MRCP2-3115
A 58-year-old man presented to his GP with complaints of weight loss and weakness that he had been experiencing for some time. He mentioned that his clothes no longer fit him properly. He had noticed progressive weakness in both his legs, along with wasting of the thighs and thinning around the ankles. Additionally, he had been experiencing slurring of speech and nasal regurgitation while eating. His medical history included chronic bronchitis, prostatic hypertrophy, and osteoarthritis affecting the cervical and lumbar spine. He was currently taking a salbutamol and beclasone inhaler.
Upon examination, the patient appears cachectic with muscle wasting in his arms and legs. Chest and abdominal examination appeared normal. Cranial nerve examination revealed a pseudobulbar palsy, decreased palatal elevation, and wasting of the tongue with fasciculations. There was also a brisk jaw jerk. Upper limb examination showed normal tone, but asymmetrical wasting of the forearms and dorsal interossei bilaterally. There was also asymmetrical weakness of hand grip (right greater than left) and weakness of wrist flexion/extension. Reflexes appeared pathologically brisk, and there were positive Hoffman signs bilaterally. Lower limb examination revealed bilaterally increased tone with fasciculations of the thighs. There was marked weakness of dorsiflexion and plantar flexion of the left foot and bilateral weakness of hip flexion that was more pronounced on the left than the right. Sensory examination and cerebellar function were normal.
Blood tests showed normal liver function, sodium, potassium, urea, creatinine, and prostate specific antigen levels. The patient’s calcium level was slightly elevated. MR brain and chest x-ray were normal, but MRI spine showed degenerative disc disease affecting the lumbar and cervical spine. Electromyography and nerve conduction studies revealed spontaneous fasciculation potentials affecting all four limbs.
What is the most likely cause of this patient’s symptoms based on his history and clinical findings?