The term leukemoid reaction describes an increased
white blood cell count (> 50,000 cells/μL), which is a physiological response to stress or infection (as opposed to a primary blood malignancy, such as leukemia). It often describes the presence of immature cells such as myeloblasts or red blood cells with nuclei in the peripheral blood. It may be lymphoid or myeloid. Causes
As noted above, a leukemoid reaction is typically a response to an underlying medical issue. Causes of leukemoid reactions include:
Severe hemorrhage (retroperitoneal hemorrhage)
Drugs
Use of sulfa drugs
Use of dapsone
Use of glucocorticoids
Use of G-CSF or related growth factors
All-trans retinoic acid (ATRA)
Ethylene glycol intoxication
Infections
Clostridium difficile
Tuberculosis
Pertussis
Infectious mononucleosis (lymphocyte predominant)
Visceral larva migrans (eosinophil predominant)
Asplenia
Diabetic ketoacidosis
Organ necrosis
Hepatic necrosis
Ischemic colitis
As a feature of trisomy 21 in infancy (incidence of ~10%)
As a paraneoplastic phenomenon (rare)

Diagnosis
Conventionally, a leukocytosis exceeding 50,000 WBC/mm3 with a significant increase in early neutrophil precursors is referred to as a leukemoid reaction. The peripheral blood smear may show myelocytes, metamyelocytes, promyelocytes, and rarely myeloblasts; however, there is a mixture of early mature neutrophil precursors, in contrast to the immature forms typically seen in acute leukemia. Serum leukocyte alkaline phosphatase is normal or elevated in leukemoid reaction, but is depressed in chronic myelogenous leukemia. The bone marrow in a leukemoid reaction, if examined, may be hypercellular but is otherwise typically unremarkable.Leukemoid reactions are generally benign and are not dangerous in and of themselves, although they are often a response to a significant disease state (see Causes above).
Juvenile xanthogranuloma  is a form of histiocytosis, classified as "non-Langerhans cell histiocytosis", or more specifically, "type 2".It is a rare skin disorder that primarily affects children under one year of age but can also be found in older children and adults. It was first described in 1905 by Adamson. In 5% to 17% of people, the disorder is present at birth, but the median age of onset is two years. JXG is a benign idiopathic cutaneous granulomatous tumor and the most common form of non-Langerhans cell histiocytosis (non-LHC). The lesions appear as orange-red macules or papules and are usually located on the face, neck, and upper trunk. They may also appear at the groin, scrotum, penis, clitoris, toenail, palms, soles, lips, lungs, bone, heart, and gastrointestinal tract more rarely. JXG usually manifests with multiple lesions on the head and neck in cases with children under six months of age. The condition usually resolves spontaneously over one to five years. A biopsy of the lesion is critical to confirm the diagnosis. Ocular JXG manifests in up to 10% of people with JXG and may affect their vision. The presence of JXG in the eye can cause spontaneous hyphema, secondary glaucoma or even blindness. It is most often seen in the iris but may be found on the eyelid, corneoscleral limbus, conjunctiva, orbit, retina, choroid, disc, or optic nerve. Of patients with ocular JXG, 92% are younger than the age of two. Although cutaneous JXG usually disappear spontaneously, ocular lesions rarely improve spontaneously and require treatment.