bubble_chart Overview

Allergic purpura falls under the category of allergic vasculitis and was first described by Schönlein and Henoch in the 1830s and 1870s, respectively. Hence, it is also known as Schönlein-Henoch vasculitis. This disease is the most common capillary hypersensitivity disorder, characterized by widespread small vessel inflammation as its pathological basis. Its main clinical manifestations include skin purpura, gastrointestinal mucosal bleeding, joint swelling, and nephritis. According to an analysis of 1,162 hospitalized cases at Beijing Children's Hospital from 1987 to 1991, the male-to-female ratio was 1.4:1. It predominantly affects older children, particularly those of school age, while infants under one year are rarely affected, with the youngest case being three months old. The incidence is higher in winter and spring and lower in summer.

bubble_chart Etiology

Various allergenic factors, including infections (bacteria, viruses, especially Coxsackie B virus, Chinese Taxillus Herb, etc.), foods (milk, eggs, fish, shrimp, etc.), medications (antibiotics, sulfonamides, antipyretics, sedatives, etc.), Mongolian snakegourd root, insect bites, and vaccinations, can trigger allergic reactions in individuals with sensitive constitutions. This leads to the production of autoantigens, followed by corresponding antibodies, forming antigen-antibody complexes that deposit on the walls of small blood vessels throughout the body. These complexes cause pathological changes primarily characterized by vasculitis. Therefore, this disease is classified as an autoimmune disorder.

bubble_chart Pathogenesis

The figure shows that immune responses causing tissue injury occur through two mechanisms: one is an immediate hypersensitivity reaction without complement involvement, where antibodies produced in the body react with re-entered antigens, leading to sterile inflammation in tissues and organs; the other involves complement, generating autoantigens that form immune complexes, resulting in tissue and organ injury.

bubble_chart Pathological Changes

Aseptic vasculitis is the main pathological change of this disease. In addition to capillaries, it can also involve small {|###|} arteries and small veins. Skin {|###|} injury is mainly seen in the dermal blood vessels, with acute inflammatory reactions, and infiltration of neutrophils and eosinophils around the blood vessels. Red blood cells exude through the vessel walls, leading to {|###|} edema, and swelling of collagen fibers adjacent to the {|###|} bleeding vessels. The vessel walls exhibit fibrinoid necrosis and interstitial {|###|} edema. In severe cases, necrotizing small {|###|} arteritis occurs. Intestinal changes are most common in the submucosa, presenting as significant {|###|} edema and hemorrhage, and in severe cases, submucosal {|###|} ulcers may develop. Renal changes primarily affect the glomeruli, showing focal or diffuse {|###|} injury. There is proliferation of capillary endothelial cells, local fibrosis and thrombosis, focal necrosis, and crescentic lesions may also be observed. Fluorescence microscopy reveals membranous and extensive proliferative changes in the glomerular capillary basement {|###|} membrane, along with deposits of IgG, C₃, and granular fibrin. In a few cases, the lesions may involve the heart, lungs, pleural {|###|} membrane, and cranial blood vessels, resulting in corresponding pathological changes.

bubble_chart Clinical Manifestations

The onset of the disease can be acute or gradual, with acute onset being more common. Most children have a history of upper respiratory tract infection 1–3 weeks before the onset. Non-specific manifestations such as irregular low-grade fever, lack of strength, headache, etc., may occur.

Skin symptoms: Rash is the main manifestation of this disease, most commonly seen densely distributed around the distal lower limbs and ankle joints. It may also appear on the buttocks and upper limbs, and occasionally on the face, but is rare on the trunk. The morphology and color of the rash can vary. Initially, it presents as small urticaria or pink papules, which blanch upon pressure. The color then deepens, forming erythema. Pinpoint hemorrhages may occur at the center of the erythema, gradually changing from pink to dark purple, forming purpura. Purpuric lesions may coalesce into larger patches. Finally, the lesions turn brown and fade without leaving scars. Additionally, erythema multiforme and erythema nodosum may occur. Angioneurotic edema can be seen on the head, eyelid, lips, hands, feet, kidneys, and perineum. Sometimes, the swollen areas may be tender.

Gastrointestinal symptoms: These are relatively common, occurring in about two-thirds of children, clinically referred to as the "abdominal type." The most common symptom is abdominal pain, often severe colicky pain, typically around the umbilicus but may also occur elsewhere. Three-quarters of affected children may exhibit tenderness. Vomiting may accompany the pain, followed by bloody stools, with severe cases presenting as bloody, watery stools. Hematemesis is rare. Misdiagnosis as acute diarrhea is common, especially before the appearance of the rash, leading to unnecessary exploratory laparotomy in many cases. A few patients may develop complications such as intussusception, and rarely, intestinal obstruction, perforation, or hemorrhagic necrosis of the small intestine.

Joint symptoms: About half of the affected children may experience polyarticular, migratory arthralgia or arthritis, predominantly in the lower limb joints. Swelling is more pronounced when the rash is present around the joints. Clinically, this is termed the "articular type." Joint effusions are mostly serous. Joint symptoms usually resolve within a few days without leaving deformities.

Renal symptoms: Approximately one-third of children develop nephritis, with younger children being more susceptible. This may present as gross hematuria or microscopic hematuria. It typically appears 2–4 weeks after the onset of purpura but may also occur after the rash subsides or during the quiescent phase of the disease. Clinically, this is referred to as the "renal type." The severity varies, with mild cases being more common. Severe cases may lead to renal dysfunction, azotemia, and hypertensive encephalopathy. In a few cases, hematuria, proteinuria, or hypertension may persist for more than two years.

Other symptoms: Mixed-type cases may involve central nervous system symptoms, such as unconsciousness, optic neuritis, subarachnoid hemorrhage, Guillain-Barré syndrome, or, rarely, limb spasm. Abnormal electroencephalogram (EEG) findings are present in 75% of children, with normalization occurring within 6–20 months. Severe cases may exhibit transient electrocardiographic abnormalities due to myocardial hypoxia or ischemia. Rare reports include complications such as acute pancreatitis, orchitis, and pulmonary hemorrhage.

bubble_chart Auxiliary Examination

There are no specific laboratory findings for this disease. Anemia may be present in cases of significant bleeding. White blood cell count is grade II elevated, eosinophils are normal or elevated, platelets are normal, and bleeding time, clotting time, and clot retraction are all normal. Erythrocyte sedimentation rate is increased, C-reactive protein is common, and antistreptolysin O may be negative. Throat culture may reveal group A β-hemolytic streptococci. Serum IgA is grade I elevated. Urinalysis, electroencephalography, and electrocardiography can be used to assess kidney, brain, and heart conditions. Fecal occult blood tests monitor gastrointestinal bleeding. Renal biopsy can determine the nature of nephritis lesions and provides guidance for treatment and prognosis.

bubble_chart Diagnosis

Diagnostic Criteria Since skin disease manifestations are often typical, acute abdominal pain, arthralgia, and urinary changes also aid in diagnosis. The classification and diagnostic criteria for allergic purpura established by the American Bi Disease Association in 1990 are as follows: ① Typical skin purpura; ② Age of onset <20 years; ③ Acute abdominal pain; ④ Tissue biopsy showing neutrophil infiltration around small veins and small stirred pulse.

Among the above four criteria, meeting two or more allows for a diagnosis of allergic purpura.

Diagnosis is not difficult when skin manifestations are typical. However, cases with non-purpuric skin presentations or systemic symptoms appearing before the rash are prone to misdiagnosis.

bubble_chart Treatment Measures

There is currently no specific treatment, and comprehensive therapy is the main approach.

General Therapy: During the acute phase, bed rest is recommended. The diet should be protein-free and consist of a low-residue semi-liquid. For those with gastrointestinal bleeding, such as mild abdominal pain and positive fecal occult blood, a liquid diet may be used. For severe abdominal pain and visible bloody stools, fasting is advised. If bacterial infection is present before the onset of illness, penicillin treatment should be administered for 10 days. Efforts should be made to identify and avoid allergens. School-aged children with gastrointestinal or nephritis symptoms should resume school three months after symptoms disappear.

Hormone Therapy: Generally, hormone treatment is unnecessary for typical cases, as hormones are ineffective for purpura. For patients with gastrointestinal bleeding, hydrocortisone 5–10 mg/kg/day may be administered intravenously. Once symptoms subside, oral prednisone can be used instead, with a total treatment course of 2–3 weeks. For renal lesions, hormones show no significant efficacy, and immunosuppressants such as cyclophosphamide or azathioprine may be tried. Some adopt methylprednisolone pulse therapy, with 30 mg/kg administered intravenously over one hour every other day, for a total of six sessions per course. The efficacy requires further observation.

Other Therapies: Some use urokinase to treat purpuric nephropathy, which can promote diuresis and reduce swelling. Its mechanism involves reducing fibrin deposition in the glomeruli. The dosage is 10,000–20,000 units per intravenous injection, once daily for 20 days, with no reported side effects. Intravenous infusion of tangut anisodus alkaloid and vitamin C has an efficacy rate of 92%. For cases with only skin and joint symptoms, aspirin can alleviate joint swelling and pain. Traditional Chinese medicine attributes this condition to "yang macula" caused by pathogenic heat damaging the blood. The treatment focuses on clearing heat, removing toxins, cooling blood, and resolving stasis, often using modified Rhinoceros Horn Decoction. The prescription includes 3g of antelope horn, 15g of Lonicera, 9g of Arnebia, 9g of Forsythia, 9g of moutan bark, 9g of Salvia, 15g of unprocessed rehmannia root, and 6g of myrrh. For severe purpura, Purple Snow Bolus (0.3–0.6g infused) may be added. For hematochezia, add 9g of charred sanguisorba root and 9g of charred smoked plum, along with 1.5g of Sanqi powder (infused). During convalescence, Chinese date and donkey-hide gelatin may be added. For severe cases, injections of Salvia, Carthamus, and Sichuan Lovage Rhizome, among others, may be administered intravenously with glucose solution.

bubble_chart Prognosis

Patients without nephritis have a good prognosis, but those with a disease course lasting from one month to several months are prone to relapse. The intervals between relapses vary from weeks to months. Severe intestinal bleeding is generally manageable with appropriate treatment. Intracranial bleeding is rare. The prognosis of this disease is mainly related to the nature of kidney lesions. Some cases may persist for several years, but most patients with grade I kidney damage can gradually recover. A few severe cases may be accompanied by hypertensive encephalopathy and chronic renal failure, the latter often occurring several years after the onset of nephritis. It has been reported that the appearance of kidney lesions within the first three months of the disease or recurrent episodes accompanied by nephropathy often indicate a poor prognosis.

bubble_chart Differentiation

1. Idiopathic thrombocytopenic purpura Generally, no differentiation is needed based on rash morphology, distribution, and platelet count. Angioneurotic edema is commonly seen in allergic purpura but not in thrombocytopenic purpura.

2. Abdominal surgical diseases If acute abdominal pain occurs before the appearance of a rash, differentiation from appendicitis is necessary. When bloody stools are present, differentiation from intussusception or Meckel's diverticulum is required. Allergic purpura with abdominal pain as the earliest and main symptom is mostly seen in older children. For children presenting with acute abdominal pain, the possibility of allergic purpura should be considered, and a comprehensive examination of the skin, kidneys, and joints is necessary.

3. Bacterial infections Meningococcal septicemia, subacute bacterial endocarditis, and other septicemias can also present with purpura, sometimes requiring differentiation. The purpura caused by these diseases is due to thrombosis with central necrosis. However, affected children often present with sudden and severe illness, generally progressing rapidly to critical condition. Blood cultures are often positive.

When renal symptoms are prominent, differentiation from acute glomerulonephritis is necessary. For any child presenting with chronic kidney damage, a history of allergic purpura should be inquired about.