**Question:** Which of the following is not a feature of Acute Bilirubin Encephalopathy?

A. Increased muscle tone and stiffness (hypertonia)
B. Hyperreflexia and clonus
C. Sleep disturbances and hallucinations
D. Jaundice

**Core Concept:** Acute Bilirubin Encephalopathy (ABE) is a neurological disorder caused by high levels of bilirubin in the blood, which crosses the blood-brain barrier and accumulates in the brain. Bilirubin, a product of heme degradation, is typically transported to the liver for excretion. When this process fails, bilirubin levels rise, leading to ABE.

**Why the Correct Answer is Right:** D. Jaundice is a hallmark feature of ABE, with yellow discoloration of the skin and sclera due to elevated bilirubin levels. The condition is characterized by bilirubin crossing the blood-brain barrier and causing neurological dysfunction.

**Why Each Wrong Option is Incorrect:**

A. Increased muscle tone and stiffness (hypertonia) is a feature of ABE, as bilirubin toxicity affects the central nervous system (CNS) and can lead to spasticity.

B. Hyperreflexia and clonus are signs of a heightened reflex response, which can be present in ABE due to bilirubin's effect on the CNS.

C. Sleep disturbances and hallucinations are common in ABE, as bilirubin accumulation affects the CNS and can lead to altered mental status.

**Clinical Pearl:**

Acute Bilirubin Encephalopathy is typically seen in newborns, particularly those with hyperbilirubinemia due to impaired bilirubin clearance or increased production, such as in jaundiced newborns. Early recognition and treatment are essential to prevent complications and improve outcomes in these patients.