bubble_chart Overview

Allergic purpura falls within 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 pediatric 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 reported case being three months old. The disease occurs more frequently in winter and spring and less often in summer.

bubble_chart Etiology

disease cause

Various sensitizing factors, including infections (bacteria, viruses, especially Coxsackie B virus, Chinese Taxillus Herb, insects, etc.), foods (milk, egg, fish, shrimp, etc.), drugs (antibiotics, sulfonamides, antipyretics and analgesics, sedatives and anticonvulsants, etc.), mongolian snakegourd root, insect bites, vaccinations, etc., can trigger allergic reactions in individuals with a sensitive constitution, leading to the production of autoantigens. These autoantigens then generate corresponding antibodies, forming antigen-antibody complexes that deposit on the walls of small blood vessels throughout the body, causing pathological changes primarily characterized by vasculitis. Therefore, this disease is classified as an autoimmune disorder.

mechanism of disease

As shown in the diagram, the immune response causing tissue injury occurs through two pathways: one is an immediate-type hypersensitivity reaction without complement involvement, where antibodies produced in the body react with antigens that re-enter the body, resulting in aseptic inflammation of tissues and organs; the other pathway involves complement, generating autoantigens and forming autoantigen-antibody complexes, leading to tissue and organ injury.

pathological changes

Aseptic vasculitis is the primary pathological feature of this disease, affecting not only capillaries but also small stirred pulse and venules. Skin injury is mainly observed in the dermal blood vessels, with acute inflammatory reactions and perivascular infiltration of neutrophils and eosinophils. Red blood cells extravasate through the vessel walls, causing edema, and the collagen fibers near the proximal bleeding vessels swell. The vessel walls exhibit fibrinoid necrosis and interstitial edema. In severe cases, necrotizing small stirred pulse arteritis occurs. Intestinal changes are most common in the submucosa, presenting as significant edema and hemorrhage, with severe cases leading to mucosal ulcers. Renal changes primarily involve the glomeruli, showing focal or diffuse injury. Capillary endothelial hyperplasia, local fibrosis, 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, pathological changes may involve the heart, lungs, pleura, and cranial blood vessels, resulting in corresponding pathological alterations.

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 to 3 weeks before 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 rarely on the face or trunk. The morphology and color of the rash can vary. Initially, it presents as small urticaria or pink papules that blanch with pressure. The color then deepens, forming erythema. Pinpoint hemorrhages may occur in the center of the erythema, gradually changing from pink to dark purple, which is known as purpura. Purpura may coalesce into patches. Finally, the color turns brown and fades without leaving marks. Additionally, there may be erythema multiforme and nodular erythema. Angioneurotic edema can occur on the head, eyelid, lips, hands, feet, kidneys, and perineum. Sometimes, the swollen areas may be tender.

Gastrointestinal symptoms: These are relatively common, seen in about two-thirds of children, clinically referred to as the abdominal type. The most common symptom is abdominal pain, often severe colicky pain, occurring around the umbilicus or other areas, with tenderness in three-quarters of the children. Vomiting may also occur. Subsequently, bloody stools may appear, 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 exploratory laparotomy in many cases. A few patients may develop intussusception, and rarely, intestinal obstruction, perforation, or hemorrhagic necrotic small intestine inflammation.

Joint symptoms: About half of the children may experience polyarticular, migratory arthralgia or arthritis, most commonly in the lower limb joints. Swelling is more pronounced in joints surrounded by rashes. Clinically, this is referred to as the "articular type." Joint effusions are mostly serous. Joint symptoms usually resolve within a few days without leaving deformities.

Renal symptoms: About 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 to 4 weeks after the onset of purpura but may also occur after the rash subsides or during the disease's quiescent phase. 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 over 2 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. 75% of children show abnormal EEG findings, which normalize within 6 to 20 months. Severe cases may exhibit temporary ECG abnormalities due to myocardial hypoxia or ischemia. Rare reports include complications such as acute pancreatitis, orchitis, and pulmonary hemorrhage.

﹝Auxiliary examinations﹞

There are no specific laboratory findings for this disease. Anemia may be present in cases of significant bleeding. White blood cell count may show grade II elevation, with eosinophils being normal or elevated. Platelet count, bleeding time, clotting time, and clot retraction are all normal. ESR is increased, and C-reactive protein, common bletilla tuber, and antistreptolysin O may be negative. Throat cultures may reveal group A β-hemolytic streptococci. Serum IgA may show grade I elevation. Urinalysis, EEG, and ECG can help assess renal, cerebral, and cardiac conditions. Fecal occult blood tests monitor gastrointestinal bleeding. Renal biopsy can determine the nature of nephritis lesions, providing guidance for treatment and prognosis.

bubble_chart Diagnosis

Diagnostic Criteria Since skin disease is usually typical, acute abdominal pain, arthralgia, and urinary changes are also helpful for 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 pulses.

Among the above four criteria, meeting two or more can lead to a diagnosis of allergic purpura.

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

bubble_chart Treatment Measures

Treatment Measures:

There is currently no specific therapy, and comprehensive treatment 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 occult blood in stool, 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 symptoms, penicillin should be administered for 10 days. Efforts should be made to identify and avoid allergens. School-aged children with gastrointestinal or nephritis symptoms should return to school 3 months after symptoms disappear.

Hormone Therapy: Generally, hormone therapy is not necessary for typical cases, as hormones are ineffective for purpura. For patients with gastrointestinal bleeding, hydrocortisone 5–10 mg/kg·d may be administered intravenously. After symptoms subside, prednisone can be taken orally, 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 1 hour every other day, for a total of 6 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 be used to reduce joint swelling and pain. Chinese medicine attributes this condition to "yang macula" caused by pathogenic heat damaging the blood. The treatment focuses on clearing heat and 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, 9g of charred sanguisorba and 9g of charred smoked plum are added, along with 1.5g of Sanqi powder infused. During convalescence, Chinese date and donkey-hide gelatin may be included. 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 interval between relapses varies from weeks to months. Severe intestinal bleeding is generally manageable with appropriate treatment. Intracranial bleeding is rare. The prognosis of the 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 gradually recover. A few severe cases may be accompanied by hypertensive encephalopathy and chronic renal failure, with the latter often occurring several years after the onset of nephritis. It has been reported that the prognosis is often poor when kidney lesions appear within the first three months of the disease or when the condition recurs and is accompanied by nephropathy.

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 Before the appearance of the rash, if acute abdominal pain occurs, differentiation from appendicitis is necessary. When bloody stools appear, 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 bacteremia, 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 necrosis at the center. However, the condition of affected children is often acute and rapidly critical. Vascular culture is usually positive.

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