In this video, we'll be reviewing a case in which the accurate diagnosis of this teenager's itchy skin allowed her doctor to build enough trust to tackle her broader health concerns. Jessica was a 15-year-old girl who came to the school based teen clinic complaining of several days of itching all over her body. The itching was worse at night and had become so intense that she couldn't sleep or focus on her schoolwork. She also admitted tearfully, that she felt guilty because the itching and sleep deprivation were making her become impatient with her two-year-old brother, Rodrigo, who had Down Syndrome and who Jessica normally enjoyed babysitting every day after school. Jessica reported no other symptoms and had no past health problems. When the doctor asked about her life and activities, Jessica shared that she had recently become sexually active with her boyfriend. Although she had always felt safe with him, she admitted that a couple of months ago her boyfriend had been briefly incarcerated at juvenile hall for possessing a knife on school property. She also said, that they only occasionally used condoms when having sex. And she was scared that the itching in the groin and genital area meant she had caught something bad from him. After completing the history, the physician asked Jessica to change into a gown for a complete skin exam. He saw extensive scratches on her hands, wrists, elbows, breasts, underarms, waist, buttocks, and groin. Examining those areas more closely he saw small red bumps, many of them crusted with blood from the scratching. It was one particular area between the webs of Jessica's fingers that gave him the best clue to the diagnosis. There he observe a thin, reddish-brown line, about one centimeter long, punctuated at one end by a red bump. He recognized the classic skin appearance of a scabies burrow. Scabies is a skin infestation caused by the arthropod Sarcoptes scabiei, which is spread from person to person through direct skin contact. Outbreaks are especially likely in overcrowded or institutional settings. And in this case, it turns out the Jessica's boyfriend had contracted scabies while sharing close living quarters with other teens at juvenile hall. He then passed it on to Jessica through sexual contact. Scabies mites mate on the skin surface. Then the female secretes proteolytic enzymes to burrow under the stratum corneum layer of the epidermis. Where it gradually extends its burrow, lays eggs along the way, and dies in place after about two months. The larvae hatch and mature within the burrow, then make their way back up to the skin surface, to either repeat the cycle on the same host or spread to a new patient. At any given time a typical patient harbors about 10 to 15 mites. The host immune system responds to scabies by mounting a Type IV hypersensitivity reaction. A type of cell mediated immune response. Langerhans cells and macrophages in the skin engulf antigens from the mites or their saliva and feces. The antigen presenting cells present mite antigens to the T cells, resulting in an expanded mite antigen specific T cell population. Eventually, the mite antigen specific T cells arrive back at the site of infestation. They recognize the mite antigens and secrete cytokines upon stimulation which induce an inflammatory response. All of this results in intensely itchy skin lesions. Type IV hypersensitivity reactions are a delayed type of reaction because the cell-mediated immune response takes time. So patients typically don't develop itching until three to six weeks after the primary infestation. To confirm Jessica's diagnosis in clinic, the doctor used a blade to obtain skin scrapings from between her fingers, where he saw the classic appearing burrow. When he viewed the specimen under the microscope, he saw a scabies mite, ova, and feces. The physician returned to Jessica's room and explained that her itching was caused by scabies and fortunately, there is a safe, effective treatment available. He prescribed a topical cream called permethrin and instructed her to massage it into her skin before going to bed that night. All the way from her neck, down to the soles of her feet. After leaving it on for eight hours she could wash it off in the shower. She should then repeat the treatment one to two weeks later to completely eliminate all the mites. The doctor strongly recommended that Jessica's boyfriend and all her close household contacts receive treatment as well especially her baby brother with Down Syndrome. Although scabies is normally a benign condition certain populations including the elderly, immunocompromised patients, and people with Down Syndrome are susceptible to an overwhelming and potentially dangerous scabies infestation, known as crusted scabies. Crusted scabies occurs when the patient doesn't mount an effective cell-mediated immune response to protect against the scabies mite. So they replicate unhindered until there are hundreds of thousands of mites on the patient's body. Unlike typical scabies, the patient develops red scaled patches which don't itch because the cell mediated immune response is not very robust. These patients are extremely vulnerable to super infection with bacteria which can then enter the blood stream though fissures in the skin and lead to bacteremia, and potentially sepsis. Before he sent her home, the doctor told Jessica that he was glad she came in because it gave them a chance to talk about some important health considerations for her now that she was sexually active. Jessica and her doctor discussed birth control and STD prevention. And Jessica agreed to undergo testing for sexually transmitted infections as well as a pregnancy test. All of these tests came back negative. At her follow-up visit, one week later, Jessica was relieved that her itching had subsided. She had also told her parents about the scabies diagnosis so they could seek treatment for her little brother who, fortunately, never developed any skin symptoms.