Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are two forms of a life-threatening skin condition, in which cell death causes the epidermis to separate from the dermis. The syndrome is thought to be a hypersensitivity complex that affects the skin and the mucous membranes. The most well-known causes are certain medications, but it can also be due to infections, or more rarely, cancers.
Synonyms: PN, nodular prurigo, Hyde's disease, picker nodules, lichen corneus obtusus, nodular lichen simplex chronicus, nodular neurodermatitis circumscripta
This is a chronic inflammatory dermatosis of unknown aetiology. It causes a papulonodular eruption which is intensely itchy. Patients may be driven to distraction by the itch/scratch cycle that the disease induces, as may their doctors by their inability to treat the condition effectively.
The constant scratching leads to the development of discrete, excoriated, nodular, hyperpigmented/purpuric lesions with crusted or scaly surfaces. The scaling, thickening and hyperkeratosis of the skin, induced by scratching, is known as lichen simplex chronicus which may also present in a plaque-like form.
It predominantly affects the extensor aspects of the lower limbs but also commonly affects the arms and sometimes other areas of the body. Calcitonin gene-related peptide and substance P immunoreactive nerves are markedly increased in number and activity in the skin of prurigo nodularis sufferers, compared with normal skin.[1] Whether this represents a causative aetiology or arises as a result of chronic scratching and skin irritation is not known. One study found hypoplasia of epidermal sensory nerves in the skin of prurigo nodularis sufferers even in areas where pruritus was not a problem.[2]
Epidemiology
• The condition appears to be relatively common, particularly among patients who have some of the associated/precipitating conditions but there are no surveys of its prevalence in the general population.
• It was originally described as a disease of middle-aged women, although currently there is not thought to be any convincing evidence of a female preponderance but it does appear to be more common in middle-aged people.[3]
• In a modern, urban setting it appears to be the second most common dermatosis affecting those with HIV and relatively low CD4 counts.[4]
One study found that the development of prurigo nodularis in HIV patients was a sign of severe immunosuppression.[5]
• It is thought that the prevalence of so-called neurotic excoriations, of which an unknown proportion of cases of prurigo nodularis might be a manifestation, is about 2% in dermatology clinics and 9% in those with an underlying cause for pruritus.[6]
Histoplasmosis
Histoplasmosis (also known as "Cave disease,"[1] "Darling's disease,"[1] "Ohio valley disease,"[1] "Reticuloendotheliosis,"[1] "Spelunker’s Lung" and "Caver's disease") is a disease caused by the fungus Histoplasma capsulatum. Symptoms of this infection vary greatly, but the disease affects primarily the lungs.[2] Occasionally, other organs are affected; this is called disseminated histoplasmosis, and it can be fatal if left untreated.
Histoplasmosis is common among AIDS patients because of their suppressed immunity.[3] In immunocompetent individuals, past infection results in partial protection against ill effects if reinfected.
Histoplasma capsulatum is found in soil, often associated with decaying bat guano or bird droppings. Disruption of soil from excavation or construction can release infectious elements that are inhaled and settle into the lung.
