1. Infection
It is the most common complication of NS and also the main cause of death. Common sites of infection include respiratory tract, skin, urinary tract, and abdomen. The reasons for easy occurrence of infection are:
1Low humoral immunity;
2Abnormal cell-mediated immunity;
3Complement components, especially B factor and D factor affecting the alternative complement activation pathway, decrease and affect opsonization function;
4The loss of transferrin and zinc binding protein from the urine affects immune regulation and lymphocyte function;
5Protein malnutrition;
6Edema causes local circulatory disorders;
7Application of corticosteroids and immunosuppressive drugs.
2. Hypercoagulability and thrombotic and embolic complications
There is a hypercoagulable state in NS, the reasons are:
1The liver synthesizes more substances related to coagulation;
2Antithrombin III is lost from the urine;
3Plasma plasminogen activity decreases;
4Hyperlipidemia increases blood viscosity and strengthens platelet aggregation;
5Infection or vascular wall injury can activate the endogenous coagulation system;
6Long-term and large amounts of corticosteroids exacerbate hypercoagulability;
7Overuse of diuretics exacerbates blood concentration.
The main thromboembolic complications of NS are renal vein thrombosis, manifested as sudden flank pain, hematuria or worsening hematuria, oliguria, and even renal failure. In addition, when children have asymmetric swelling of both lower limbs, consider deep vein thrombosis of the lower extremities; when there are unexplained cough, hemoptysis, or dyspnea without positive pulmonary signs, be alert to pulmonary embolism; when there are sudden hemiplegia, facial palsy, and other neurological symptoms, consider cerebral embolism. The clinical symptoms of slow thrombosis are often not obvious.
3. Malnutrition
In addition to protein malnutrition and growth and development disorders, there are also low thyroid hormone levels, vitamin D deficiency, calcium and phosphorus metabolism disorders, etc.
4. Renal injury
1Acute renal failure
Possible causes include: antibiotics, diuretics, etc., causing tubular necrosis or acute interstitial nephritis; severe interstitial edema or proteinuria casts blocking the tubules; the formation of a large number of crescents on the original pathological basis; decreased blood volume leading to prerenal azotemia or combined with renal vein thrombosis.
2Tubular function damage
NS original underlying disease (such as focal segmental glomerulosclerosis) and large amounts of reabsorption and decomposition of urinary protein can cause tubular damage. Clinically, renal glycosuria, aminoaciduria can be seen, and severe cases present with Fanconi syndrome. These children have poor response to corticosteroid therapy and poor long-term prognosis.