Interstitial nephritis is a renal condition resulting from a variety of causes such as immune-mediated injury, medications, infections, and other mechanisms. It is an important cause of renal failure.
No characteristic symptoms are apparent in both acute and chronic interstitial nephritis. However, a careful medical history may elicit conditions frequently associated with the disease. Hypertension is common in many cases of interstitial nephritis but some patients may have normal or even low blood pressure. Suspicion should be high in patients with connective tissue disorders or other conditions that require long-term treatment with NSAIDs or analgesics. Occupational history may also provide a clue as to whether the patient is chronically exposed to environmental toxins, and the family history may reveal the presence of genetic disorders that predispose to the condition.
A previous medical history positive for atopy or allergy with a recent intake of medications may be important diagnostic clues for acute allergic interstitial nephritis. However, the chronic form of this condition is often insidious, with patients remaining asymptomatic for a long period of time. Often, chronic tubulointerstitial disease is diagnosed incidentally during routine laboratory testing.
A form of interstitial nephritis with associated uveitis (tubulointerstitial nephritis with uveitis) may present with systemic symptoms of fever, weight loss, fatigue, or malaise. Myalgia, flank or abdominal pain, arthralgia, and polyuria or nocturia may also be present.
An elevated serum creatinine and the presence of white blood cells (WBC), WBC casts, or eosinophils in the urinalysis may suggest tubulointerstitial nephritis. These findings are generally different from other forms of acute kidney injury (AKI), such as red blood cells (RBC) and RBC casts in acute glomerulonephritis. Abnormal laboratory findings that appear shortly after intake of a new drug is suggestive of acute allergic tubulointerstitial disease, especially if the drug in question has been known to cause interstitial nephritis. However, the presence of normal urinalysis results does not exclude the diagnosis .
Imaging studies, namely ultrasound, should be done prior to biopsy and in order to rule out obstruction. A renal biopsy is performed to establish a definitive diagnosis, with typical histopathologic findings showing tubulointerstitial infiltrates composed of T lymphocytes and monocytes, with eosinophils, neutrophils, or plasma cells occasionally present. There is also marked interstitial edema, and inflammatory infiltration of the tubular basement membrane may be present. However, a renal biopsy may not be necessary in some cases, especially in patients whose renal function improves upon cessation of intake of offending agents.
The underlying etiology should be determined after a diagnosis of tubulointerstitial nephritis is made. This may involve several laboratory tests to rule out different etiologies associated with the condition. These tests may include autoimmune antibodies (ANCA, antinuclear antibody (ANA), anti-dsDNA, anti-Ro/SSA) to detect the presence of connective tissue disorders and vasculitides such as SLE, Sjogren's syndrome, or ANCA vasculitis, serological tests to identify viral, parasitic, or bacterial infections, and chest X-rays to rule out tuberculosis or sarcoidosis, among others.
The primary treatment of both acute and chronic interstitial nephritis relies on the proper management of the underlying cause, such as removal of the offending agent in acute allergic nephritis. Corticosteroids are useful for acute forms such as immune-mediated causes of interstitial nephritis and some cases of drug-induced interstitial nephritis. Patients with acid-base disorders, electrolyte imbalances, proteinuria, and renal insufficiency may require co-management with a nephrologist.
Prednisone 1mg/kg orally once daily with dose tapering spread over 4 to 6 weeks may be given for immune-mediated and drug-induced interstitial nephritis in order to hasten recovery and potentially decrease the need for dialysis. For the latter case, corticosteroids are most effective when given within two weeks of removal of the offending cause. However, NSAID-induced interstitial nephritis is less responsive to corticosteroids than drug-induced interstitial nephritis.
Corticosteroids should only be started after a definitive diagnosis is obtained through biopsy, and if no improvement occurs after a few days of removing the offending agent. Treatment with corticosteroids may produce variable results, with some patients recovering full renal function after a few weeks and some progressing to chronic renal insufficiency.
Management of chronic interstitial nephritis requires supportive measures such as controlling the hypertension and anemia related to the disorder. Angiotensin-converting enzyme (ACE)-inihibitors or angiotensin II receptor blockers (ARBs) may delay disease progression in patients with chronic interstitial nephritis and progressive renal injury. Patients may also benefit from dietary measures such as sodium restriction.
Patients with acute or chronic interstitial nephritis should receive follow-up care in order to monitor the renal function. Long-term follow up care is important for chronic interstitial nephritis in order to optimize control of blood pressure.
The most severe complication associated with tubuointerstitial nephritis is end-stage renal disease (ESRD), a condition that requires dialysis or renal transplantation. Acid-base disorders are often present due to the resultant renal tubular dysfunction. Patients with analgesic, Balkan endemic, or aristolochic acid nephropathies are at an increased risk for urothelial cancers.
Removal of the offending agent in allergic interstitial nephritis is sufficient for the resumption of normal renal function. Spontaneous improvement in renal function may occur after a microembolic event in cholesterol kidney disease, though complete resolution of the renal dysfunction is not expected to happen. Hypertension may be also be a factor in tubulointerstitial nephritis, though not all cases are associated with hypertension (acute allergic interstitial nephritis or Balkan endemic nephropathy).
In terms of disease progression, most cases of chronic tubulointerstitial nephritis eventually progress to ESRD, though at a much slower rate compared to glomerular disorders.
Many disease entities can cause injury to the renal interstitium and the renal tubules, as well as ingestion of substances harmful to the kidneys. Acute allergic interstitial nephritis is the most common form of interstitial nephritis and is caused by hypersensitivity reactions to certain drugs  . Nephrotoxic medications, which are drugs that directly cause renal damage, are a major cause of interstitial nephritis. Other significant substances that cause direct renal injury include toxins and heavy metal such as lead or mercury. Factors that cause acute cases of nephritis differ from those that cause the chronic form of the condition. Infections from different pathogens are a major cause of acute interstitial nephritis. These include viruses such as hantavirus, cytomegalovirus (CMV), and human immunodeficiency virus (HIV). Parasitic infections including toxoplasmosis or leishmaniasis and fungal infections such as histoplasmosis are also an important cause of acute interstitial nephritis. Bacterial infections, however, do not cause acute interstitial nephritis unless accompanied by urinary obstruction or reflux.
Chronic interstitial nephritis is a result of accumulated damage to the renal interstitium. Therefore, chronic exposure to heavy metals is an important cause of this condition, as well as long-term use of nephrotoxic drugs such as analgesics, tacrolimus, or cyclosporine. Cholesterol microembolism due to atherosclerotic ischemic renal disease can also cause chronic interstitial nephritis, as well as malignancies such as myelomas and leukemias. Disorders in metabolism that cause hyperoxaluria, hypercalcemia, or cystinosis lead to the development of this condition. Chronic interstitial nephritis may also be caused by a condition known as Balkan endemic nephropathy and exposure to aristolochic acid found in certain Chinese herbs .
Disorders that affect the immune system such as sarcoidosis, Wegener granulomatosis, systemic lupus erythematosus and antineutrophil cytoplasmic antibody (ANCA) vasculitis can cause both acute  and chronic forms of this disease.
Diseases that primarily affect the renal tubules and interstitium without involving the glomeruli (primary tubulointerstitial disease) account for 10-15% of all renal diseases worldwide and in the United States. This condition may even be more prevalent in Balkan countries where endemic nephropathy is common.
In terms of gender predilection, analgesic nephropathy is 5-6 times more common in women and is probably due to greater intake of these medications in this population. However, differences in analgesic metabolism or a higher sensitivity to analgesic toxic effects in females cannot be ruled out.
Although lead nephropathy may be more common in blacks due to environmental factors arising from socioeconomic status, tubulointerstitial nephritis does not demonstrate any racial predisposition.
The etiologies of tubulointerstitial nephritis may appear in different age groups. Atherosclerotic or ischemic kidney disease usually appear in the elderly population, whereas cystinosis, hyercalcemia, or oxalosis can appear in younger age groups. Renal injuries related to toxic agents such as lead may appear with advancing age since they are associated with the accumulation of the toxic substance.
The primary pathology in both forms of interstitial nephritis is due to inflammation affecting the renal interstitium and the renal tubular cells. This is caused by either lethal or sublethal injury that triggers the initial inflammatory response, which eventually lead to the release of inflammatory cytokines and infiltration of the renal interstitium and renal tubules by inflammatory cells. These events eventually result in either acute or chronic inflammation .
The acute form of interstitial nephritis has a greater chance of reversibility, even in cases of severe interstitial injury, as long as the damage does not extend to the epithelial basement membranes. The reason for this reversibility is most probably due to the regenerative capacity of the renal epithelium. On the other hand, chronic interstitial nephritis tends to be less reversible since it represents a chronic accumulation of injuries in the interstitium, leading to progressive renal insufficiency accompanied by tubular atrophy, fibrosis, and interstitial scarring.
Other pathological mechanisms can trigger the inflammation seen in interstitial nephritis. Acute tubulointerstitial nephritis is the result of an exaggerated immune response (hypersensitivity) against certain drugs, whereas bacterial or viral infections can cause direct damage to the renal interstitium. However, bacterial infections in the absence of significant urinary obstruction or reflux are not enough to cause interstitial injury since the renal parenchyma is generally resistant to damage in the absence of these conditions.
A thorough knowledge of the risk factors related to the development of interstitial nephritis is essential in the prevention of this condition. Careful monitoring of the clinical condition in patients at risk for interstitial nephritis and early intervention are equally important in preventing the development of this disease.
Many different forms of renal injuries may give rise to a condition called interstitial nephritis, characterized histologically by inflammation and edema of the renal interstitium accompanied by a sudden deterioration in renal function. Interstitial nephritis is a misnomer since this condition affects both the interstitium and the tubules of the kidney, and a more appropriate term would be tubulointerstitial nephritis. The characteristic renal histopathologic changes associated with this condition were first noted in 1898 during autopsies of patients with scarlet fever and diphtheria.
Interstitial nephritis may present as either an acute or chronic condition. The acute type is commonly caused by allergic drug reactions, whereas the chronic form of the disease is caused by a wide range of causes such as genetic diseases, disorders of metabolism, or obstruction in the urinary tract. Chronic exposure to heavy metals such as lead is also a causative agent, as well as ingestion of environmental toxins and certain herbs. Although a thorough medical history and urinalysis may suggest a diagnosis of interstitial nephritis, a biopsy is often required to form a definitive diagnosis. The prognosis and treatment of the condition varies, and will depend on the severity of the condition, the underlying etiology, and its potential reversibility  .
Interstitial nephritis is a disease causing inflammation (swelling) of the spaces between the kidney tubules. As a result, your kidneys will not be able to work properly. This disease may be temporary (acute) or long-lasting (chronic) and may even cause failure of the kidneys (renal failure) if not treated properly.
The following factors can cause interstitial nephritis:
Patients with interstitial nephritis may experience symptoms such as fever, rash, nausea, vomiting, decreased urine output, swelling in any area of the body, water retention and weight gain, and changes in the mental status such as drowsiness or confusion.
A physical examination from your doctor may reveal high blood pressure, fluid in the lungs, or abnormal heart or lung sounds. In addition, your doctor may request for laboratory tests such as complete blood count, urinalysis, arterial blood gas analysis, blood chemistry, blood urea nitrogen, or serum creatinine. Additional diagnostic tests such as a kidney ultrasound or a kidney biopsy may also be necessary.
Treatment of interstitial nephritis will depend on the cause of the disease. Stopping intake of medications that can cause this disease is often necessary, and dietary measures such as limiting salt and fluid intake may also help. Keeping your blood pressure low (if you have hypertension) is also an important part of the treatment. Dialysis may also be done if needed, though this is usually temporary.
Interstitial nephritis is usually a short-term disease and recovery is likely. Possible complications of interstitial nephritis include chronic renal failure if the damage to the kidneys is severe. Acid can also build up in the body if the kidneys cannot excrete it, causing metabolic acidosis.
Interstitial nephritis may be prevented through limiting the intake of drugs known to cause the condition.