Anthrax differential diagnosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
The differential diagnosis of anthrax includes a wide range of infectious and non-infectious conditions. Depending on the mode of anthrax exposure in the patient (cutaneous, ingestion, inhalation or injection), there will be different forms of the disease.[1] A history of exposure to contaminated animal materials, occupational exposure, and living in an endemic area, is crucial when considering the diagnosis of anthrax. Additional tests to isolate Bacillus anthracis are required to differentiate anthrax from other diagnoses, thereby confirming the correct etiologic agent.
Differential Diagnosis
Cutaneous Anthrax
- A history of exposure to contaminated animal materials, occupational exposure, and living in an endemic area is crucial when considering a diagnosis of anthrax. A painless, pruritic papule, surrounding vesicles and edema, usually on an exposed region of the body should raise concern of cutaneous anthrax, which is confirmed by the demonstration of Gram-positive encapsulated bacilli on the lesion, and/or positive culture for Bacillus anthracis and/or positive specialized tests.
- The differential diagnosis of the anthrax eschar includes a wide range of infectious and non-infectious conditions, including:[1]
| Disease | Findings |
|---|---|
| Boil (early lesion) | Skin disease caused by the inflammation of hair follicles, thus resulting in the localized accumulation of pus and necrotic tissue. Individual boils may cluster together and form an interconnected network of boils called carbuncles. In severe cases, boils may develop to form abscesses |
| Arachnid bites | Spider bites can cause allergic reactions. Symptoms of a spider bite may include erythema, pain and edema of the site |
| Erysipelas | Acute streptococcus bacterial infection of the dermis, resulting in inflammation and characteristically extending into underlying fat tissue. Erythematous skin lesion that enlarges rapidly and has a sharply demarcated raised edge. It appears as a red, swollen, warm, hardened and painful rash, similar in consistency to an orange peel. More severe infections can result in vesicles, bullae, and petechiae, with possible skin necrosis. Lymph nodes may be swollen, and lymphedema may occur. Occasionally, a red streak extending to the lymph node can be seen. The infection may occur on any part of the skin including the face, arms, fingers, legs and toes, but it tends to favor the extremities. Fat tissue is most susceptible to infection, along with facial areas typically around the eyes, ears, and cheeks. Repeated infection of the extremities can lead to chronic lymphadenitis |
| Glanders | Infectious disease that occurs primarily in horses, mules, and donkeys. It is caused by infection by the bacterium Burkholderia mallei, usually by ingestion of contaminated food or water. Symptoms of glanders include the formation of nodular lesions in the lungs and ulceration of the mucous membranes in the upper respiratory tract. The acute form results in coughing, fever and the release of infectious nasal discharge, followed by septicemia and death within days. In the chronic form, nasal and subcutaneous nodules develop, eventually ulcerating. Death can occur within months, while survivors act as carriers. |
| Plague | |
| Syphilitic chancre | |
| Ulceroglandular tularemia | |
| Clostridial infection | |
| Rickettsial diseases | |
| Rhizomucor infections | |
| Orf | |
| Vaccinia | |
| Cowpox | |
| Rat-bite fever | |
| Leishmaniasis | |
| Ecthyma gangrenosum | |
| Herpes |
- Generally these other diseases and conditions lack the characteristic edema of anthrax. The absence of pus, the lack of pain, and the patient’s occupation may provide further diagnostic clues. The outbreak of Rift Valley fever, initially thought to be anthrax in livestock, also affected numerous humans.
- In the differential diagnosis of the severe forms, orbital cellulitis, dacryocystitis and deep tissue infection of the neck, should be considered in the case of severe anthrax lesions involving the face, neck and anterior chest wall. Necrotizing soft tissue infections, particularly group A streptococcal infections and gas gangrene, and severe cellulitis due to staphylococci, should also be considered in the differential diagnosis of severe forms of cutaneous anthrax. Gas and abscess formation are not observed in patients with cutaneous anthrax. Abscess formation is only seen when the lesion is infected with other bacteria, such as streptococci or staphylococci.
Ingestional Anthrax (Oropharyngeal and Gastrointestinal Anthrax)
Oropharyngeal Anthrax
- The list of differential diagnosis of oropharyngeal anthrax includes:
| Disease | Findings |
|---|---|
| Diphtheria | |
| Complicated tonsillitis | |
| Streptococcal pharyngitis | |
| Vincent's angina | |
| Ludwig's angina | |
| Parapharyngeal abscess | |
| Deep-tissue infection of the neck |
Gastrointestinal Anthrax
- The list of differential diagnosis of gastrointestinal anthrax includes:
| Disease | Findings |
|---|---|
| Food poisoning (in the early stages of intestinal anthrax) | |
| Acute abdomen | |
| Hemorrhagic gastroenteritis | |
| Necrotizing enteritis caused by Clostridium perfringens | |
| Dysentery (amebic or bacterial)[1] |
Inhalational Anthrax (Pulmonary, Mediastinal, and Respiratory Anthrax)
- The list of differential diagnosis of inhalation anthrax includes:
| Disease | Findings |
|---|---|
| Mycoplasma pneumoniae | |
| Legionnaires' disease | |
| Psittacosis | |
| Tularemia | |
| Q fever | |
| Viral pneumonia | |
| Histoplasmosis | |
| Coccidiomycosis | |
| Malignancy[1] |
Anthrax Meningitis
- Meningitis is a potential complication of anthrax infection. The list of differential diagnosis of anthrax meningitis includes:
| Disease | Findings |
|---|---|
| Acute meningitis | |
| Cerebral malaria | |
| Subarachnoid hemorrhage |
- The definitive diagnosis is obtained by visualization of the capsulated bacilli in the cerebrospinal fluid and/or by culture.[1]
Anthrax Sepsis
- Sepsis is a potential complication of anthrax infection.
| Disease | Findings |
|---|---|
| Sepsis |
- The definitive diagnosis of anthrax is made by the isolation of Bacillus anthracis from the primary lesion, from blood cultures or by detection of the toxin or DNA of B. anthracis in these specimens.[1]