Video Case Solution: Diagnosis: Myasthenic Neck Extensor Weakness

Read the case description and watch the video online at PracticalNeurology.com.

The most likely cause of this dropped head syndrome is:
1. Amyotrophic lateral sclerosis
2. Myasthenia gravis
3. Lambert Eaton Syndrome
4. Polymyositis
5. Guillain Barre syndrome

DIAGNOSIS: MYASTHENIC NECK EXTENSOR WEAKNESS

This patient was placed on plasmapheresis and oral prednisone and his symptoms resolved within two months.

• Weak neck extensor muscles can be the initial manifestation of MG, but in that case it usually develops with other ocular and bulbar symptoms such as diplopia, ptosis, dysarthria, dysphagia, dyspnea, and fatigability of the chewing muscles.

• It is imperative to test fatigability of neck extensors in all myasthenics even if they do not complain of weakness of these muscles. Increased fatigability of the neck extensors and triceps muscle is often used to differentiate MG from myopathies where weakness usually affects neck flexors and deltoid.

• One has to be careful when performing repetitive neck flexion/extension testing in elderly with severe cervical spondylosis and patients with history of neck trauma.

• Dropped head due to MG is usually not as pronounced in the mornings.

• MuSK antibodies associated MG are more likely to present with dropped head as the main feature.

  • The lack of ocular involvement and the atrophy of the tongue and pharynx may lead to diagnostic confusion with ALS. Dysarthria is not a differentiating feature as it occurs in both. Measurement of MuSK Ab is important in all cases of dropped head syndrome.

• A therapeutic steroid trial may be warranted in uncertain cases.

• Weakness and fatigability of neck extensors usually start improving within three weeks of initiation of steroids.

• Dropped head due to MG usually respond well to treatment of MG.