Interstitial nephritis, also known as tubulointerstitial nephritis, is inflammation of the area of the kidney known as the interstitium, which consists of a collection of cells, extracellular matrix, and fluid surrounding the renal tubules.[1] In addition to providing a scaffolding support for the tubular architecture, the interstitium has been shown to participate in the fluid and electrolyte exchange as well as endocrine functions of the kidney.[1] There are a variety of known factors that can provoke the inflammatory process within the renal interstitium, including pharmacologic, environmental, infectious and systemic disease contributors. The spectrum of disease presentation can range from an acute process to a chronic condition with progressive tubular cell damage and renal dysfunction.

1. tubulointerstitial nephritis

2. INTRODUCTION
 Interstitial nephritis, also known as tubulointerstitial
nephritis, is inflammation of the area of the kidney known as
the interstitium, which consists of a collection of
cells, extracellular matrix, and fluid surrounding the renal
tubules.In addition to providing a scaffolding support for the
tubular architecture, the interstitium has been shown to
participate in the fluid and electrolyte exchange as well as
endocrine functions of the kidney. There are a variety of known
factors that can provoke the inflammatory process within the
renal interstitium, including pharmacologic, environmental,
infectious and systemic disease contributors. The spectrum of
disease presentation can range from an acute process to a chronic
condition with progressive tubular cell damage and renal
dysfunction.

3. SIGN AND SYMPTOMS
 Signs and symptoms
 Interstitial nephritis may present with a variety of signs and symptoms,
many of these nonspecific. Fever is the most common, occurring in 30-
50% of patients, particularly those with drug-induced interstitial
nephritis.Other general symptoms that occur with variable frequency
include nausea, vomiting, fatigue, lack of appetite, and weight loss.
More specific symptoms, such as flank pain, pain with urination, and
visible blood in the urine, as well as signs like hypertension can be
helpful in increasing suspicion for the diagnosis.The "classic" triad of
symptoms reported in early documented cases consisted of rash, joint
pain, and increased eosinophils in the blood; however, more recent
epidemiology suggests that this grouping of symptoms only occurs in a
small minority (5-10%) of patients. However, with modern drugs
causing between 70-90% of current cases, it is not surprising that the
earliest documented cases and a minority of today's may present
different symptoms.

5. CAUSES
 Common causes include infection, or reaction to
medication such as an analgesic or antibiotics such as
methicillin (meticillin). Reaction to medications
causes 71%. to 92% of cases.

9. Examples of Drugs Associated
With Interstitial Nephritis

10.  This disease is also caused by other diseases and toxins that
damage the kidney. Both acute and chronic tubulointerstitial
nephritis can be caused by a bacterial infection in the
kidneys known as pyelonephritis, but the most common
cause is by an adverse reaction to a medication. The
medications that are known to cause this sort of reaction
are β-lactam antibiotics such as penicillin and cephalexin,
and nonsteroidal anti-inflammatory drugs (aspirin less
frequently than others), as well as proton-pump
inhibitors, rifampicin, sulfa
medications, fluoroquinolones, diuretics, allopurinol, mesala
mine, and phenytoin. The time between exposure to the drug
and the development of acute tubulointerstitial nephritis can
be anywhere from 5 days to 5 months (fenoprofen-induced).

11. DIAGNOSIS
 At times, there are no symptoms of this disease, but when
they do occur they are widely varied and can occur rapidly or
gradually. When caused by an allergic reaction, the
symptoms of acute tubulointerstitial nephritis are fever (27%
of patients), rash (15% of patients), and enlarged kidneys.
Some people experience dysuria, and lower back pain. In
chronic tubulointerstitial nephritis the patient can
experience symptoms such as nausea, vomiting, fatigue, and
weight loss. Other conditions that may develop include
a high concentration of potassium in the blood, metabolic
acidosis, and kidney failure.

12.  Blood tests
 About 23% of patients have a high level of eosinophils in the blood.
 Urinary findings
 Urinary findings include:
 Eosinophiluria: Original studies with Methicillin-induced AIN
showed sensitivity of 67% and specificity of 83%.The sensitivity is higher
in patients with interstitial nephritis induced by methicillin or when the
Hansel's stain is used. However, a 2013 study showed that the sensitivity
and specificity of urine eosinophil testing are 35.6% and 68% respectively.
 Isosthenuria
 Blood in the urine and occasional RBC casts
 Sterile pyuria: white blood cells and no bacteria
 Nephrotic-range amount of protein in the urine may be seen with NSAID-
associated AIN

13.  Pathology
 While non-invasive patient evaluation (physical examination,
blood and urine testing, imaging studies) can be suggestive,
the only way to definitively diagnosis interstitial nephritis is
with a tissue diagnosis obtained by kidney biopsy. Pathologic
examination will reveal the presence of interstitial edema
and inflammatory infiltration with various while blood cells,
including neutrophils, eosinophils, and lymphocytes.
Generally, blood vessels and glomeruli are not affected.
Electron microscopy shows mitochondrial damage in the
tubular epithelial cells, vacuoles in the cytoplasm, and
enlarged endoplasmic reticulum.
 Gallium scan
 The sensitivity of an abnormal gallium scan has been
reported to range from 60% to 100%.

14. TREATMENT
 Corticosteroids have been a mainstay of therapy for
tubulointerstitial nephritis, but mycophenolate
mofetil may also have a role. Ultimately, however,
treatment depends on the underlying etiology.
 Treatment consists of addressing the cause, such as by
removing an offending drug. There is no clear evidence
that corticosteroids help. Nutrition therapy consists of
adequate fluid intake, which can require several liters
of extra fluid.