RESUMEN
Myasthenia gravis (MG) belongs to a spectrum of autoimmune diseases in which anti-acetylcholine receptor antibodies damage neuromuscular junctions. It is a relatively rare disease with a higher incidence among the female population. The classical presentation is fatigable fluctuating diplopia or ptosis and, uncommonly, dysphagia or dysphonia. Even though it is rare, this condition can affect any skeletal muscle groups, including the neck or proximal limb muscles. There have been no reported cases of MG presenting as isolated neck weakness. An 81-year-old female patient presented with neck weakness associated with mild discomfort that progressively worsened throughout the day. Examination revealed reduced cervical muscular motor strength only. All imaging and laboratory investigations were within normal limits, except anti-acetylcholine receptor antibodies (binding Ab 12.04 nmol/L, blocking Ab 52% while modulating Ab 84%) with moderately elevated creatine phosphokinase (CPK) levels (350 U/l). The patient was prescribed Mestinon 60 mg QID (pyridostigmine), which led to rapid and significant relief of neck weakness. The patient has been stable on the medication for two years. MG typically presents in middle-aged female populations but, rarely, can also present with atypical symptoms among the elderly. Clinicians should have a high index of suspicion for myasthenia presenting with fatigable muscle weakness to reduce investigative costs and morbidity.