Case Presentation: A 49-year-old man with type 2 diabetes was admitted to our hospital because of impaired consciousness. The patient was fatigued for 10 days and had visited his primary care physician who administered an intravenous drip the day before admission. In ER, he was unconscious with a Glasgow Coma Scale of 6; his breathing pattern was classified as Kussmaul breathing. Neurological deficits were not observed. Red papules and reticulate pigmentation were observed on the chest, abdomen, and back of the patient; this condition did not appear the previous day while the patient was at home. Laboratory data revealed dehydration, electrolytic imbalance, hyperglycemia (862 mg/dl), acidosis (pH 6.80), and urinary ketones. The patient was diagnosed with ketoacidosis due to cessation of diabetes therapy. Other triggers of ketoacidosis, such as infection, heavy drinking, or overeating, were ruled out. Prurigo pigmentosa was diagnosed by a dermatologist based on the presence of red papules and reticulate pigmentation. The patient underwent insulin treatment and was given liquids for rehydration. Blood glucose levels reduced to approximately 200 mg/dl by day 2 of admission and consciousness was regained. The red papules and reticulate pigmentation mostly resolved without administration of specific medication, such as minocyclin, although some pigmentation changes remained. The patient was discharged after his blood glucose level stabilized on day 17.

Discussion: Prurigo pigmentosa is a rare inflammatory dermatosis of unknown etiology and is characterized by a rash that consists of itchy, reddish papules coalescing to form a reticulated pattern. It commonly presents on the back, chest, and neck. Disease progression is divided into three stages: early, fully developed, and late. Each stage is distinguished by unique clinical and histologic features. The mechanism of pathogenesis of prurigo pigmentosa may be related to neutrophil-mediated inflammation. Alternatively, mechanical stimulation, contact allergy, or climate may contribute to its development. Some studies have indicated underlying diseases, such as adult-onset Still’s disease, atopy, Helicobacter pylori infection, and Sjögren’s syndrome, in patients with prurigo pigmentosa. Patients with conditions that can potentially lead to ketosis, such as anorexia nervosa and diabetes, may also be at a higher risk of developing prurigo pigmentosa. Although treatment of hyperketonemia with glycemic control can be used to resolve prurigo pigmentosa, dapsone or minocyclin also may be effective treatments; both agents inhibit migration and/or function of neutrophils.

Conclusions: Physicians should consider prurigo pigmentosa when unconscious patients with diabetes present with characteristic exanthema patterns. If such a case arises, ketoacidosis should be managed appropriately.