She could complete a 5 km morning walk without trouble, had no weakness in her legs and appeared perfectly fine during the day. Yet something strange kept happening at home. She almost lost balance while washing her face and felt unsteady when walking at night with the lights off. What looked like an ordinary fitness routine hid a surprising neurological clue. A senior neurologist has now explained why this pattern should never be ignored by patients or families.
Dr Sudhir Kumar, a neurologist from Hyderabad, recently shared the case on X and described it as a clinical puzzle that highlights how subtle symptoms can point to an underlying deficiency. According to him, the patient was a 40-year-old woman who walked normally in daylight and showed no weakness in her legs. On the surface, there seemed to be little reason for concern. She remained active, mobile and capable of doing regular exercise.
However, the picture changed in situations where visual cues were reduced.
She reportedly lost balance while washing her face and also became unsteady while walking at night when the lights were off. These episodes were not caused by tiredness or muscle weakness. Instead, they reflected a deeper issue involving the body’s balance system.— hyderabaddoctor (@hyderabaddoctor)
Why daylight made a difference? Dr Kumar explained that the woman’s normal walking during the day was possible because vision was compensating for another sensory problem. When people move, the brain relies on multiple systems to maintain balance. Vision helps us judge position and movement. The inner ear contributes information about motion and orientation. Nerves in the body send signals about where the limbs are in space. If one of these systems is impaired, another may temporarily compensate. In this case, once vision was reduced, such as when closing the eyes while washing the face or walking in darkness, the hidden instability became obvious.
The diagnosis: Sensory ataxia Dr Kumar identified the condition as sensory ataxia caused by involvement of the posterior columns. The posterior columns are pathways in the spinal cord that carry signals related to vibration sense, position sense and body awareness. When these pathways are affected, a person may struggle to know exactly where their feet or legs are without looking. That is why someone can appear stable with eyes open but become unsteady when visual input is removed. He described this pattern as the clinical equivalent of a classic positive Romberg sign, a bedside neurological clue in which balance worsens significantly when a person stands with eyes closed.The most common cause: vitamin B12 deficiency According to Dr Kumar, the most common cause behind this presentation is Vitamin B12 deficiency. Vitamin B12 plays an essential role in nerve health and red blood cell production. When levels fall too low, the nervous system can be affected. Some people experience numbness, tingling, fatigue, memory changes or gait problems. In certain cases, balance issues may become one of the earliest noticeable symptoms.
Because the person may still seem strong and active, the underlying deficiency can be missed unless the pattern is recognised.
Dr Kumar’s key takeaway Dr Sudhir Kumar’s central message was straightforward: when someone walks fine in light but becomes unstable in the dark, doctors should consider a posterior column problem and evaluate for vitamin B12 deficiency.
A symptom that appears minor or unusual at home may sometimes be the clearest clue to what the body has been lacking all along.
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