Another cause for variation, the immune status of the patient can alter the expression of the disease.
Consider zoster (shingles) infection. In immunocompromised patients, such as a patient with AIDS, the infection can present with erosions, ulcers, eschars, or even papules rather than the typical vesicles seen in the immunocompetent patient.
Zoster (shingles): Grouped umbilicated vesicles on an erythematous base in a dermatomal distribution is the classic presentation
This immunocompetent elder patient has a more severe case of zoster, with skin ulcers following the vesicles
In the immunocompromised patient, zoster can be extremely inflammatory with resulting necrosis and thick eschars
In an AIDS patient, zoster can present with thick crusts. The dermatomal distribution was the diagnostic clue