<unk>  on the chest If the rash has appeared, identifying this disease (making a differential diagnosis) requires only a visual examination, since very few diseases produce a rash in a dermatomal pattern (see map). However, herpes simplex virus (HSV) can occasionally produce a rash in such a pattern (zosteriform herpes simplex). When the rash is absent (early or late in the disease, or in the case of ),<unk>  can be difficult to diagnose. Apart from the rash, most symptoms can occur also in other conditions. Laboratory tests are available to diagnose<unk> . The most popular test detects VZV-specific IgM antibody in blood; this appears only during chickenpox or<unk>  and not while the virus is dormant. In larger laboratories, lymph collected from a blister is tested by polymerase chain reaction (PCR) for VZV DNA, or examined with an electron microscope for virus particles. Molecular biology tests based on in vitro nucleic acid amplification (PCR tests) are currently considered the most reliable. Nested PCR test has high sensitivity, but is susceptible to contamination leading to false positive results. The latest real-time PCR tests are rapid, easy to perform, and as sensitive as nested PCR, and have a lower risk of contamination. They also have more sensitivity than viral cultures. Differential diagnosis<unk>  can be confused with herpes simplex, dermatitis herpetiformis and impetigo, and skin reactions caused by contact dermatitis, candidiasis, certain drugs and insect bites.
Shingles
Insect bites and stings
Sealpox
Angina
Farmyard pox
Herpes simplex
Streptococcal intertrigo
Sciatica