Tubulo Interstitial Diseases Of The Kidney

Tubulo-interstitial diseases of the kidney is a heterogeneous group of disorders affecting the kidney that share similar features of both tubular and interstitial injury. Primary categories of this disease includes, acute and chronic interstitial nephritis.

Acute interstitial nephritis is an acute form of kidney injury characterized by an inflammation reaction in the interstitial tissues of kidney and presence of edema, which usually spares the glomeruli. The hallmark of interstitial nephritis is the infiltration of inflammatory cells into the interstitial compartment. Infiltrating cells are mainly T cells and monocytes, plasma cells and eosinophils. An acute inflammatory reaction is most commonly caused by a hypersensitivity reaction of a drug.

Other causes include

• Infections
• Idiopathic or immune mediated
• Medications that most commonly cause allergic reactions are antibiotics (Ampicillin, Oxacillin)
• Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)
• Proton pump inhibitors
• Bacteria implicated in causing this disease are Legionella, Brucella, Mycoplasma, Rickettsia, Leptospira and Chlamydia.
• There is a presence of swelling in between the kidney tubules.

Kidneys function to filter the circulating blood and remove toxins. Water and certain organic materials are re-absorbed from the filtered blood and unwanted products are released from the body via urine. Swelling of the tubules disrupts the normal filtration function of the kidneys. 

Symptoms 

• Most common symptom of interstitial nephritis is decreased urine output. It may increase in some cases. People can be symptomless in some cases. Other symptoms of interstitial nephritis include fever, presence of blood in urine, fatigue, mental confusion, nausea, vomiting, water retention and bloating sensation in the body.
• This disease does not have racial, age or gender predilection. It can affect anyone, of any age group. However, kidney toxicity depends on cumulative effects of toxic substances which means more the kidney is damaged due to toxic substances, the higher the risk of the kidney suffering from subsequent damage. With advancing age, the general functioning of the kidney is affected. This makes advanced age a risk factor for acute interstitial nephritis.

Clinical features

• Sudden decrement in the renal function is a typical presentation. It is most commonly seen in an asymptomatic patient or a patient who has been put on a new medication.
• It may occasionally present as renal failure.
• In the presence of an infection, a maculopapular rash, fever and eosinophilia are characteristically seen.
• Occurrence of skin rash >50 % of patients, fever > 75 % of patients and eosinophilia > 80% of patients.
• Pain in the lumbar and pelvic region.

Investigations:

• Presence of mild to moderate proteinuria
• Gross hematuria
• Sedimentation of red and white blood cells
• WBC casts, occasionally RBC casts are also present
• Increased serum creatinine levels
• Oliguria
• Confirmation of the diagnosis can be done by renal biopsy.

Treatment: Removal of the offending agents, discontinuation of the etiologic drug is the most important treatment modality. Complete recovery is inversely proportional to the duration of renal failure.
 

Chronic interstitial nephritis
The tubule cells undergo atrophy and there is a flattening of the epithelium. Basement membrane of tubules are frequently thickened. Cellular infiltrate is composed of lymphocytes, with only occasional neutrophils, plasma cells and eosinophils. There is a relative preservation of glomerular function until late in the disease, but an impairment of tubular functions like urine concentration, dilution, acidification and potassium excretion is seen early.