Types of Apraxia
Apraxia is classified into four major forms affecting the upper limbs: ideomotor apraxia, limb-kinetic apraxia, conceptual apraxia, and ideational apraxia 1.
Primary Classification System
The classification of limb apraxia is based on a two-system model for the organization of action:
Conceptual System Disorders
- Conceptual (Ideational) Apraxia: Results from dysfunction of the conceptual system, reflecting an inability to select and use objects due to disrupted integration between systems subserving functional knowledge of actions and object knowledge 2
- Manifests as apraxia with tool use, such as difficulty cutting with a knife or utilizing a pencil 3
Production System Disorders
Ideomotor Apraxia: Results from impairment of the production system 2
Represents apraxia without tool use, including:
- Impaired imitation of hand and finger positions
- Difficulty performing gestures on demand
- Defective pantomime of object use 3
More common after left hemispheric stroke than right hemispheric stroke 4
Limb-Kinetic Apraxia: Also stems from production system dysfunction 2
Characterized by loss of dexterity and deftness in skilled movements 5
This is the only apraxia subtype that fulfills all exclusion, specificity, and consistency criteria 6
Clinical Context
Limb apraxia is defined as "a decrease or difficulty in performing purposeful, skilled movements" that cannot be attributed to hemiplegia or lack of effort 4. The disorder is located in the left fronto-parietotemporal hemisphere, adjacent to speech areas, which explains why patients with apraxia frequently also suffer from aphasia 3.
Important Diagnostic Considerations
The diagnosis relies primarily on exclusion criteria, ruling out:
- Elementary motor or sensory deficits
- Aphasia as the primary cause
- Lack of effort 6
A critical diagnostic challenge exists: patients may or may not show apraxia depending on the chosen assessment method or theoretical framework, making the definition somewhat arbitrary 6. This variability stems from the evolution from task-based approaches (gold standard tests) toward process-based approaches that deconstruct action systems into multiple cognitive processes.
Additional Forms Beyond Limb Apraxia
While the evidence focuses primarily on limb apraxia, other forms mentioned in the literature include:
Note: Terms like "gait apraxia" and "apraxia of eyelid opening" may be misnomers, demonstrating the lack of coherent nomenclature in this field 5.