A Caucasian male who suffers from a severe neurological disease dies of an overwhelming respiratory infection. Autopsy shows an atrophic precentral gyrus and thin anterior roots of the spinal cord. Light microscopy reveals a severe loss of neurons in the anterior horn of the spinal cord and in the hypoglossal and ambiguous cranial nerve nuclei; corticospinal tracts stain only faintly, indicating demyelinization.

Educational objective: Amyotrophic lateral sclerosis (ALS) causes both upper and lower motor neuron lesions. Loss of neurons of the anterior horns of the spinal cord (LMN lesion) causes muscle weakness and atrophy. Demyelination of the lateral corticospinal tract (UMN lesion) leads to spasticity and hyperretlexia.

A 16-year-old girl is brought to the emergency department after she became unresponsive. Temperature is 39.7 C (103.5 F), blood pressure is 70/40 mm Hg, and pulse is 130/min and thready. There is a diffuse petechial and ecchymotic skin rash. Laboratory testing reveals leukocytosis with left shift and evidence of disseminated intravascular coagulation and multiorgan failure. Despite aggressive interventions, the patient dies several hours after admission. Autopsy reveals hemorrhagic necrosis of many internal organs, including the bilateral adrenal glands.

Educational objective: Neisseria meningitidis can cause sepsis and circulatory collapse in previously healthy young individuals. Lipooligosaccharide, a virulence factor in the pathogens outer membrane, is the major underlying cause of disease severity.

An 8-month-old girl is brought to the office for evaluation of irritability and regression of motor skills. Her birth was unremarkable and she appeared to develop normally, but she can no longer sit or roll over. Her parents have also noticed that she startles easily with loud noises. Head circumference measurement is consistent with macrocephaly. Bilateral funduscopic evaluation shows a bright red fovea centralis that is surrounded by a contrasting white macula. Peripheral vision is decreased. Abdominal examination is normal.

Educational objective: Tay-Sachs disease is an autosomal recessive disorder caused by [3-hexosaminidase A deficiency, which results in GM2 ganglioside accumulation. Key clinical features include progressive neurodegeneration and a cherry-red macular spot. In contrast to patients with Niemann-Pick disease, those with Tay Sachs disease have no hepatosplenomegaly.