This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Orthopaedics
The earliest manifestation of Alkaptonuria is - 
Select and explain. 
A. Ankylosis of lumbodorsal spine, B. Ochronotic arthritis, C. Prostatic calculi, D. Pigmentation of tympanic membrane
B: Ochronotic arthritis
Answer: B: Ochronotic arthritis 
Explanation: Ochronosis (Alkaptonuria)

Alkaptonuria is a rare, heritable disorder characterized by the appearance of homogentisic acid in the urine, dark pigmentation of the connective tissues (ochronosis) and calcification of hyaline and fibrocartilage.
The inborn error is an absence of homogentisic acid oxidase in the liver and kidney. Those affected usually remain asymptomatic until the 3rd & 4th decade when they present with pain and stiffness of the spine & (later) larger joints.
Dark pigmentation of ear cartilage & sclera and staining of clothes by homogentisic acid in sweat. Urine turns dark brown when it is alkalinized or if it is left to stand for some hours.
X-ray reveal narrowing & calcification of intervertebral discs. Peripheral joints show chondrocalcinosis & severe osteoarthritis.