Which of the following conditions is characterized by neck muscle contraction that twists the head to one side?

Spasmodic torticollis, also known as cervical dystonia, is a neurological movement disorder characterized by involuntary contractions of the neck muscles. These contractions lead to abnormal head postures, typically resulting in the head twisting toward one side. This condition can cause significant discomfort and may impact a person's ability to perform daily activities.

The defining feature of spasmodic torticollis is the specific action of the neck muscles that causes the head to turn or tilt, which clearly distinguishes it from other conditions. While cervical dystonia refers to a broader category of dystonic movements in the neck, the term spasmodic torticollis specifically highlights the same involuntary muscle contractions causing the head position abnormalities.

Other conditions listed, such as myoclonus, pseudoparkinsonism, and cervical dystonia, do not specifically describe the twisting nature of neck contractions or are related to different underlying mechanisms. Thus, identifying spasmodic torticollis is crucial for appropriate diagnosis and management of the condition.