Sir,

Case report

A 67-year-old woman presented with left-sided blurred vision on a background of temporal headaches, arthralgia (shoulder and jaw), and malaise. She also described seeing grey patches, which lasted for minutes, and hearing whooshing sounds.

Best corrected vision was 6/9 right and 6/12 left. Temporal arteries were tender on palpation. Ishihara test was normal, but subjectively red objects appeared 50% brighter through the left eye. Ocular examination was otherwise unremarkable. Blood tests showed ESR 47 and CRP 6.3. Visual fields (Figure 1) and MRI brain (Figure 2) revealed nonspecific abnormalities.

Figure 1
figure 1

Visual field maps (24-2) showed nonspecific superior defects.

Full size image
Figure 2
figure 2

MRI brain showed foci of hyperdensities in the deep white matter and hypodensities in the lentiform nuclei (arrows).

Full size image

Patient was admitted for suspected giant cell arteritis (GCA). Doppler ultrasound of temporal arteries and left temporal artery biopsy (TAB) were negative. After 4 days of steroid treatment, the headache and arthralgia improved but vision remained unchanged. Repeat bloods were normal. Patient was discharged on oral prednisolone.

Upon arriving home, she was intrigued to discover her kitchen covered in soot. Concerns from her daughter led to investigation by a gas technician who confirmed CO production from the boiler. Carboxyhaemoglobin level the following day measured 1.9% (normal <1.5% in non-smoker). She recalled retrospectively that her various symptoms started after installing double glazing 1 year ago. Steroid was weaned off. At 2 months follow-up she was symptom-free and vision had recovered to 6/9 in both eyes.

Discussion

Chronic low level CO exposure is substantially under-recognised.1 Symptoms are vague and severity fluctuates as carboxyhaemoglobin has a half-life of 4 h once fresh air is reintroduced. Radiographic abnormalities in the lentiform nuclei and deep white matter are consistent with previous reports and likely results of hypoxia within watershed zones.2

Visual manifestations are slow in both onset and resolution.3 Transient scotomas (seen as grey patches), nonspecific field defects, reduced acuity, and kakopsia (colours appearing brighter) could all occur due to impairment of the primary visual cortex.4 Whooshing sounds were likely hallucination originating from auditory cortex. The vivid combination of visual and auditory disturbances has been found to explain alleged haunted houses.5

The lesson is that CO poisoning can mimic GCA and should form part of the differential. Focused social history and carboxyhaemoglobin level can help exclude the condition.