Adult methylmalonic acidemia presented as neuromyelitis optica: one case report

Abstract

A 26-year-old male was admitted to our department, complaining of cognitive impairment, urine incontinence for 3 months, blurred vision for one month and numbness of bilateral lower limbs for 20 days. Presumed as “depression” and “viral encephalitis”, antidepressant and dexamethasone had been given but had no response. Neurological examination demonstrated impaired orientation to time and place; hearing impairment of right ear; normal muscle force in upper limbs, proximal lower muscle force was 2 and distal was 0; normal tendon reflex in both upper limbs; diminished tendon reflex in both lower limbs; left palmomental reflex (+); bilateral Babinski sign (+). Below T₁₀: diminished superficial, deep sensation and cortical sensory. Cranial MRI on admission revealed widened sulci in bilateral cleft and frontal, temporal and insular lobes, indicating brain atrophy. Spinal MRI revealed high-intensity signals of C_3-7 level and T_1-12 level. The patient was diagnosed as “neuromyelitis optica (NMO)” at first, but cognitive impairment is really rare in NMO. It finally turned out to be “inherited metabolic diseases” with the negative results of aquaporin 4 (AQP4), NMO-IgG, GM1, voltage-gated potassium channel (VGKC) from serum and cerebrospinal fluid (CSF). The elevated level of plasm homocysteine [30.79 mmol/L (5-20 mmol/L)] and urine methylmalonic acid [0.40 mmol/L (0.001 mmol/L)] ascertained the diagnosis of methylmalonic acidemia. The patient was given oral treatment of folate 5 mg (3 times a day, 13 days) and levocarnitine 1 g (3 times a day, 8 days) and intramuscular injection of mecobalamine 1mg (once a day, 4 days) or 0.50 mg (once a day, 8 days) and adenosylcobalamine 0.50 mg (once a day, 8 days). Sixteen days on discharge, the patient’s neurological examination revealed no obvious recovery of vision; lower muscle force: about Ⅳ, right sensory level: T₁₂-L₁, and left sensory level lowered to L₃. Reexamination of MRI revealed brain atrophy; the range of intramedullary high-intensity signals on C_3-7 level was enlarged; high-intensity signals on T_1-12 level. The level of plasm homocysteine was 74.40 mmol/L. One month later, during the follow-up, the patient could walk independently and had no sphincter disturbance.

DOI: 10.3969/j.issn.1672-6731.2015.10.014