What is anterocollis?

What is Anterocollis?

Anterocollis is a form of cervical dystonia characterized by involuntary forward flexion of the neck due to abnormal, sustained contractions of the cervical flexor muscles. 1, 2

Clinical Characteristics

Anterocollis presents as abnormal forward bending of the neck that results from patterned, repetitive muscle contractions affecting the cervical flexor muscles. 2 The condition produces visible forward head posture that can be debilitating and painful. 1, 3

Key Clinical Features:

• Forward neck flexion is the defining postural abnormality 2
• Pain is commonly associated with the abnormal posture 3
• Complex dystonic patterns often exist, with anterocollis frequently occurring as part of a more widespread dystonic picture, including Meige syndrome in many cases 1
• Three distinct postural subtypes can be identified: posterior sagittal shift, head flexion, or neck flexion, or combinations thereof 1

Associated Conditions and Demographics

Anterocollis occurs in approximately 6.8% of cervical dystonia patients and shows a female predominance (67.3%). 2

Common Associations:

• Parkinsonian syndromes, particularly Parkinson's disease 2, 4
• Multiple system atrophy (though less commonly than previously thought) 2
• Neuroleptic exposure 2
• Family history of movement or neurological disorders 2

Pathophysiology

Two distinct subtypes exist based on underlying mechanism: 4

1. Myopathic subtype: Characterized by weakness of cervical extensor muscles with myopathic changes on EMG, more commonly associated with dopamine agonist use 4

2. Dystonic subtype: Characterized by overactivity of cervical flexor muscles without significant extensor weakness 4

Both subtypes may show myopathic changes on electromyography, though these are more prominent in patients with extensor weakness. 4

Muscles Involved

The primary muscles responsible for anterocollis include: 1, 3

• Deep cervical flexors (DCF), particularly the longus colli and longus capiti 1, 3
• Sternocleidomastoid (SCM) muscles 1, 3
• Supra-hyoid (SH) muscles 1
• Anterior scalene muscles 3

The longus colli plays a particularly important role in neck flexion but is often overlooked in treatment planning. 3

Treatment Approach

Botulinum toxin injection is the primary treatment for anterocollis, though this condition represents a disproportionate number of treatment failures when only superficial muscles are targeted. 3

Effective Treatment Strategy:

• Target multiple muscle groups including deep cervical flexors (longus colli/capiti), SCM, and supra-hyoid muscles in the same treatment session 1
• Use image guidance (fluoroscopy, EMG, or ultrasound) to accurately inject deep cervical muscles like the longus colli 3, 5
• Select specific deep flexor muscles based on the anterocollis posture subtype (longus capiti vs. longus colli) 1
• Tetrabenazine may provide clinical improvement in some cases 2

Treatment Outcomes:

When all dystonic muscles are properly targeted, approximately 50% of patients achieve dramatic improvement with 90% or greater satisfaction. 1 However, incomplete muscle selection is a major cause of treatment failures. 3

Important Clinical Pitfalls

• Injecting only superficial muscles (SCM and anterior scalenes) frequently results in treatment failure because the deep cervical flexors are not addressed 3
• Mild dysphagia can occur after botulinum toxin injection, particularly with dose increases, but serious complications are rare 3
• Anterocollis is heterogeneous with at least two distinct subtypes requiring different therapeutic considerations 4