Petechiae

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Petechiae

Definition and Morphology

Petechiae are capillary hemorrhages presenting as nonblanching, pinpoint (≤3-4 mm), red, blue, or purple spots resulting from extravasation of blood from small dermal capillaries. They are distinguished from purpura (5-9 mm) and ecchymoses (≥1 cm) by size. The key clinical test is diascopy (glass pressure): petechiae do not blanch, confirming true hemorrhage rather than vascular dilation.

Shape: round to oval, occasionally targetoid
Distribution: most often dependent body parts (lower extremities), but may be widespread
Texture: flat (nonpalpable), unless associated with inflammation

Round to oval petechiae, <3 mm in diameter, on the arm

Petechiae: round to oval, <3 mm in diameter - Goldman-Cecil Medicine

Pathophysiology

Petechiae form by three mechanisms:

Thrombocytopenia / platelet dysfunction - inadequate platelet plug formation allows capillary bleeding (most common cause)
Increased intravascular pressure - venous obstruction, Valsalva, violent coughing, or vomiting forces RBCs through capillary walls
Vascular wall damage - infection, vasculitis, or nutritional deficiency weakens the capillary endothelium

Differential Diagnosis

Causes of Macular Petechiae (≤4 mm)

Category	Cause
Platelet disorder	Thrombocytopenia (platelets <50,000/µL) - ITP, drug-induced, hematologic malignancy
Platelet dysfunction	Renal or hepatic insufficiency, von Willebrand disease
Increased venous pressure	Tourniquet, retching, violent coughing (confined above nipple line)
Nutritional	Vitamin C deficiency (scurvy)
Vascular/pigmented	Schamberg disease (pigmented purpuric dermatitis) - idiopathic capillaritis; cayenne-pepper petechiae on lower legs
Dysproteinemia	Waldenström macroglobulinemia
Infectious	Meningococcemia, Rocky Mountain spotted fever, pneumococcal bacteremia, parvovirus

The Critical "Fever + Petechiae" Scenario

This combination demands urgent evaluation. The differential includes:

Neisseria meningitidis (meningococcemia) - most feared; incidence ~7-11% in hospitalized patients with fever + petechiae
Disseminated intravascular coagulation (DIC)
Rocky Mountain spotted fever (RMSF)
Streptococcus pyogenes bacteremia
Pneumococcal bacteremia
Henoch-Schönlein purpura (IgA vasculitis) - notably WITHOUT thrombocytopenia
Leukemia
Various viral infections

Mechanical petechiae from vomiting/coughing are limited to the skin above the nipple line. Petechiae from serious bacterial infection (SBI) have any distribution.

Palpable vs. Nonpalpable: A Key Distinction

Feature	Nonpalpable	Palpable
Mechanism	Simple capillary extravasation (thrombocytopenia, platelet dysfunction, pressure)	Inflammatory vessel wall damage (vasculitis)
Key causes	ITP, Schamberg, scurvy, mechanical	Leukocytoclastic vasculitis, IgA vasculitis, meningococcemia, RMSF, DIC
Urgency	Variable	Potentially life-threatening

Palpable purpura/petechiae always require evaluation for vasculitis and, in the right context, infectious causes - Goldman-Cecil Medicine

Specific Conditions

Schamberg Disease

The most common cause of isolated petechiae in adults. Idiopathic capillaritis causing cayenne-pepper-colored petechiae on lower legs with yellow-brown hyperpigmented patches. Benign, but new crops appear over time. Treated with topical steroids, ascorbic acid 500 mg twice daily ± rutoside 50 mg twice daily.

ITP (Immune Thrombocytopenic Purpura)

Typically presents as mild mucocutaneous bleeding and petechiae or incidental thrombocytopenia. Bleeding risk highest when platelets <30 × 10⁹/L.

Meningococcemia

Classic petechial/purpuric rash in a febrile, ill-appearing patient. The lesions may rapidly evolve into confluent purpura fulminans. This is a medical emergency.

RMSF

Petechiae typically appear after 3-5 days of fever; may start on wrists/ankles and spread centrally, including palms and soles.

Forensic context

Petechial hemorrhages in conjunctivae/sclerae are classical in asphyxial deaths from strangulation (also called Tardieu spots on visceral surfaces), though they are nonspecific and may be seen in many non-fatal conditions.

Diagnostic Workup

CBC with differential - platelet count (thrombocytopenia is the most common cause)
Peripheral blood smear - platelet morphology, blast cells, schistocytes (TTP/HUS)
Coagulation studies - PT, PTT, fibrinogen, D-dimer (DIC)
Blood culture if febrile (bacteremia, meningococcemia)
CRP - elevated in SBI
Skin biopsy - determines vessel size involved, degree of inflammation, type of damage (leukocytoclastic vs. granulomatous), presence of organisms or occlusions
Direct immunofluorescence - identifies IgA deposits (IgA vasculitis), immune complexes on vessel walls

In children with fever + petechiae: abnormal WBC (<5,000 or >15,000/mm³) or abnormal coagulation are predictive of invasive bacteremia - admit and treat empirically until cultures result. Well-appearing children with normal WBC, CRP, and coagulation can be discharged with close follow-up. - Rosen's Emergency Medicine

Treatment

Treatment is directed at the underlying cause. Supportive care includes local wound care and prevention of secondary infection for superficial lesions.

Sources: Symptom to Diagnosis, 4th ed. | Goldman-Cecil Medicine | Rosen's Emergency Medicine | Fitzpatrick's Dermatology 5th ed.

Ecchymoses

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Ecchymoses

Definition and Morphology

Ecchymoses (singular: ecchymosis) are subcutaneous hemorrhages ≥1 cm in diameter, commonly called bruises. They result from extravasation of blood from small vessels into the dermis and subcutaneous tissue, producing nonblanching discoloration. They differ from petechiae (<4 mm) and purpura (4-10 mm) by size alone, though the underlying mechanisms overlap.

Shape: typically geometric, rectangular, or linear when trauma-induced; irregular when from systemic disease
Color evolution: red/purple → blue-green → yellow-brown, reflecting sequential degradation of hemoglobin to biliverdin to bilirubin/hemosiderin
Texture: flat (nonpalpable); palpable when blood volume is large enough to form a hematoma
Blood is typically resorbed within ~2 weeks; postinflammatory hyperpigmentation may persist

Pathophysiology: Two Broad Mechanisms

Ecchymoses require blood to escape vessel walls. This occurs via two main routes:

1. Procoagulant defects

Inadequate clotting factors or platelets fail to seal micro-tears. Even minor trauma leads to disproportionate bleeding.

2. Poor dermal connective tissue support

The dermis normally anchors and buttresses capillaries. When this scaffolding is lost, minor mechanical stress ruptures vessels that would otherwise hold. Coagulation may be entirely normal.

Differential Diagnosis of Macular Ecchymoses (≥1 cm)

Procoagulant Defects

Cause	Mechanism
Anticoagulant therapy (warfarin, heparin, DOACs)	Impairs clotting cascade
Hepatic insufficiency	Reduced synthesis of factors II, V, VII, IX, X, fibrinogen
Vitamin K deficiency	Impairs carboxylation of factors II, VII, IX, X
Disseminated intravascular coagulation (DIC)	Consumption of clotting factors + platelets
Thrombocytopenia	Insufficient platelet plug formation
Platelet function defects	Von Willebrand disease, medication-induced (ASA, NSAIDs), uremia

Poor Dermal Support

Cause	Features
Solar (actinic/senile) purpura	Aging + UV damage degrades dermal connective tissue; ecchymoses on extensor forearms; benign, cosmetically bothersome
Corticosteroid purpura	Topical or systemic steroids cause dermal atrophy; can be widespread with Cushing's syndrome
Vitamin C deficiency (scurvy)	Impaired collagen synthesis weakens perivascular connective tissue
Systemic amyloidosis	AL or ATTR amyloid deposits weaken vessel walls; "pinch purpura" around eyes classic
Ehlers-Danlos syndrome	Defective fibrillar collagen; skin velvety and thin, bruises easily from childhood; joint hypermobility, pseudotumors

Miscellaneous

Trauma - most common cause overall; geometric/linear shape, trauma-prone sites (dorsal hand, shin, lateral thigh)
Gardner-Diamond syndrome (autoerythrocyte sensitization) - recurrent painful ecchymoses on palmar surface of fingers; predominantly women; Doppler evaluation negative
Papular purpuric gloves and socks syndrome

Senile (Actinic/Solar) Purpura - A Common Entity

Senile purpura is worth detailing as it is the most frequent cause of ecchymoses in older adults:

Mechanism: Age-related skin thinning + chronic UV damage degrades dermal connective tissue, leaving microvasculature unsupported and fragile. Minor bumps rupture venules.
Distribution: Extensor surfaces of forearms and hands (sun-exposed areas)
Appearance: Bright purple-red ecchymoses that resolve over 1-2 weeks, leaving brown hyperpigmentation from hemosiderin
Aggravating factors: Aspirin, anticoagulants (very common in the elderly), NSAIDs
Coagulation studies: Normal
Treatment: No specific treatment; vitamin C and topical retinoids may help maintain dermal collagen. The condition is benign.

"Age-related skin thinning and sun-induced damage of the connective tissue of the dermis results in inadequate support and increased fragility of the microvasculature. As a result, minor trauma of aged photodamaged skin can lead to vessel rupture." - Fitzpatrick's Dermatology

Distinguishing Ecchymoses from Petechiae/Purpura

Feature	Petechiae	Purpura	Ecchymoses
Size	≤4 mm	4-10 mm	>10 mm (≥1 cm)
Most common cause	Thrombocytopenia	Vasculitis / thrombocytopenia	Trauma / anticoagulation / dermal fragility
Shape	Round, pinpoint	Variable	Geometric if traumatic; irregular if systemic
Blanching	No	No	No
Palpable?	No	Sometimes (vasculitis)	Sometimes (hematoma)

Coagulation Factor Defects vs. Platelet Defects: A Pattern Distinction

Platelet disorders (including ecchymoses) - mucocutaneous bleeding, petechiae, purpura; bleeding after superficial cuts; prolonged bleeding time
Coagulation factor defects (hemophilia, etc.) - deep tissue bleeding, hemarthrosis, muscle hematomas; bleeding after surgery/trauma; prolonged PT or aPTT
Ecchymoses can occur in both, but large deep ecchymoses without clear trauma in a young patient should raise suspicion for hemophilia or other factor deficiencies

Diagnostic Workup

History: trauma exposure, medications (anticoagulants, steroids, ASA), age, sun exposure, alcohol/liver disease, family history of bleeding
CBC with platelets - thrombocytopenia
PT/INR - extrinsic pathway (warfarin effect, liver disease, vitamin K deficiency)
aPTT - intrinsic pathway (hemophilia, heparin)
Fibrinogen + D-dimer - DIC
Liver function tests - hepatic insufficiency
Vitamin C level if scurvy suspected (perioral bleeding, perifollicular hemorrhage, gingival changes)
Peripheral smear - schistocytes (TTP/HUS), blast cells
Skin biopsy - when vascular disease or amyloidosis suspected; Congo red staining for amyloid

Treatment

Treatment is directed at the underlying cause:

Reverse anticoagulation if excessive (vitamin K, PCC, FFP as appropriate)
Treat DIC (manage precipitant, supportive)
Corticosteroid purpura: minimize steroid dose; photoprotection for solar purpura
Vitamin C replacement for scurvy (rapid resolution)
Platelet transfusion or ITP treatment for platelet-mediated cases

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