OVERVIEW

What is interstitial nephritis?

Interstitial nephritis, also known as tubulointerstitial nephritis, is a general term for a group of diseases primarily characterized by histological and functional abnormalities of the renal tubulointerstitium.

Where is the renal interstitium located?

The renal interstitium refers to the area between renal blood vessels and renal tubules, composed of intrarenal blood vessels, nerves, and a small amount of connective tissue filling the spaces between urinary tubules.

The internal structure of the kidney can be divided into two parts: the renal parenchyma and the renal pelvis. The renal parenchyma consists of two layers: the outer cortex and the inner medulla. The renal interstitium is sparse in the cortical region but abundant in the inner medullary papilla. The main functions of the renal interstitium include providing structural support, facilitating osmotic diffusion, and producing small amounts of prostaglandins.

SYMPTOMS

What are the types of interstitial nephritis?

Interstitial nephritis can be divided into two main categories: acute and chronic:

• Acute interstitial nephritis: A group of acute kidney diseases characterized by inflammatory cell infiltration in the renal interstitium and tubular lesions. Based on etiology, it can be classified into drug-induced allergic, infection-related acute interstitial nephritis, and idiopathic acute interstitial nephritis of unknown cause. Clinically, drug-induced allergic acute interstitial nephritis is the most common.

• Chronic interstitial nephritis: A group of chronic kidney diseases characterized by renal interstitial fibrosis and tubular atrophy as the main pathological manifestations. Causes include drugs, heavy metals, radiation, etc.

What are the symptoms of interstitial nephritis?

• Acute interstitial nephritis:

  • Systemic allergic manifestations: Common symptoms include drug rash, drug fever, and peripheral eosinophilia. Joint pain or lymphadenopathy may also occur. However, systemic allergic reactions are often less obvious when caused by nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, acetaminophen, or indomethacin.

  • Abnormal urinalysis: Sterile leukocyturia, hematuria, and proteinuria may be present. The range of proteinuria varies widely, from negative to >1 g/day. In rare cases, nephrotic-range proteinuria (>3.5 g/day) may occur, often associated with NSAIDs. Occasionally, drugs like ampicillin, rifampin, interferon, and ranitidine have also been reported to cause massive proteinuria.

  • Renal dysfunction: Oliguric or non-oliguric acute kidney injury is common, often accompanied by tubular dysfunction, leading to renal glucosuria (glucose in urine), low specific gravity, and hypo-osmolar urine.

• Chronic interstitial nephritis:

  • The disease usually progresses slowly and insidiously, often first manifesting as tubular dysfunction. Distal tubular concentrating dysfunction leads to nocturia, low specific gravity, and hypo-osmolar urine, while proximal tubular reabsorption dysfunction causes renal glucosuria.
  • Early decline in creatinine clearance is followed by a gradual increase in serum creatinine until uremia develops.
  • Urinalysis shows mild changes, such as slight proteinuria and small amounts of red or white blood cells. As renal function deteriorates, kidney size decreases (unevenly in both kidneys), and anemia or hypertension may develop.

Is nephrotic syndrome common in interstitial nephritis patients?

Nephrotic syndrome is a clinical syndrome characterized by massive proteinuria (>3.5 g/day), hypoalbuminemia (<30 g/L), significant edema, and/or hyperlipidemia. It represents a severe renal lesion and is rare in interstitial nephritis patients.

Is renal failure common in interstitial nephritis patients?

Renal failure, in simple terms, refers to severe kidney damage and loss of function, leading to the accumulation of metabolic waste in the body. Acute kidney injury (formerly called acute renal failure) is not uncommon in interstitial nephritis patients, but most cases recover with prompt treatment, including dialysis. However, progression to chronic renal failure is rare.

Is uremia common in interstitial nephritis?

Chronic renal failure is a clinical syndrome caused by progressive and irreversible decline in kidney function due to various kidney diseases, eventually leading to complete loss of function. The end stage of chronic renal failure is commonly referred to as uremia, indicating the kidneys have lost their function. Since uremia represents the terminal stage of kidney disease, it is very rare in interstitial nephritis.

Why do some interstitial nephritis patients develop hypertension?

The kidneys play a key role in blood pressure regulation through hormonal and vascular mechanisms. When renal function is impaired, secondary hypertension may develop.

What complications can interstitial nephritis cause?

Main complications include nephrotic syndrome, renal tubular syndrome, and thromboembolic events in larger renal vessels or thrombotic microangiopathy in renal capillaries, leading to renal dysfunction, particularly renal failure.

CAUSES

What are the possible causes of interstitial nephritis?

Long-term use of painkillers such as aspirin, acetaminophen, and indomethacin can cause chronic interstitial nephritis. Those with infectious diseases, long-term exposure to heavy metals, or radiation are more susceptible.

Is interstitial nephritis contagious?

Interstitial nephritis is a histological and functional abnormality of the renal tubulointerstitium and is not contagious through any means. You can safely interact or live with others.

Is interstitial nephritis hereditary?

The onset of interstitial nephritis results from multiple factors, primarily drugs, infections, heavy metals, and radiation. It is not a genetic disease, so there is no need to worry.

DIAGNOSIS

How should interstitial nephritis be diagnosed?

• Acute interstitial nephritis: Recent medication history; manifestations of drug allergy; abnormal urinalysis; impaired renal tubular and glomerular function. Generally, the presence of the first two manifestations plus any one of the latter two is sufficient for a clinical diagnosis of acute interstitial nephritis. However, atypical cases (especially those caused by NSAIDs) often lack the second manifestation, requiring a definitive diagnosis through renal biopsy and pathological examination.

• Chronic interstitial nephritis: Highly suspected based on clinical manifestations, but pathological examination is often required for confirmation.

What diseases should interstitial nephritis be differentiated from?

Interstitial nephritis needs to be differentiated from glomerular diseases. The former may present with drug allergy manifestations such as fever, rash, eosinophilia, abnormal urinalysis, and impaired renal function (especially tubular damage), while the latter often has less obvious symptoms, possibly including hypertension, edema, and more severe renal dysfunction than interstitial nephritis. Differentiation can be made through renal pathological examination.

TREATMENT

How should interstitial nephritis be treated?

• Acute interstitial nephritis:

  • Discontinue the offending drug: Most mild cases resolve spontaneously after removing the allergen.

  • Immunosuppressive therapy: Severe cases may require glucocorticoids (e.g., prednisone 30–40 mg daily, tapered gradually after improvement, for a total of 2–3 months) to accelerate recovery. Cytotoxic drugs are rarely needed.

  • Dialysis: Patients with acute renal failure should undergo hemodialysis promptly.

• Chronic interstitial nephritis: Early cases require aggressive removal of causative factors. For chronic kidney dysfunction, conservative non-dialysis treatment is recommended to slow disease progression. If uremia develops, renal replacement therapy (dialysis or kidney transplantation) is necessary. Concurrent anemia and hypertension should also be managed.

Does interstitial nephritis require antibiotics?

Interstitial nephritis involves histological and functional abnormalities of the renal tubulointerstitium. While the term includes "nephritis," it is rarely caused by pathogen infections. Therefore, antibiotics are generally unnecessary.

When is hemodialysis needed for interstitial nephritis? What is hemodialysis?

Hemodialysis involves diverting blood outside the body to exchange waste and electrolytes with dialysate in a machine, purifying the blood before returning it. It helps maintain acid-base balance and remove excess fluid.

Dialysis is indicated for chronic kidney failure patients with unremitting uremic symptoms.

What medications are commonly used for interstitial nephritis?

• Immunosuppressants: e.g., prednisone, prednisolone.

• Anemia treatment: Iron supplements or blood transfusions for severe cases.

• Hypertension management: e.g., losartan, captopril, nifedipine.

What are the side effects of steroid therapy for interstitial nephritis?

Long-term high-dose steroids may cause:

Cushingoid features (e.g., moon face, central obesity), skin thinning, muscle weakness, hypokalemia, edema, hypertension, hyperglycemia, acne, infections, osteoporosis, peptic ulcers, growth suppression in children, and psychiatric symptoms. However, clinicians weigh benefits against risks and monitor complications.

Is treatment necessary for interstitial nephritis?

The kidneys are vital for filtering waste, regulating electrolytes, and maintaining homeostasis. Untreated interstitial nephritis can lead to progressive renal failure or death.

Is surgery required for interstitial nephritis?

End-stage patients stable on long-term dialysis (≥1 year) may undergo kidney transplantation.

Do interstitial nephritis patients need hospitalization?

Early cases with mild symptoms can be managed outpatient. Advanced disease with significant renal damage requires hospitalization.

How long does treatment take, and is it expensive?

Treatment duration varies (weeks to months) based on severity, response, and complications. Costs depend on hospital resources, therapy choice, regional policies, and patient compliance. Early intervention is crucial.

Can interstitial nephritis be cured, and will it recur?

Early cases are curable and rarely relapse if the interstitium heals. However, triggers (e.g., drug allergies) may cause recurrence.

DIET & LIFESTYLE

How does interstitial nephritis affect daily life?

During the acute phase of interstitial nephritis, patients must rest more and receive active treatment. After the condition is controlled, they can fully participate in some manageable work, but only non-physical jobs. If the disease progresses to the uremia stage, regular hemodialysis will be required, which significantly impacts work and finances.

What dietary precautions should interstitial nephritis patients take?

During acute kidney injury, salt intake should be appropriately limited, with a light diet consisting of easily digestible, high-calorie, and high-quality protein foods.

Does interstitial nephritis affect fertility?

Patients with interstitial nephritis can have children, but pregnancy is generally not recommended during active treatment. Once the condition stabilizes and medication is discontinued, pregnancy can be planned under a doctor's guidance.

PREVENTION

Can Interstitial Nephritis Be Prevented?

Interstitial nephritis can be prevented by avoiding excessive fatigue and mental stress, guarding against bacterial or viral infections, actively preventing and treating infections, avoiding certain potentially triggering medications, maintaining a nutritious diet, and reducing exposure to heavy metals and radiation.