This month’s case presented a 59-year-old woman presented with pain and fatigability of neck extension evolved over three months. The question was:
Dropped head syndrome is a recognized manifestation of all of the following except:
1. MuSK myasthenia gravis
2. Amyotrophic lateral sclerosis
3. Facioscapulohumeral muscular dystrophy
5. Myotonia congenita
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The Correct Answer is 5: Myotonia congenital. The ability to hold the head up is made possible by at least five pairs of neck extensor muscles (NEM). It is a function that is taken for granted until it becomes defective. An average human head weighs eight pounds. Animals have more developed neck extensors. Weakness of the extensors initially leads to inability to lift the head off the pillow; therefore the patient has to turn to the side before sitting up. With progression, it becomes hard to hold the head up for a long time, and then the head drops all the time so that the patient has to hold his or her chin up to see. Excessive strain on the neck extensors leads to posterior cervical pain, which is a common early manifestation. MRIs reveal that the affected muscles appear atrophic, edematous, and replaced by fat. Common causes of dropped head syndrome include: 1. ALS: Weakness of the NEMs is usually accompanied by bulbar dysfunction (dysphagia, dysarthria, dyspnea) and features of upper and lower motor neuron lesions. It is progressive and diagnosis is hardly difficult. Mild CK elevation may sway the diagnosis toward a myopathic process but widespread denervation by EMG is usually evident. 2. Myasthenia Gravis: Usually fatigable diplopia and ptosis are present. In MuSK myasthenia gravis, dysphagia, fluctuating dyasarthia, and tongue weakness, and atrophy may lead to diagnostic confusion with ALS, which shows decremental response in about 30 percent of cases. Even tongue fasciculations are reported in cases with MuSK MG. It is strongly recommended that MuSk AB is tested in patients with dropped head syndrome. 3. Inflammatory myopathies 4. Metabolic myopathies such as acid maltase deficiency 5. Adult onset remain myopathy with monoclonal gammopathy 6. Facioscapulohumeral muscular dystrophy (FSHD) and dysferlinopathies 7. Dystrophic myopathies 8. Chronic inflammatory demyelinating polyneuropathy After extensive evaluation, at least 25 percent of neck extensor weakness remains idiopathic (INEM). There are reports of response to immunomodulation. Some cases may represent restricted seronegative myasthenia while others may represent restricted muscular dystrophy. The finding of spontaneous activity in cervical paraspinal muscles should not be over-interpreted. These changes can be secondary to the drop and not primary.