Signs and symptoms
Anal fistulae can present with the following symptoms:
skin maceration
pus, serous fluid and/or (rarely) feces discharge — can be bloody or purulent
pruritus ani — itching
depending on presence and severity of infection:pain
swelling
tenderness
fever
unpleasant odorThick discharge, which keeps the area wet

Diagnosis
Diagnosis is by examination, either in an outpatient setting or under anaesthesia (referred to as EUA or Examination Under Anaesthesia). The fistula may be explored by using a fistula probe (a narrow instrument). In this way, it may be possible to find both openings. The examination can be an anoscopy. Diagnosis may be aided by performing a fistulogram, proctoscopy and/or sigmoidoscopy. Possible findings:

The opening of the fistula onto the skin may be observed
The area may be painful on examination
There may be redness
An area of induration may be felt; thickening due to chronic infection
A discharge may be seen

Classification
Parks classification: This was done by Parks et al. from the UK in 1976, before MRI or endoanal ultrasound was available. It classified the fistula in four grades:
St James University Hospital Classification: This was done by Morris et al. in the year 2000. This classification was improvement over Parks classification as it was based on MRI studies. It classified the fistula in five grades. Garg classification: This was done by Pankaj Garg in 2017. This classification is improvement over both Parks and St James University Hospital Classification. This was based on MRI studies and operative findings in 440 patients. It classified the fistula in five grades. The grades of this classification correlate quite well with the severity of the disease.
Nezelof syndrome is an autosomal recessive congenital immunodeficiency condition due to underdevelopment of the thymus. The defect is a type of purine nucleoside phosphorylase deficiency with inactive phosphorylase, this results in an accumulation of deoxy-GTP which inhibits ribonucleotide reductase. Ribonucleotide reductase catalyzes the formation of deoxyribonucleotides from ribonucleotides, thus, DNA replication is inhibited. Symptoms and signs
This condition causes severe infections. it is characterized by elevated immunoglobulins that function poorly. Other symptoms are:
Bronchiectasis
Hepatosplenomegaly
Pyoderma
Emphysema
Diarrhea

Cause
Genetically speaking, Nezelof syndrome is autosomal recessive. the condition is thought to be a variation of severe combined immunodeficiency (SCID). However, the precise cause of Nezelof syndrome remains uncertain

Mechanism
In the mechanism of this condition, one first finds that the normal function of the thymus has it being important in T-cell development and release into the bodys blood circulation Hassals corpuscles absence in thymus(atrophy) has an effect on T-cells. Diagnosis
The diagnosis of Nezelof syndrome will indicate a deficiency of T-cells, additionally in ascertaining the condition the following is done:
Blood test (B-cells will be normal)
X-ray of thymus (atrophy present)

Differential diagnosis
The differential diagnosis for this condition consists of acquired immune deficiency syndrome and severe combined immunodeficiency syndrome

Treatment
In terms of treatment for individuals with Nezelof syndrome, which was first  characterized in 1964, includes the following(how effective bone marrow transplant is uncertain) :

Antimicrobial therapy
IV immunoglobulin
Bone marrow transplantation
Thymus transplantation
Thymus factors

See also
List of radiographic findings associated with cutaneous conditions

References
Further reading
Lavini, Corrado; Moran, Cesar A.; Uliano, Morandi; Schoenhuber, Rudolf (2009-05-08). Thymus Gland Pathology: Clinical, Diagnostic and Therapeutic Features. Springer Science & Business Media. ISBN 9788847008281. External links
PubMed