Table 1.
Clinical and investigational findings in 10 patients with N2O-induced subacute degeneration of the spinal cord
| Case | Number of reported N2O canisters per week | UL sensory | LL sensory | UL distal motor power | LL distal motor power | UL reflexes | LL reflexes | Gait ataxia | Bladder/bowel | Other | Vitamin B12 level (ng/L) | MMA level (μmol/L) | MRI at presentation | Follow-up MRI* |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 100 | PP/JPS/LT loss | Vib loss | IV | IV | + | +++ C | Y | Nil | Myoclonic jerks, Uhtoff’s | 138 | 0.7 | C2–7 dorsal column hyperintensity and enhancement | Persistent dorsal column hyperintensity, enhancement resolved |
| 2 | 1000 | JPS/Vib loss | Vib loss | V | V | ++ | ++ | Y | Nil | Lhermitte’s, PA | 169 | ND | C1–7 dorsal column hyperintensity, cord atrophy | ND |
| 3 | 300 | HA/PP loss | HA PP, Vib loss | V | V | + | +++ C | Y | Constipation | PA | 196 | 2.36 | C1–6 dorsal column hyperintensity | ND |
| 4 | 192 | JPS/Vib loss | JPS/Vib loss | IV | IV | (+) | (+) | N | Nil | PA | > 2000*** | ND | C1–7 dorsal column hyperintensity | ND |
| 5 | 500 | Normal | PP/JPS loss | V | IV | 0 | 0 | Y | Nil | Nil | 186 | 3.45 | C2–6 dorsal column hyperintensity | ND |
| 6 | 600 | Normal | HA PP/JPS/Vib loss | IV | IV | ++ | +++ | Y | Nil | Nil | 109 | 110 | ND | ND |
| 7 | 75 | JPS loss | PP/JPS/Vib/LT loss | V | V | ++ | ++ | Y | Nil | PA | 321*** | 0.16 | C3–5 dorsal column hyperintensity | Complete resolution |
| 8** | 180 | Normal | LT loss | V | V | ++ | 0 | N | Nil | Nil | 229 | 14 | C2–6 dorsal column hyperintensity | Persistent dorsal column hyperintensity |
| 9 | 700 | Normal | HA PP/JPS/Vib loss | V | IV | ++ | 0 | Y | Nil | Nil | 169 | 0.61 | C1–7 dorsal column hyperintensity | ND |
| 10** | 1500-2000 | PP/JPS/Vib loss | PP/JPS/Vib loss | V | V | + | + | Y | Nil | PA | 226 | 7.8 | C4–7 dorsal column hyperintensity | Complete resolution |
Power assessments according to MRC power score. Reflexes 0 = absent, (+) with reinforcement, + = diminished, ++ = normal, +++ = brisk, C = with clonus, UL = upper limbs, LL = lower limbs. MMA = methylmalonic acid. B12 reference range 191-900 ng/L, MMA 0.0-0.29umol/L
HA hyperaesthesia, LT light touch sensation, PP pin prick sensation, JPS joint position sensation, Vib vibration sensation, PA pseudoathetosis. ND not done/not available
* Follow-up MRI was performed at 5 months for case 1, 8 months case 7, 16 months case 8 and 27 months case 10
** both patients re-presented following a previous diagnosis of subacute degeneration of the spinal cord
*** Already on B12 replacement