Smallpox differential diagnosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
Prior to its eradication, smallpox would need to be differentiated from other diseases that cause a vesicular rash and a fever including chickenpox (which was often mistaken for smallpox), herpes zoster and erythema multiforme.
Differentiating Smallpox from other Diseases
- Insect bites - In an insect bite, the insect injects formic acid, which can cause an immediate skin reaction often resulting in a rash and swelling in the injured area, often with formation of vesicles.
- Kawasaki disease - commonly presents with high and persistent fever, red mucous membranes in mouth, "strawberry tongue", swollen lymph nodes and skin rash in early disease, with peeling off of the skin of the hands, feet and genital area.
- Measles - commonly presents with high fever, coryza and conjunctivitis, with observation of oral mucosal lesions (Koplik's spots), followed by widespread skin rash.
- Monkeypox - presentation is similar to smallpox, although it is often a milder form, with fever, headache, myalgia, back pain, swollen lymph nodes, a general feeling of discomfort, and exhaustion. Within 1 to 3 days (sometimes longer) after the appearance of fever, the patient develops a papular rash, often first on the face. The lesions usually develop through several stages before crusting and falling off.
- Rubella - commonly presents with a facial rash which then spreads to the trunk and limbs, fading after 3 days, low grade fever, swollen glands, joint pains, headache and conjunctivitis. The rash disappears after a few days with no staining or peeling of the skin. Forchheimer's sign occurs in 20% of cases, and is characterized by small, red papules on the area of the soft palate.
- Atypical measles - symptoms commonly begin about 7-14 days after infection and present as fever, cough, coryza and conjunctivitis. Observation of Koplik's spots is also a characteristic finding in measles.
- Coxsackievirus - most commonly caused disease is the Coxsackie A disease, presenting with hand, foot and mouth disease. It may be asymptomatic or cause mild symptoms, or it may produce fever and painful blisters in the mouth (herpangina), on the palms and fingers of the hand, or on the soles of the feet. There can also be blisters in the throat, or above the tonsils. Adults can also be affected. The rash, which can appear several days after high temperature and painful sore throat, can be itchy and painful, especially on the hands/fingers and bottom of feet.
- Acne - typical of teenagers, usually appears on the face and upper neck, but the chest, back and shoulders may have acne as well. The upper arms can also have acne, but lesions found there are often keratosis pilaris, not acne. The typical acne lesions are comedones and inflammatory papules, pustules, and nodules. Some of the large nodules were previously called "cysts"
- Secondary syphilis - commonly presents with gneralized systemic symptoms such as malaise, fatigue, headache and fever. Skin eruptions may be subtle and asymptomatic Classically described as 1) non-pruritic bilateral symmetrical mucocutaneous rash; 2) non-tender regional lymphadenopathy; 3) condylomata lata; and 4) patchy alopecia.
- Molluscum contagiosum - lesions are commonly flesh-colored, dome-shaped, and pearly in appearance. They are often 1-5 millimeters in diameter, with a dimpled center. Generally not painful, but they may itch or become irritated. Picking or scratching the lesions may lead to further infection or scarring. In about 10% of the cases, eczema develops around the lesions. They may occasionally be complicated by secondary bacterial infections.
- Mononucleosis - Common symptoms include low-grade fever without chills, sore throat, white patches on tonsils and back of the throat, muscle weakness and sometime extreme fatigue, tender lymphadenopathy, petechial hemorrhage and skin rash.
- Rat-bite fever - commonly presents with fever, chills, open sore at the site of the bite and rash, which may show red or purple plaques.
- Parvovirus B19 - the rash of fifth disease is typically described as "slapped cheeks," with erythema across the cheeks and sparing the nasolabial folds, forehead, and mouth.
- Cytomegalovirus - common symptoms include sore throat, swollen lymph nodes, fever, headache, fatigue, weakness, muscle aches and loss of appetite.
- Scarlet fever - common includes fever, punctate red macules on the hard and soft palate and uvula (Forchheimer's spots), bright red tongue with a "strawberry" appearance, sore throat and headache and lymphadenopathy.
- Rocky Mountain spotted fever - symptoms may include maculopapular rash, petechial rash, abdominal pain and joint pain.
- Stevens-Johnson syndrome - symptoms may include fever, sore throat and fatigue. Commonly presents ulcers and other lesions in the mucous membranes, almost always in the mouth and lips but also in the genital and anal regions. Those in the mouth are usually extremely painful and reduce the patient's ability to eat or drink. Conjunctivitis of the eyes occurs in about 30% of children. A rash of round lesions about an inch across arises on the face, trunk, arms and legs, and soles of the feet, but usually not the scalp.
- Drug eruptions