|----|----|----|
| **Type I** | 10–15% | Monoclonal Ig (usually IgM) | Waldenstrom, CLL, myeloma | Rare (1–3%) |
| **Type II** | 50–60% | Monoclonal IgM-RF + polyclonal IgG | **HCV (80–90%)** | VERY COMMON (40–60%) |
| **Type III** | 25–30% | Polyclonal IgM-RF + polyclonal IgG | SLE, Sjögren, chronic infections | Less common (10–15%) |

**📚 Key Point:** Type II (mixed essential) cryoglobulinemia is the most common form causing significant kidney disease, and **HCV is the primary driver** globally. DAA therapy for HCV has revolutionized outcomes.

## Clinical Presentation: Classic Triad (50–60% of patients)

#### 1. Palpable Purpura

Lower extremities, buttocks. Triggered by cold exposure. Blanch incompletely. May progress to ulceration.

#### 2. Arthralgia/Arthritis

Large joints (knees, ankles, shoulders). Non-erosive. Intermittent or chronic.

#### 3. Renal Disease (GN)

Hematuria, proteinuria (\<3 g/day typical), hypertension, progressive renal dysfunction.

### Hallmark Laboratory Finding

**📚 Clinical Pearl:** **Low C4 (normal C3)** is a hallmark laboratory finding in cryoglobulinemic vasculitis. Combined with positive cryoglobulins + HCV serology + palpable purpura + GN, the diagnosis is clear. C4 may improve with treatment; follow organ findings and the underlying driver as well.

## Diagnosis

### Key Tests

- **Serum cryoglobulins (essential):** Must be collected in warm tube, transported at 37°C. Cryocrit \>5% indicates significant.
- **Complement:** C4 very low (often \<5 mg/dL); C3 normal. C1q low.
- **HCV serology/RNA:** Positive in 80–90% of Type II
- **Rheumatoid factor:** Positive (80–90%)
- **ANA, ANCA:** Usually negative

### Kidney Biopsy

- **LM:** Membranoproliferative pattern; **intraluminal thrombi** (PAS-positive hyaline deposits — pathognomonic)
- **IF:** Granular IgM, IgG + C3, C4, C1q deposition
- **EM:** Subendothelial deposits; may see intraluminal fibrillar or crystalline material

## Treatment

### HCV-Positive Cryoglobulinemia: DAAs First-Line

- **Sofosbuvir-based or glecaprevir/pibrentasvir:** Pan-genotypic, 12-week course, \>95% cure rate
- **Outcomes:** Viral eradication often improves vasculitis, but clinical and renal responses vary; persistence or relapse can occur despite sustained virologic response.
- Most patients do NOT need concurrent immunosuppression

### Severe Flares Requiring Acute Treatment

- **Plasmapheresis:** 1–1.5 plasma volumes daily for 5–10 sessions for RPGN, severe vasculitis
- **Corticosteroids:** IV methylprednisolone 500 mg–1 g daily x 3–5 days for acute flares
- **Rituximab:** 375 mg/m² weekly x 4; 70–80% response rate; depletes B cells producing IgM-RF
- **Cyclophosphamide:** Reserved for severe RPGN with crescents

**📚 Key Point:** DAA therapy for HCV has revolutionized cryoglobulinemia management. HCV eradication is the primary goal. Most patients do NOT need long-term immunosuppression once HCV is cured. C4 normalization serves as a marker of disease activity and treatment response.

## Prognosis

### DAA Era (Modern)

- **HCV eradication:** \>95% SVR with modern DAAs
- **Vasculitis remission:** Not guaranteed by viral clearance; follow clinical organ involvement as well as HCV RNA.
- **Renal outcomes:** Recovery depends on the severity and chronicity of injury. Persistent glomerulonephritis requires reassessment after antiviral treatment.

| Favorable               | Unfavorable                         |
|-------------------------|-------------------------------------|
| Low baseline creatinine | Baseline Cr \>2 mg/dL               |
| \<2 g/day proteinuria   | Nephrotic-range proteinuria         |
| No crescent formation   | Circumferential crescents           |
| Early DAA initiation    | Delayed treatment (established CKD) |

## Key Differential Diagnosis

| Feature           | Cryoglobulinemia   | Type II MPGN     | Lupus GN   | ANCA-RPGN |
|-------------------|--------------------|------------------|------------|-----------|
| **Cryoglobulins** | Positive           | Negative         | Negative   | Negative  |
| **C4 Level**      | Very low           | Normal or low C3 | Low C3, C4 | Normal    |
| **HCV**           | +80–90%            | Negative         | Negative   | Negative  |
| **Purpura**       | Palpable (typical) | Rare             | Rare       | Absent    |
| **DAA Response**  | Excellent          | N/A              | N/A        | N/A       |

## Clinical Pearls

1.  **Cryoglobulin testing supports diagnosis; false-negative results require attention to warm sample handling and repeat evaluation when suspicion remains high** — collected in warm tube at 37°C
2.  **Low C4 with normal C3 is characteristic pattern**
3.  **Palpable purpura + GN + HCV = cryoglobulinemia** until proven otherwise
4.  **DAAs are curative for HCV** (\>95% SVR); excellent first-line therapy
5.  **Cryoglobulinemia remission is slower than HCV eradication** — allow 6–12 months
6.  **Severe RPGN flares warrant plasmapheresis + rituximab** (not just DAAs)
7.  **C4 may improve with treatment; follow organ findings and the underlying driver as well**; use as marker of disease activity

## References

1.  Cacoub P, Comarmond C, Domont F, et al. Cryoglobulinemia Vasculitis. Am J Med. 2015;128(9):950-955. [PubMed](https://pubmed.ncbi.nlm.nih.gov/25837517/)
2.  De Vita S, Soldano F, Isola M, et al. Preliminary classification criteria for the cryoglobulinaemic vasculitis. Ann Rheum Dis. 2011;70(7):1183-90. [PubMed](https://pubmed.ncbi.nlm.nih.gov/21571735/)
3.  Comarmond C, Cacoub P, Saadoun D. Treatment of chronic hepatitis C-associated cryoglobulinemia vasculitis at the era of direct-acting antivirals. Ther Adv Gastroenterol. 2020;13:1756284820942617. [PubMed](https://pubmed.ncbi.nlm.nih.gov/32782479/)
4.  Zaja F, De Vita S, Mazzaro C, et al. Efficacy and safety of rituximab in type II mixed cryoglobulinemia. Blood. 2003;101(10):3827. [PubMed](https://pubmed.ncbi.nlm.nih.gov/12560225/)
5.  Terrier B, et al. Cryoglobulinemia vasculitis: an update. *Curr Opin Rheumatol*. 2013;25(1):10-18. [PubMed](https://pubmed.ncbi.nlm.nih.gov/23196322/)
6.  Terrier B, Cacoub P. Renal involvement in HCV-related vasculitis. Clin Res Hepatol Gastroenterol. 2013;37(4):334-9. [PubMed](https://pubmed.ncbi.nlm.nih.gov/23562337/)

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