Dropped head syndrome (DHS) is characterized by severe paravertebral extensor muscle weakness, resulting in chin-on-chest deformity [¹]. Various conditions associated with DHS have been reported, including neuromuscular diseases, e.g. myasthenia gravis, motor neuron disease, congenital myopathy, chronic inflammatory demyelinating polyneuropathy, and mitochondriopathy [²]. Some of these conditions that present with DHS are progressive and systemic, and have a grave prognosis, such as amyotrophic lateral sclerosis [³]. Others have a benign clinical course without generalized neuromuscular disorder, and are diagnosed as isolated neck extensor myopathy (INEM).

The indications for surgical treatment of INEM are controversial, since these conditions have only rarely been described [⁴]. We report here a case of DHS due to INEM that was successfully treated surgically, with a review of the literature.

While some cases of DHS are progressive and systemic, with a grave prognosis, others present with INEM in the absence of generalized neuromuscular disorder and have a benign clinical course [⁵].

One possible cause of INEM in the present case is mitochondrial disease [⁶]. However, it has been reported that the paraspinal cervical muscles develop pathological abnormalities with increasing age and that both ragged-red fibers and accumulation of mitochondria are frequent findings in aging cervical muscles [⁷]. Myasthenia gravis (MG) must be considered as another possible cause of INEM. The clinical history of patients affected by MG is usually characterized by weakness and fatigability of muscles on repeated activity that improve after rest. They usually present not only difficulties of holding their heads upright, but also weakness of legs and ptosis, diplopia and slurring of speech. However, D'Amelio et al. recently described an unusual case of MG, presenting the isolated weakness of neck extensor muscles [⁸]. A Tensilon test or edrophonium test is essential for the diagnosis of MG, however, the present case was not examined with these tests since the clinical feature was not typical for MG.

Since the number of reported cases is small, it is still controversial whether surgical treatment is indicated for drooped head syndrome. One case of failure after surgical treatment with posterior correction and fusion without anterior reconstruction has been reported [⁹]. The authors mentioned the risk of implant pullout and failure to achieve adequate fixation of instrumentation in elderly patients due to osteoporosis. As reported here, we recommend anterior bone grafting combined with fusion with posterior instrumentation for DHS. For patients with anterior and posterior fibrous contractures, anterior release combined with posterior release is necessary. Two staged surgery was safe to observe not only neurological deterioration after correction but also activities of daily life in new position. Posterior instrumentation of pedicle screws and lateral mass screws was necessary to get final correction after posterior release of contracted facet joints.

We have reported here a rare case of DHS due to INEM. Anterior combined posterior reconstruction surgery yielded a successful outcome. Pathologic study revealed myogenic atrophy in the cervical extensor muscles, though the pathogenesis of this case remains unclear.

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

The authors declare that they have no competing interests.

ZM, MA, YI carried out the immunohistochemical studies. TY, KI participated in the surgery and the design of the study, and KI contributed in the statistical analysis. SK and KI conceived the study and drafted the manuscript. All authors read and approved the final manuscript.

This research was supported by KAKENHI-20591787(KI).